Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2019	May 08, 2019
Document and Entity Information [Abstract]
Entity Registrant Name	Cyclerion Therapeutics, Inc.
Entity Central Index Key	0001755237
Document Type	10-Q
Document Period End Date	Mar. 31, 2019
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Trading Symbol	cycn
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Common Stock, Shares Outstanding		27,401,660
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1

Condensed Combined Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Current assets:
Prepaid expenses	$ 927	$ 867
Other current assets	12	12
Total current assets	939	879
Property and equipment, net	8,815	6,497
Other assets	19	25
Total assets	9,773	7,401
Current liabilities:
Accounts payable	5,671	2,781
Accrued research and development costs	6,243	5,261
Accrued expenses and other current liabilities	5,559	9,804
Total current liabilities	17,473	17,846
Other liabilities	52
Net parent investment:
Net parent investment	(7,752)	(10,445)
Total liabilities and net parent investment	$ 9,773	$ 7,401

Condensed Combined Statements of Operations - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cost and expenses:
Research and development	$ 26,404	$ 21,514
General and administrative	10,977	3,769
Total cost and expenses	37,381	25,283
Loss from operations	(37,381)	(25,283)
Net loss	$ (37,381)	$ (25,283)

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Condensed Combined Statements of Net Parent Investment - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Change in Net Parent Investment
Parent company net investment, beginning of period	$ (10,445)	$ (8,567)
Net loss	(37,381)	(25,283)
Net transfers from Parent	36,085	26,591
Parent allocation - Share-based compensation	3,989	2,508
Parent company net investment, end of period	$ (7,752)	$ (4,751)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Condensed Combined Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities:
Net loss	$ (37,381)	$ (25,283)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	525	356
Share-based compensation expense	3,989	2,508
Changes in assets and liabilities:
Prepaid expenses	(60)	(19)
Other current assets		8
Other assets	6	18
Accounts payable	2,890	1,362
Accrued research and development costs	982	(2,235)
Accrued expenses and other current liabilities	(5,274)	(3,144)
Other liabilities	52
Net cash used in operating activities	(34,271)	(26,429)
Cash flows from investing activities:
Purchases of property and equipment	(1,814)	(162)
Net cash used in investing activities	(1,814)	(162)
Cash flows from financing activities:
Transfer from Parent Company	36,085	26,591
Net cash provided by financing activities	36,085	26,591
Net increase (decrease) in cash and cash equivalents	0	0
Cash and cash equivalents, beginning of period	0	0
Cash and cash equivalents, end of period	0	0
Non-cash investing activities
Fixed asset purchases in accounts payable and accrued expenses	$ 1,029	$ 680

Nature of Business	3 Months Ended
Nature of Business	Mar. 31, 2019
Nature of Business
Nature of Business	1. Nature of Business Nature of Operations Cyclerion Therapeutics, Inc. (“Cyclerion” or the “Company”) is a clinical‑stage biopharmaceutical company harnessing the power of soluble guanylate cyclase (“sGC”) pharmacology to discover, develop and commercialize breakthrough treatments for serious and orphan diseases. Cyclerion’s focus is enabling the full therapeutic potential of next‑generation sGC stimulators. The Company’s strategy rests on a solid scientific foundation that is enabled by our people and capabilities, external collaborations, and a responsive capital allocation approach. The Separation In May 2018, Ironwood Pharmaceuticals, Inc. (“Ironwood” or the “Parent”) announced its plans to separate its sGC business from its commercial and gastrointestinal business. In furtherance of this plan, on March 6, 2019, Ironwood’s board of directors approved the distribution of all of the issued and outstanding shares of Cyclerion common stock on the basis of one share of Cyclerion common stock for every 10 shares of Ironwood common stock issued and outstanding on March 19, 2019, the record date for the distribution, which is referred to herein as the Distribution. On January 7, 2019, in connection with the Distribution, the Company and various investors entered into a common stock purchase agreement, which was subsequently amended and restated on February 25, 2019 (the “Amended and Restated Common Stock Purchase Agreement”), pursuant to which, upon the completion of the Distribution, these investors have made an aggregate cash investment in Cyclerion of $175 million in exchange for shares of Cyclerion common stock. On February 25, 2019, Cyclerion and various investors entered into an amended and restated common stock purchase agreement pursuant to which these investors have made an aggregate cash investment in Cyclerion of $175 million in exchange for shares of Cyclerion common stock. On April 1, 2019, Ironwood completed the previously announced separation of its sGC business, and certain other assets and liabilities, into a separate, independent publicly traded company by way of a pro-rata distribution of all of the outstanding shares of common stock of Cyclerion Therapeutics, Inc. through a dividend distribution of one share of the Company’s common stock, with no par value per share, for every 10 shares of Ironwood common stock held by Ironwood stockholders as of the close of business on March 19, 2019, the record date for the Distribution (the entire transaction being the “Separation”). As a result of the Separation, the Company became an independent public company and commenced regular way trading under the symbol “CYCN” on the Nasdaq Global Select Market on April 2, 2019. In connection with the Separation, on March 30, 2019, the Company entered into certain agreements with Ironwood to provide a framework for the Company’s relationship with Ironwood following the Separation, including, among others, the Separation Agreement, Tax Matters Agreement, and Employee Matters Agreement. In addition, in connection with the Separation, on April 1, 2019, the Company entered into a Development Agreement, an Ironwood Transition Services Agreement, a Cyclerion Transition Services Agreement and an Intellectual Property License Agreement with Ironwood. On April 2, 2019, the Company issued 11,817,165 shares (‘‘Private Placement Shares’’) of its common stock to accredited investors for gross proceeds of $175 million (net proceeds of approximately $165 million) pursuant to the Amended and Restated Common Stock Purchase Agreement. The funds associated with the sale of Private Placement Shares were received by the Company on April 2, 2019. Basis of Presentation The accompanying unaudited condensed combined financial statements have been prepared on a stand‑alone basis and are derived from Ironwood’s consolidated financial statements and accounting records. The unaudited condensed combined financial statements reflect the historical results of the operations, financial position and cash flows of Cyclerion, in conformity with United States generally accepted accounting principles (“U.S. GAAP”). These unaudited condensed combined financial statements of Cyclerion reflect the assets, liabilities, and expenses directly attributable to Cyclerion, as well as allocations of certain corporate level assets, liabilities and expenses, deemed necessary to fairly present the financial position, results of operations and cash flows of Cyclerion, as discussed further below. As such, these allocations may not be indicative of the actual amounts that would have been recorded had Cyclerion operated as an independent, publicly traded company for the periods presented. As part of Ironwood, Cyclerion was dependent upon Ironwood for all of its working capital and financing requirements, as Ironwood uses a centralized approach to cash management and financing its operations. There were no cash amounts specifically attributable to Cyclerion for the historical periods presented; therefore, there is no cash reflected in the combined financial statements. Accordingly, cash and cash equivalents, debt or related interest expense have not been allocated to Cyclerion in the combined financial statements. Financing transactions related to Cyclerion are accounted for as a component of Net Parent Investment in the combined balance sheets and as a financing activity on the accompanying combined statements of cash flows. Cyclerion’s condensed combined financial statements include an allocation of expenses related to certain Ironwood corporate functions, including senior management, legal, human resources, finance, information technology and quality assurance. These expenses have been allocated to Cyclerion based on direct usage or benefit where identifiable, with the remainder allocated pro‑rata based on project related costs, headcount or other measures. These allocations may not be indicative of the actual expense that would have been incurred had Cyclerion operated as an independent, publicly traded company for the periods presented. See Notes 8 and 10 for further description of the accounting for the Separation. The combined balance sheets of Cyclerion include assets and liabilities that were allocated principally on a specific identification basis. As Cyclerion was not historically held by a single legal entity, Net Parent Investment is shown in lieu of stockholder’s equity in the combined financial statements. Net Parent Investment represents the cumulative investment by Ironwood in Cyclerion through the dates presented, inclusive of operating results. Balances between Cyclerion and Ironwood that were not historically settled in cash are included in Net Parent Investment. All significant transactions between the Company and Ironwood have been included in the accompanying condensed combined financial statements. Transactions with Ironwood are reflected in the accompanying condensed combined statements of Net Parent Investment as Net Transfers from Parent, and in the accompanying condensed combined balance sheets within Net Parent Investment. Going Concern The Company has experienced negative operating cash flows for all historical periods presented. The Company expects these losses to continue into the foreseeable future as the Company continues the development and clinical testing of the product candidates, olinciguat, praliciguat and IW‑6463, and its discovery research programs. The Company completed a private placement financing that would fund operations through at least the next 12 months (see Note 10), but as of March 31, 2019, had not received the cash associated with the financing. Accordingly, the Company’s continued operations are dependent on its ability to raise additional capital through the sale of equity or debt securities. In the event that the Company is unable to raise sufficient funds, it would have to substantially alter, or possibly even discontinue or curtail operations, or sell assets at distressed prices. This uncertainty raises substantial doubt about the Company’s ability to continue as a going concern as of March 31, 2019. The accompanying financial statements do not include any adjustments that might result from the outcome of this uncertainty. On April 2, 2019, the Company issued 11,817,165 shares of its common stock to accredited investors for gross proceeds of $175 million (net proceeds of approximately $165 million) pursuant to the Amended and Restated Common Stock Purchase Agreement, dated February 25, 2019. The funds associated with the sale of Private Placement Shares were received by the Company on April 2, 2019, and as a result, the substantial doubt surrounding the Company’s ability to continue as a going concern has been alleviated. As of April 2, 2019, the Company, though it expects negative cash flows to continue through 2019 as it continues the development and clinical stage testing of its product candidates and its discovery research programs, expects to be able to fund operating expenses and capital expenditure requirements through the first quarter of 2021 (see Note 10).

Summary of Significant Accounting Policies

3 Months Ended

Mar. 31, 2019

Summary of Significant Accounting Policies

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Principles of Combination

The accompanying condensed combined financial statements include the accounts of Cyclerion. All significant intercompany transactions with Ironwood are deemed to have been paid in the period the costs were incurred. Expenses related to corporate allocations from Ironwood to the Company are considered to be effectively settled for cash in the condensed combined financial statements at the time the transaction was recorded.

Segment Information

Operating segments are components of an enterprise for which separate financial information is available and is evaluated regularly by the Company’s chief operating decision‑maker in deciding how to allocate resources and in assessing performance. The Company currently operates in one reportable business segment—human therapeutics.

Use of Estimates

The preparation of condensed combined financial statements in accordance with U.S. GAAP requires the Company’s management to make estimates and judgments that may affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the condensed combined financial statements, and the amounts of expenses during the reported periods. On an on‑going basis, the Company’s management evaluates its estimates, judgments and methodologies. Significant estimates and assumptions in the condensed combined financial statements include those related to allocations of expenses, assets and liabilities from Ironwood’s historical financials to the Company; impairment of long‑lived assets; income taxes, including the valuation allowance for deferred tax assets; research and development expenses; contingencies and share‑based compensation. The Company bases its estimates on historical experience and on various other assumptions that are believed to be reasonable, the results of which form the basis for making judgments about the carrying values of assets and liabilities. Actual results may differ materially from these estimates under different assumptions or conditions. Changes in estimates are reflected in reported results in the period in which they become known.

Cash and Cash Equivalents

The Company considers all highly liquid investment instruments with a remaining maturity when purchased of three months or less to be cash equivalents. Investments qualifying as cash equivalents may consist of money market funds, U.S. government‑sponsored securities and repurchase agreements. The carrying amount of cash equivalents approximates fair value. There were no cash amounts specifically attributable to Cyclerion for the historical periods presented; therefore, there is no cash reflected in the condensed combined financial statements.

Property and Equipment

Property and equipment are recorded at cost, and are depreciated when placed into service using the straight‑line method based on their estimated useful lives as follows:


		Estimated
		Useful Life
Asset Description		(In Years)
Laboratory equipment		5
Computer and office equipment		3
Furniture and fixtures		7
Software		3

Included in property and equipment are certain costs of software obtained for internal use. Costs incurred during the preliminary project stage are expensed as incurred, while costs incurred during the application development stage are capitalized and amortized over the estimated useful life of the software. The Company also capitalizes costs related to specific upgrades and enhancements when it is probable the expenditures will result in additional functionality. Maintenance and training costs related to software obtained for internal use are expensed as incurred. Costs for capital assets not yet placed into service have been capitalized as construction in progress, and are depreciated in accordance with the above guidelines once placed into service. Maintenance and repair costs are expensed as incurred.

Impairment of Long‑Lived Assets

The Company regularly reviews the carrying amount of its long‑lived assets to determine whether indicators of impairment may exist, which warrant adjustments to carrying values or estimated useful lives. If indications of impairment exist, projected future undiscounted cash flows associated with the asset are compared to the carrying amount to determine whether the asset’s value is recoverable. If the carrying value of the asset exceeds such projected undiscounted cash flows, the asset will be written down to its estimated fair value. There were no significant impairments of long‑lived assets for the three months ended March 31, 2019.

Research and Development Costs

The Company expenses research and development costs to operations as incurred. The Company defers and capitalizes nonrefundable advance payments made by the Company for research and development activities until the related goods are received or the related services are performed.

Research and development expenses are comprised of costs incurred in performing research and development activities, which may include salary, benefits and other employee‑related expenses; share‑based compensation expense; laboratory supplies and other direct expenses; facilities expenses; overhead expenses; third‑party contractual costs relating to nonclinical studies and clinical trial activities and related contract manufacturing expenses, development of manufacturing processes and regulatory registration of third‑party manufacturing facilities; licensing fees for the Company’s product candidates; and other outside expenses.

General and Administrative Expenses

The Company expenses general and administrative costs to operations as incurred. General and administrative expense consists of compensation, share‑based compensation, benefits and other employee‑related expenses for personnel in the Company’s administrative, finance, legal, information technology, business development and human resource functions. Other costs include the legal costs of pursuing patent protection of the Company’s intellectual property, general and administrative related facility costs, insurance costs and professional fees for accounting and legal services.

Patent Costs

The Company incurred and recorded as operating expense legal and other fees related to patents of approximately $0.4 million and $0.1 million for three months ended March 31, 2019 and 2018, respectively. These costs were charged to general and administrative expenses as incurred.

Subsequent Events

The Company considers events or transactions that have occurred after the balance sheet date of March 31, 2019, but prior to the filing of the financial statements with the Securities and Exchange Commission to provide additional evidence relative to certain estimates or to identify matters that require additional recognition or disclosure. Subsequent events have been evaluated through the filing of the financial statements accompanying this Quarterly Report on Form 10‑Q (see Note 10).

New Accounting Pronouncements

From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (“FASB”) or other standard setting bodies that are adopted by the Company as of the specified effective date. Except as discussed elsewhere in the notes to the combined financial statements, the Company did not adopt any new accounting pronouncements during the three months ended March 31, 2019 and 2018, that had a material effect on its combined financial statements.

In February 2016, the FASB issued ASU No. 2016‑02, Leases (“ASU 2016‑02”), which supersedes the lease accounting requirements in ASC Topic 840, Leases, and most industry‑specific guidance with ASC Topic 842, Leases. ASU 2016‑02 requires the identification of arrangements that should be accounted for as leases by lessees. In general, for lease arrangements exceeding a 12‑month term, these arrangements must now be recognized as assets and liabilities on the balance sheet of the lessee. Under ASU 2016‑02, a right‑of‑use asset and lease obligation will be recorded for all leases, whether operating or financing, while the income statement will reflect lease expense for operating leases and amortization and interest expense for financing leases. The balance sheet amount recorded for existing leases at the date of adoption of ASU 2016‑02 must be calculated using the applicable incremental borrowing rate at the date of adoption. ASU 2016‑02 is effective for fiscal years beginning after December 15, 2018, and interim periods within fiscal years beginning after December 15, 2019. In July 2018, the FASB issued ASU No. 2018‑10, Leases (Topic 842) (“ASU 2018‑10”), Codification Improvements and ASU No. 2018‑11, Leases (Topic 842) (“ASU 2018‑11”), to provide additional guidance for the adoption of Topic 842. ASU 2018‑10 clarifies certain provisions, and corrects unintended applications of the guidance, such as the rate implicit in a lease, impairment of the net investment in a lease, lessee reassessment of lease classifications, lessor reassessment of lease term and purchase options, variable payments that depend on an index or rate and certain transition adjustments. The amendments in ASU 2018‑11 will allow for an additional transition method, whereby at the adoption date the entity recognizes a cumulative‑effect adjustment to the opening balance of retained earnings in the period of adoption, while the comparative period disclosures continue recognition under ASC Topic 840. Additionally, ASU 2018‑11 includes a practical expedient for separating contract components for lessors. In December 2018, the FASB issued ASU No. 2018‑20, Leases (Topic 842) (“ASU 2018‑20”), Narrow-Scope Improvements for Lessors, which provided clarification for lessors on how to apply the new leases standard when accounting for sales taxes, certain lessor costs, and certain requirements related to variable payments in contracts. In March 2019, the FASB issued ASU No. 2019‑01, Leases (Topic 842) (“ASU 2019‑01”), Codification Improvements, which aligned the new leases guidance with existing guidance for fair value of the underlying asset by lessors that are not manufacturers or dealers. It also clarified an exemption for lessors and lessees from a certain interim disclosure requirement associated with adopting the board’s new lease accounting standard. The Company’s analysis includes, but is not limited to, reviewing existing leases, reviewing other service agreements for embedded leases, establishing policies and procedures, assessing potential disclosures and evaluating the impact of adoption on the Company’s combined financial statements. The Company adopted ASU 2016‑02, ASU 2018‑10, ASU 2018‑11, ASU 2018‑20, and ASU 2019‑01 in the first quarter of 2019. The adoption of these standards did not have a material impact on the Company’s financial position and the related footnote disclosures as of and for the three months ended March 31, 2019 under the current basis of presentation. The Company expects the adoption of these standards to have a material impact on the Company’s financial position and related footnote disclosures in the second quarter of 2019, related to the commencement of its premises lease (see Note 10).

In October 2016, the FASB issued ASU No. 2016‑16, Accounting for Income Taxes: Intra‑Entity Asset Transfers of Assets Other than Inventory (“ASU 2016‑16”). ASU 2016‑16 eliminates the ability to defer the tax expense related to intra‑entity asset transfers other than inventory. Under the new standard, entities should recognize the income tax consequences on an intra‑entity transfer of an asset other than inventory when the transfer occurs. ASU 2016‑16 is effective for fiscal periods beginning after December 15, 2018. The Company adopted this standard during the three months ended March 31, 2019. Adoption of this standard did not have a material impact on the Company’s financial position or results of operations.

In June 2018, the FASB issued ASU No. 2018‑07, Improvements to Nonemployee Share‑based Payments (“ASU 2018‑07”). ASU 2018‑07 simplifies the accounting for share‑based payments to nonemployees by aligning with the accounting for share‑based payments to employees, with certain exceptions. Measurement of equity‑classified nonemployee awards issued in exchange for goods or services used or consumed in an entity’s own operations will be fixed at the grant date, which may lower the cost and reduce volatility in the income statement. Entities also may use the expected term to measure nonemployee options or elect to use the contractual term as the expected term, on an award‑by‑award basis. ASU 2018‑07 is effective for the fiscal periods beginning after December 15, 2018. The Company adopted this standard during the three months ended March 31, 2019. Adoption of this standard did not have a material impact on the Company’s financial position or results of operations.

In August 2018, the FASB issued ASU No. 2018‑15, Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement that is a Service Contract (“ASU 2018‑15”). ASU 2018‑15 requires a customer in a cloud computing arrangement that is a service contract to follow the internal‑use software guidance in ASC 350‑40, Intangibles—Goodwill and Other—Internal Use Software (ASC 350‑40), to determine which implementation costs to capitalize as assets or expense as incurred. The internal‑use software guidance in ASC 350‑40 requires that certain costs incurred during the application development stage be capitalized and other costs incurred during the preliminary project and post‑implementation stages be expensed as they are incurred. A customer’s accounting for the hosting component of the arrangement is not affected by this guidance. The amendments in ASU 2018‑15 are effective for fiscal years beginning after December 15, 2019, with early adoption permitted. The Company is currently evaluating the potential impact that the adoption of ASU 2018‑15 may have on the Company’s financial position and results of operations.

No other accounting standards known by the Company to be applicable to it that have been issued by the FASB or other standard‑setting bodies and that do not require adoption until a future date are expected to have a material impact on the Company’s combined financial statements upon adoption.

Property and Equipment

3 Months Ended

Mar. 31, 2019

Property and Equipment

Property and Equipment

3. Property and Equipment

Property and equipment, net consisted of the following (in thousands):


	March 31,		December 31,
	2019		2018
Laboratory equipment	$	18,477	$	17,753
Software		2,609		2,593
Construction in progress		2,785		741
Computer and office equipment		961		901
Gross property and equipment		24,832		21,988
Less: accumulated depreciation and amortization		(16,017)		(15,491)
Property and equipment, net	$	8,815	$	6,497

As of March 31, 2019 and December 31, 2018, all of the Company’s property and equipment was located in Cambridge, Massachusetts.

Depreciation and amortization expense of the Company’s property and equipment was approximately $0.5 million and $0.4 million for the three months ended March 31, 2019 and 2018, respectively.

Accrued Expenses and Other Current Liabilities

3 Months Ended

Mar. 31, 2019

Accrued Expenses and Other Current Liabilities

Accrued Expenses and Other Current Liabilities

4. Accrued Expenses and Other Current Liabilities

Accrued expenses consisted of the following (in thousands):


	March 31,		December 31,
	2019		2018
Accrued incentive compensation	$	1,250	$	4,889
Salaries		547		1,513
Accrued vacation		1,258		1,048
Professional fees		1,157		1,019
Workforce reduction charges		787		565
Other		560		770
	$	5,559	$	9,804

Commitments and Contingencies	3 Months Ended
Commitments and Contingencies	Mar. 31, 2019
Commitments and Contingencies
Commitments and Contingencies	5. Commitments and Contingencies Other Funding Commitments As of March 31, 2019, the Company has several on‑going studies in various clinical trial stages. The Company’s most significant clinical trial expenditures are related to contract research organizations. These contracts are generally cancellable, with notice, at the Company’s option and do not have any significant cancellation penalties. Guarantees As permitted under Delaware law, Ironwood indemnifies its officers and directors for certain events or occurrences while the officer or director is, or was, serving at Ironwood’s request in such capacity, including any such officers who served as an officer or director of Cyclerion prior to the Separation. The maximum potential amount of future payments Ironwood could be required to make is unlimited; however, Ironwood has directors’ and officers’ insurance coverage that is intended to limit its exposure and enable it to recover a portion of any future amounts paid. On September 6, 2018, Cyclerion was incorporated in Massachusetts, and is subject to Massachusetts law. The Company enters into certain agreements with other parties in the ordinary course of business that contain indemnification provisions. These typically include agreements with directors and officers, business partners, contractors, clinical sites and customers. Under these provisions, the Company generally indemnifies and holds harmless the indemnified party for losses suffered or incurred by the indemnified party as a result of the Company’s activities. These indemnification provisions generally survive termination of the underlying agreements. The maximum potential amount of future payments the Company could be required to make under these indemnification provisions is unlimited. However, to date the Company has not incurred material costs to defend lawsuits or settle claims related to these indemnification provisions. As a result, the estimated fair value of these obligations is minimal. Accordingly, the Company did not have any liabilities recorded for these obligations as of March 31, 2019 or December 31, 2018.

Share-based Compensation Plans

3 Months Ended

Mar. 31, 2019

Share-based Compensation Plans

Share-based Compensation Plans

6. Share‑based Compensation Plans

Ironwood maintains certain share‑based compensation programs for the benefit of its officers, directors and employees, including employees of Ironwood who became employees of Cyclerion in connection with the Separation. Specifically, during the three months ended March 31, 2019 and 2018, Ironwood had two share‑based compensation plans pursuant to which awards were made to employees of the Company: the Amended and Restated 2010 Employee, Director and Consultant Equity Incentive Plan (“2010 Equity Plan”) and the Amended and Restated 2010 Employee Stock Purchase Plan (“2010 Purchase Plan”). Ironwood also had one share‑based compensation plan under which there are outstanding awards available to employees of the Company, but from which no further awards will be made: the Amended and Restated 2005 Stock Incentive Plan (“2005 Equity Plan”). All awards granted under the programs consist of shares of Ironwood common stock. Accordingly, the amounts presented are not necessarily indicative of future share‑based compensation and do not necessarily reflect the amount that Cyclerion would have issued as an independent, publicly traded company for the periods presented.

Share‑based compensation expense was allocated to Cyclerion using a combined specific identification and pro‑rata method based on internal project related costs and headcount that management believes are consistent and reasonable. Share‑based compensation under Ironwood’s incentive stock programs allocated to Cyclerion is reflected in the Company’s condensed combined statements of operations as follows for the three months ended March 31, 2019 and 2018 (in thousands):


	Three Months Ended
	March 31,
	2019		2018
Research and development	$	1,796	$	1,665
General and administrative		2,193		843
	$	3,989	$	2,508

Included in share‑based compensation expense of approximately $4.0 million and $2.5 million, is approximately $0.9 million and $0.7 million of share‑based compensation expense for employees that are directly attributable to Cyclerion for the three months ended March 31, 2019 and 2018, respectively.

Defined Contribution Plan	3 Months Ended
Defined Contribution Plan	Mar. 31, 2019
Defined Contribution Plan
Defined Contribution Plan	7. Defined Contribution Plan Ironwood maintains a defined contribution 401(k) Savings Plan in the form of a qualified 401(k) plan for the benefit of substantially all of its employees, which includes Ironwood employees who became Cyclerion employees. Subject to certain IRS limits, eligible employees may elect to contribute from 1% to 100% of their compensation. Ironwood contributions to the plan are at the sole discretion of Ironwood’s board of directors. Currently, Ironwood provides a matching contribution of 75% of the employee’s contributions, up to $6,000 annually. Compensation expense related to the 401(k) match was allocated to Cyclerion using a pro‑rata method based on project related costs and headcount that management believes are consistent and reasonable. Included in compensation expense is approximately $0.3 million and $0.2 million of expenses for employees that are directly attributable to Cyclerion for the three months ended March 31, 2019 and 2018, respectively.

Related Party Transactions	3 Months Ended
Related Party Transactions	Mar. 31, 2019
Related Party Transactions
Related Party Transactions	8. Related Party Transactions Relationship with Ironwood Historically, prior to April 1, 2019, the Company was managed and operated in the normal course of business under Ironwood. Accordingly, certain shared costs were allocated to the Company and reflected as expenses in the Company’s stand‑alone combined financial statements. The expenses reflected in the combined financial statements may not be indicative of expenses that will be incurred by the Company in the future. (a)Corporate costs Ironwood incurred significant corporate costs for services provided to Cyclerion. These costs included expenses for information systems, accounting, other financial services (such as treasury, audit and purchasing), human resources, legal, and facilities. A portion of these costs benefited Cyclerion and have been allocated to Cyclerion using a pro‑rata method based on project related costs, headcount, or other measures that management believes are consistent and reasonable. This methodology is applied consistently between periods however the magnitude of the allocation will vary based on the relationship of Cyclerion costs compared to those of Ironwood’s other operations. The allocated corporate costs included in the combined statements of operations were approximately $6.8 million and $3.6 million for the three months ended March 31, 2019 and 2018, respectively, and were included in general and administrative expenses for both periods. (b)Cash Management and Financing Cyclerion participated in Ironwood’s centralized cash management and financing programs. Disbursements were made through centralized accounts payable systems which are operated by Ironwood. Cash receipts were transferred to centralized accounts, also maintained by Ironwood. As cash is disbursed and received by Ironwood, it was accounted for by Cyclerion through Net Parent Investment. All obligations were financed by Ironwood and financing decisions were determined by central Ironwood treasury operations until the Separation. Other Related Party Transactions Ironwood has and currently obtains health insurance services for its employees, including employees of Ironwood who became employees of Cyclerion, from an insurance provider whose President and Chief Executive Officer became a member of Ironwood’s Board of Directors in April 2016. Expenses related to insurance premiums were allocated to Cyclerion using a pro‑rata method based on internal project assignments and headcount, that management believes are consistent and reasonable. Insurance premiums allocated to Cyclerion amounted to approximately $0.5 million and approximately $0.6 million for the three months ended March 31, 2019 and 2018, respectively, and is reflected in the Company’s condensed combined statements of operations. Accordingly, the amounts presented are not necessarily indicative of future expense and do not necessarily reflect the results that Cyclerion would have experienced as an independent company for the periods presented. At March 31, 2019 and December 31, 2018, the Company had no outstanding payable balance due to this related party. Peter Hecht, Ironwood’s former Chief Executive Officer and the Chief Executive Officer and board member of Cyclerion, donated 2.5 million of his shares of Ironwood common stock to American Endowment Foundation for the creation of a donor advised fund that divested these shares to invest $34.0 million in Cyclerion as part of the financing transaction completed by Cyclerion on April 2, 2019. Mark Currie, Ironwood’s former Chief Scientific Officer and President of Cyclerion and board member of Ironwood, has invested $4.0 million in Cyclerion as part of this financing. Dr. Currie and certain other investors have funded a portion of their investment through sales of Ironwood common stock. Given the aforementioned director and officer affiliations with both Ironwood and Cyclerion, these investments are considered to be related party transactions.

Workforce Reduction

3 Months Ended

Mar. 31, 2019

Workforce Reduction

Workforce Reduction

9. Workforce Reduction

On June 27, 2018, Ironwood, as part of its plans to separate its sGC business from its commercial and gastrointestinal business determined the initial organizational designs for the continuing Ironwood business and Cyclerion, including employees’ roles and responsibilities. As part of this process Ironwood initiated, a reduction in its headquarter‑based workforce by approximately 40 employees and substantially completed the reduction in its workforce during the year ending December 31, 2018. During the three months ended March 31, 2019, Ironwood did not record any costs related to this reduction in workforce.

On February 7, 2019, following further analysis of Ironwood’s strategy and core business needs, and in an effort to further strengthen the operational efficiency of its organization, Ironwood commenced a reduction in its workforce by 35 employees, primarily based in the home office. Ironwood completed the reduction in its workforce during the first quarter of 2019. Employees expected to go to Cyclerion were excluded from the workforce reduction; however certain charges associated with the reduction were allocated to Cyclerion. During the three months ended March 31, 2019, Ironwood recorded approximately $3.3 million in total costs related to this reduction in workforce for one-time employee severance and benefit costs. Expenses related to workforce reduction were allocated to Cyclerion using a pro rata method based on internal project assignments and headcount, that management believes are consistent and reasonable. Workforce reduction charges allocated to Cyclerion amounted to approximately $0.5 million recorded in research and development expense and approximately $0.1 million recorded in general and administrative expense for the three months ended March 31, 2019.

The following table summarizes the accrued liabilities activity allocated to Cyclerion in connection with the reduction in workforce for the three months ended March 31, 2019 (in thousands):


	Amounts						Amounts
	Accrued at						Accrued at
	December 31, 2018		Charges		Amount Paid		March 31, 2019
June 2018 Reduction		565		—		268		297
February 2019 Reduction		—		580		90		490
Total	$	565	$	580	$	358	$	787

Subsequent Events	3 Months Ended
Subsequent Events	Mar. 31, 2019
Subsequent Events
Subsequent Events	10. Subsequent Events The Company has assessed subsequent events from the balance sheet date through May 13, 2019, the date at which the financial statements were available to be issued. In connection with the Separation, on March 30, 2019, the Company entered into certain agreements with Ironwood to provide a framework for the Company’s relationship with Ironwood following the Separation, including, among others, the Separation Agreement, the Tax Matters Agreement, and the Employee Matters Agreement. In addition, in connection with the Separation, on April 1, 2019, the Company entered into a Development Agreement, an Ironwood Transition Services Agreement, a Cyclerion Transition Services Agreement and an Intellectual Property License Agreement with Ironwood. On April 1, 2019, Ironwood completed the previously announced separation of its sGC business, and certain other assets and liabilities, into a separate, independent publicly traded company by way of a pro-rata distribution of all of the outstanding shares of common stock of Cyclerion Therapeutics, Inc. through a dividend distribution of one share of the Company’s common stock, with no par value per share, for every 10 shares of Ironwood common stock held by Ironwood stockholders as of the close of business on March 19, 2019, the record date for the Distribution. As a result of the Separation, the Company became an independent public company and commenced regular way trading under the symbol ‘‘CYCN’’ on the Nasdaq Global Select Market on April 2, 2019. On April 2, 2019, the Company issued 11,817,165 shares of its common stock to accredited investors for gross proceeds of $175 million (net proceeds of approximately $165 million) pursuant to the Amended and Restated Common Stock Purchase Agreement. The Company received the funds associated with the sale of Private Placement Shares on April 2, 2019, and as a result, the substantial doubt surrounding the Company’s ability to continue as a going concern (as discussed in Note 1) has been alleviated. As of April 2, 2019, the Company, though it expects negative cash flows to continue through 2019 as it continues the development and clinical stage testing of its product candidates and its discovery research programs, expects to be able to fund operating expenses and capital expenditure requirements through the first quarter of 2021. Peter Hecht, Ironwood’s former Chief Executive Officer and the Chief Executive Officer and board member of Cyclerion, donated 2.5 million of his shares of Ironwood common stock to American Endowment Foundation for the creation of a donor advised fund that divested these shares to invest $34.0 million in Cyclerion as part of this financing. Mark Currie, Ironwood’s former Chief Scientific Officer and President of Cyclerion and board member of Ironwood, has invested $4.0 million in Cyclerion as part of this financing. Dr. Currie and certain other investors have funded a portion of their investment through sales of Ironwood common stock. Given the aforementioned director and officer affiliations with both Ironwood and Cyclerion, these investments are considered to be related party transactions. On April 1, 2019, the Company entered into a direct lease (the ‘‘Lease’’) for its existing operating premises consisting of approximately 114,000 rentable square feet of office and lab space on the first and second floors. The Lease is for a term of 123 months with two five-year extension options and certain expansion rights. The Lease includes a letter of credit of $7.7 million posted with the landlord as a security deposit. Cyclerion has also entered into customary non-disturbance arrangements with the building landlord’s mortgagee and with the property ground lessor recognizing Cyclerion’s leasehold interest in this property. As part of the Separation, certain improvements are being completed in the Company’s leased premises. To accommodate the post-Separation completion of such improvements, on March 31, 2019, the Company entered into a short-term swing space sublease of approximately 24,000 rentable square feet in Ironwood’s remaining premises to allow a portion of the Company’s workforce to continue to operate while such improvements are completed. The sublease is for an initial one-month term with several one-month extension options. The Company is responsible for completing all work to separate the premises and to improve its directly leased premises. On April 29, 2019, Andreas Busch, Ph.D. joined the Company as Chief Innovation Officer. Dr. Busch leads the Company’s Innovation Center. On May 3, 2019, the Company’s 100% wholly owned Swiss entity, Cyclerion GmbH was incorporated. The subsidiary is located in Zug, Switzerland and will support the Company’s Innovation Center.

Summary of Significant Accounting Policies (Policies)

3 Months Ended

Mar. 31, 2019

Summary of Significant Accounting Policies

Basis of Presentation

The accompanying unaudited condensed combined financial statements have been prepared on a stand‑alone basis and are derived from Ironwood’s consolidated financial statements and accounting records. The unaudited condensed combined financial statements reflect the historical results of the operations, financial position and cash flows of Cyclerion, in conformity with United States generally accepted accounting principles (“U.S. GAAP”).

These unaudited condensed combined financial statements of Cyclerion reflect the assets, liabilities, and expenses directly attributable to Cyclerion, as well as allocations of certain corporate level assets, liabilities and expenses, deemed necessary to fairly present the financial position, results of operations and cash flows of Cyclerion, as discussed further below. As such, these allocations may not be indicative of the actual amounts that would have been recorded had Cyclerion operated as an independent, publicly traded company for the periods presented.

As part of Ironwood, Cyclerion was dependent upon Ironwood for all of its working capital and financing requirements, as Ironwood uses a centralized approach to cash management and financing its operations. There were no cash amounts specifically attributable to Cyclerion for the historical periods presented; therefore, there is no cash reflected in the combined financial statements. Accordingly, cash and cash equivalents, debt or related interest expense have not been allocated to Cyclerion in the combined financial statements. Financing transactions related to Cyclerion are accounted for as a component of Net Parent Investment in the combined balance sheets and as a financing activity on the accompanying combined statements of cash flows. Cyclerion’s condensed combined financial statements include an allocation of expenses related to certain Ironwood corporate functions, including senior management, legal, human resources, finance, information technology and quality assurance. These expenses have been allocated to Cyclerion based on direct usage or benefit where identifiable, with the remainder allocated pro‑rata based on project related costs, headcount or other measures. These allocations may not be indicative of the actual expense that would have been incurred had Cyclerion operated as an independent, publicly traded company for the periods presented. See Notes 8 and 10 for further description of the accounting for the Separation. The combined balance sheets of Cyclerion include assets and liabilities that were allocated principally on a specific identification basis. As Cyclerion was not historically held by a single legal entity, Net Parent Investment is shown in lieu of stockholder’s equity in the combined financial statements. Net Parent Investment represents the cumulative investment by Ironwood in Cyclerion through the dates presented, inclusive of operating results. Balances between Cyclerion and Ironwood that were not historically settled in cash are included in Net Parent Investment. All significant transactions between the Company and Ironwood have been included in the accompanying condensed combined financial statements. Transactions with Ironwood are reflected in the accompanying condensed combined statements of Net Parent Investment as Net Transfers from Parent, and in the accompanying condensed combined balance sheets within Net Parent Investment.

Principles of Combination

Segment Information

Use of Estimates

Cash and Cash Equivalents

Property and Equipment

Property and equipment are recorded at cost, and are depreciated when placed into service using the straight‑line method based on their estimated useful lives as follows:


		Estimated
		Useful Life
Asset Description		(In Years)
Laboratory equipment		5
Computer and office equipment		3
Furniture and fixtures		7
Software		3

Impairment of Long-Lived Assets

Impairment of Long‑Lived Assets

Research and Development Costs

General and Administrative Expenses

Patent Costs

Subsequent Events

New Accounting Pronouncements

Summary of Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 2019

Summary of Significant Accounting Policies

Schedule of estimated useful lives of property and equipment


		Estimated
		Useful Life
Asset Description		(In Years)
Laboratory equipment		5
Computer and office equipment		3
Furniture and fixtures		7
Software		3

Property and Equipment (Tables)

3 Months Ended

Mar. 31, 2019

Property and Equipment

Schedule of property and equipment, net

Property and equipment, net consisted of the following (in thousands):


	March 31,		December 31,
	2019		2018
Laboratory equipment	$	18,477	$	17,753
Software		2,609		2,593
Construction in progress		2,785		741
Computer and office equipment		961		901
Gross property and equipment		24,832		21,988
Less: accumulated depreciation and amortization		(16,017)		(15,491)
Property and equipment, net	$	8,815	$	6,497

Accrued Expenses and Other Current Liabilities (Tables)

3 Months Ended

Mar. 31, 2019

Accrued Expenses and Other Current Liabilities

Schedule of accrued expenses and other current liabilities

Accrued expenses consisted of the following (in thousands):


	March 31,		December 31,
	2019		2018
Accrued incentive compensation	$	1,250	$	4,889
Salaries		547		1,513
Accrued vacation		1,258		1,048
Professional fees		1,157		1,019
Workforce reduction charges		787		565
Other		560		770
	$	5,559	$	9,804

Share-based Compensation Plans (Tables)

3 Months Ended

Mar. 31, 2019

Share-based Compensation Plans

Schedule of allocation of share-based compensation expense

Share‑based compensation under Ironwood’s incentive stock programs allocated to Cyclerion is reflected in the Company’s condensed combined statements of operations as follows for the three months ended March 31, 2019 and 2018 (in thousands):


	Three Months Ended
	March 31,
	2019		2018
Research and development	$	1,796	$	1,665
General and administrative		2,193		843
	$	3,989	$	2,508

Workforce Reduction (Tables)

3 Months Ended

Mar. 31, 2019

Workforce Reduction

Schedule of accrued liabilities activity allocated in connection with reduction in workforce activities

The following table summarizes the accrued liabilities activity allocated to Cyclerion in connection with the reduction in workforce for the three months ended March 31, 2019 (in thousands):


	Amounts						Amounts
	Accrued at						Accrued at
	December 31, 2018		Charges		Amount Paid		March 31, 2019
June 2018 Reduction		565		—		268		297
February 2019 Reduction		—		580		90		490
Total	$	565	$	580	$	358	$	787

Nature of Business (Details) $ in Millions	Apr. 02, 2019 USD ($) shares	Apr. 01, 2019	Mar. 19, 2019
Private Placement \| Subsequent Event
Nature of Business
Shares issued to accredited investors \| shares	11,817,165
Gross proceeds from issuance of shares to accredited investors	$ 175
Net proceeds from issuance of shares to accredited investors	$ 165
Ironwood
Nature of Business
Distribution exchange ratio (shares of Cyclerion per share of Ironwood)			0.1
Ironwood \| Subsequent Event
Nature of Business
Common stock dividend issued (shares of Cyclerion per share of Ironwood)		0.1

Summary of Significant Accounting Policies - Segment Information and Cash and Cash Equivalents (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) segment	Dec. 31, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Summary of Significant Accounting Policies
Number of reportable business segment \| segment	1
Cash amount reflected in the condensed combined financial statements \| $	$ 0	$ 0	$ 0	$ 0

Summary of Significant Accounting Policies - Property and Equipment (Details)	3 Months Ended
	Mar. 31, 2019
Laboratory equipment
Property and Equipment
Estimated Useful Life (In Years)	5 years
Computer and office equipment
Property and Equipment
Estimated Useful Life (In Years)	3 years
Furniture and fixtures
Property and Equipment
Estimated Useful Life (In Years)	7 years
Software
Property and Equipment
Estimated Useful Life (In Years)	3 years

Property and Equipment (Details) - USD ($) $ in Thousands	3 Months Ended
Property and Equipment (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Property and Equipment
Gross property and equipment	$ 24,832		$ 21,988
Less: accumulated depreciation and amortization	(16,017)		(15,491)
Property and equipment, net	8,815		6,497
Depreciation, Depletion and Amortization, Nonproduction	525	$ 356
Laboratory equipment
Property and Equipment
Gross property and equipment	18,477		17,753
Software
Property and Equipment
Gross property and equipment	2,609		2,593
Construction in progress
Property and Equipment
Gross property and equipment	2,785		741
Computer and office equipment
Property and Equipment
Gross property and equipment	$ 961		$ 901

Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Accrued Expenses and Other Current Liabilities
Accrued incentive compensation	$ 1,250	$ 4,889
Salaries	547	1,513
Accrued vacation	1,258	1,048
Professional fees	1,157	1,019
Workforce reduction charges	787	565
Other	560	770
Total	$ 5,559	$ 9,804

Commitments and Contingencies (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Commitments and Contingencies
No liabilities recorded	$ 0	$ 0

Share-based Compensation Plans (Details) $ in Thousands	3 Months Ended
Share-based Compensation Plans (Details) $ in Thousands	Mar. 31, 2019 USD ($) plan	Mar. 31, 2018 USD ($) plan
Share-based Compensation Plans
Share-based compensation allocated to Cyclerion	$ 3,989	$ 2,508
Share-based compensation directly attributable to Cyclerion employees	900	700
Research and development
Share-based Compensation Plans
Share-based compensation allocated to Cyclerion	1,796	1,665
General and administrative
Share-based Compensation Plans
Share-based compensation allocated to Cyclerion	$ 2,193	$ 843
Ironwood
Share-based Compensation Plans
Number of share-based compensation plans pursuant to which awards were made to employees \| plan	2	2
Number of share-based compensation plans with outstanding awards but from which no further awards will be made \| plan	1	1

Defined Contribution Plan (Details) - USD ($)	3 Months Ended
Defined Contribution Plan (Details) - USD ($)	Mar. 31, 2019	Mar. 31, 2018
Defined Contribution Plan
Defined contribution plan expense directly attributable to Cyclerion employees	$ 300,000	$ 200,000
Ironwood
Defined Contribution Plan
401 (k) Savings Plan	us-gaap:QualifiedPlanMember
Matching contribution (as a percent of employee's contributions)	75.00%
Maximum amount of employer matching contribution	$ 6,000
Ironwood \| Minimum
Defined Contribution Plan
Percent of compensation eligible employees may elect to contribute	1.00%
Ironwood \| Maximum
Defined Contribution Plan
Percent of compensation eligible employees may elect to contribute	100.00%

Related Party Transactions - Relationship with Ironwood (Details) - Ironwood - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Corporate costs
Related Party Transactions
Related party expense	$ 6,800	$ 3,600
Health insurance services
Related Party Transactions
Related party expense	500	600
Outstanding balance payable to related party	$ 0	$ 0

Related Party Transactions - Private Placement (Details) - Subsequent Event - Private Placement shares in Millions, $ in Millions	Apr. 02, 2019 USD ($) shares
Peter Hecht
Related Party Transactions
Number of shares of Ironwood common stock donated to American Endowment Foundation \| shares	2.5
American Endowment Foundation
Related Party Transactions
Investment in common stock by related party	$ 34.0
Mark Currie
Related Party Transactions
Investment in common stock by related party	$ 4.0

Workforce Reduction (Details) $ in Thousands			3 Months Ended
Workforce Reduction (Details) $ in Thousands	Feb. 07, 2019 employee	Jun. 27, 2018 employee	Mar. 31, 2019 USD ($)
Summarizes the accrued liabilities activity allocated to Cyclerion in connection with the reduction in workforce
Amounts accrued, beginning of period			$ 565
Charges			580
Amount Paid			358
Amounts accrued, end of period			787
June 2018 Reduction
Summarizes the accrued liabilities activity allocated to Cyclerion in connection with the reduction in workforce
Amounts accrued, beginning of period			565
Amount Paid			268
Amounts accrued, end of period			297
February 2019 Reduction
Summarizes the accrued liabilities activity allocated to Cyclerion in connection with the reduction in workforce
Charges			580
Amount Paid			90
Amounts accrued, end of period			490
Research and development
Summarizes the accrued liabilities activity allocated to Cyclerion in connection with the reduction in workforce
Charges			500
General and administrative
Summarizes the accrued liabilities activity allocated to Cyclerion in connection with the reduction in workforce
Charges			100
Ironwood \| June 2018 Reduction
Workforce Reduction
Reduction in workforce, number of employees \| employee		40
Summarizes the accrued liabilities activity allocated to Cyclerion in connection with the reduction in workforce
Charges			0
Ironwood \| February 2019 Reduction
Workforce Reduction
Reduction in workforce, number of employees \| employee	35
Summarizes the accrued liabilities activity allocated to Cyclerion in connection with the reduction in workforce
Charges			$ 3,300

Subsequent Events - Private Placement (Details) - Subsequent Event $ in Millions	Apr. 02, 2019 USD ($) shares	Apr. 01, 2019
Private Placement
Nature of Business
Shares issued to accredited investors \| shares	11,817,165
Gross proceeds from issuance of shares to accredited investors	$ 175
Net proceeds from issuance of shares to accredited investors	$ 165
Ironwood
Nature of Business
Common stock dividend issued (shares of Cyclerion per share of Ironwood)		0.1

Subsequent Events - Related Party Transactions (Details) - Subsequent Event - Private Placement shares in Millions, $ in Millions	Apr. 02, 2019 USD ($) shares
Peter Hecht
Nature of Business
Number of shares of Ironwood common stock donated to American Endowment Foundation \| shares	2.5
American Endowment Foundation
Nature of Business
Investment in common stock by related party	$ 34.0
Mark Currie
Nature of Business
Investment in common stock by related party	$ 4.0

Subsequent Events - Lease Transaction (Details) $ in Millions	Apr. 01, 2019 USD ($) ft² item	Mar. 31, 2019 ft²
Swing space sublease
Nature of Business
Lease rentable square feet		24,000
Subsequent Event \| Office and lab space
Nature of Business
Lease rentable square feet	114,000
Lease contract term	123 months
Lessee, Operating Lease, Existence of Option to Extend [true false]	true
Lease, number of renewal terms \| item	2
Lease renewal term	5 years
Letter of credit posted as a security deposit for lease \| $	$ 7.7

Subsequent Events - Subsidiary Information (Details)	May 03, 2019
Subsequent Event \| Cyclerion GmbH
Subsequent Events
Interest in subsidiary (as a percent)	100.00%