Organization and Description of Business	3 Months Ended
Organization and Description of Business	Mar. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Description of Business	Organization and Description of Business Description of Business Millendo Therapeutics, Inc. (the “Company”), a Delaware corporation, together with its subsidiaries, is a clinical stage biopharmaceutical company primarily focused on developing novel treatments for endocrine diseases where current therapies do not exist or are insufficient. The Company seeks to leverage its understanding of recent biological discoveries in endocrinology to continue to advance and build its pipeline in order to improve the lives of patients. The Company is currently developing nevanimibe (ATR-101) as a potential treatment for patients with classic congenital adrenal hyperplasia, (“CAH”), a rare, monogenic adrenal disease that requires lifelong treatment with exogenous cortisol, often at high doses. The Company also has a neurokinin 3-receptor (NK3R) antagonist (MLE-301) in its research and development pipeline, which it plans to develop as a potential treatment of vasomotor symptoms (“VMS”), commonly known as hot flashes and night sweats, in menopausal women. The Company is actively pursuing additional pipeline assets in treatment areas where it has knowledge and experience in developing drug product candidates. The Company seeks to identify assets that complement its current portfolio. The Company had been developing livoletide (AZP-531) as a potential treatment for Prader-Willi syndrome (“PWS”), a rare and complex genetic endocrine disease characterized by hyperphagia, or insatiable hunger. The Company elected to discontinue the development of livoletide as a potential treatment for PWS in April 2020 based upon results from its Phase 2b trial. The Company’s operations to date have focused on conducting preclinical studies and clinical trials, acquiring technology and assets, organization and staffing, business planning, and raising capital. The Company does not have any products approved for sale and has not generated any revenue from product sales. The Company’s product candidates are subject to long development cycles and the Company may be unsuccessful in its efforts to develop, obtain regulatory approval for or market its product candidates. The Company is subject to a number of risks including, but not limited to, the need to obtain adequate additional funding for the ongoing and planned clinical development of its product candidates. Because of the numerous risks and uncertainties associated with pharmaceutical products and development, the Company is unable to accurately predict the timing or amount of funds required to complete development of its product candidates, and costs could exceed the Company’s expectations for a number of reasons, including reasons beyond the Company’s control. Liquidity The Company has incurred net losses since inception and it expects to generate losses from operations for the foreseeable future primarily due to research and development costs for its potential product candidates. As of March 31, 2020, the Company had cash, cash equivalents and restricted cash of $58.9 million and an accumulated deficit of $220.7 million. In December 2019, the Company sold a total of 4,791,667 shares of its common stock pursuant to an underwriting agreement (the “Underwriting Agreement”) with Citigroup Global Markets Inc. and SVB Leerink LLC, as representatives of the several underwriters named herein (the “Underwriters”), for total net proceeds of approximately $26.5 million, after deducting underwriting discounts and commissions and other offering expenses payable by the Company. The price to the public in this offering was $6.00 per share and resulted in the sale of 4,166,667 shares of the Company's common stock for net proceeds of approximately $23.0 million, after deducting underwriting discounts and commissions and other offering expenses payable by the Company. In addition, the Underwriters purchased an additional 625,000 shares of the Company's common stock at the public offering price of $6.00 per share pursuant to a purchase option granted to them under the Underwriting Agreement, resulting in net proceeds of approximately $3.5 million, after deducting underwriting discounts and commissions. In April 2019, the Company entered into an “at-the-market” (“ATM”) equity distribution agreement with Citigroup Global Markets Inc. acting as sole agent with an aggregate offering value of up to $50.0 million, which allows the Company to sell its common stock through the facilities of the Nasdaq Capital Market. Subject to the terms of the ATM equity distribution agreement, the Company is able to determine, at its sole discretion, the timing and number of shares to be sold under this ATM facility. In March 2020, the Company amended and restated the equity distribution agreement to include SVB Leerink LLC as an additional sales agent for the ATM. In March 2020, the Company sold 719,400 shares of its common stock under its ATM equity distribution agreement for net proceeds of approximately $5.7 million. The Company will require additional capital in the future through equity or debt financings, partnerships, collaborations, or other sources to carry out the Company’s planned development activities and to obtain regulatory approval for or to commercialize its product candidates. If additional capital is not secured when required, the Company may need to delay or curtail its operations until such funding is received. Various internal and external factors will affect whether and when the Company’s product candidates become approved drugs. The regulatory approval and market acceptance of the Company’s proposed future products (if any), length of time and cost of developing and commercializing these product candidates and/or failure of them at any stage of the drug approval process will materially affect the Company’s financial condition and future operations. The Company believes its cash, cash equivalents and restricted cash at March 31, 2020 are sufficient to fund its current operations for at least 12 months following the issuance of these financial statements.