Nature of Business	6 Months Ended
Jun. 30, 2018
Nature of Business
Nature of Business	1. Nature of Business Rhythm Pharmaceuticals, Inc. (the “Company”), is a biopharmaceutical company focused on the development and commercialization of therapeutics for the treatment of rare genetic disorders that result in severe, life‑threatening metabolic disorders. The Company's lead product candidate is setmelanotide (“RM‑493”), which is a potent, first‑in‑class, melanocortin‑4, or MC4, receptor, agonist peptide for the treatment of rare genetic disorders of obesity caused by MC4 pathway deficiencies. MC4 pathway deficiencies result in the disruption of satiety signals and energy homeostasis in the body, which, in turn, leads to intense feelings of hunger and to obesity. The Company is currently evaluating setmelanotide for the treatment of six single gene related, or monogenic, MC4 pathway deficiencies: pro‑opiomelanocortin, or POMC, leptin receptor, or LepR, Bardet‑Biedl syndrome, Alström syndrome, POMC heterozygous, and POMC epigenetic disorders for which there are currently no effective or approved treatments. The Company believes that the MC4 pathway is a compelling target for treating these genetic disorders because of its critical role in regulating appetite and weight by promoting satiety and weight control, and that peptide therapeutics are uniquely suited for activating this target. In March 2018 the Company acquired exclusive, worldwide rights from Takeda Pharmaceutical Company Limited (“Takeda”) to develop and commercialize T-3525770 (now “RM-853”). RM-853 is a potent, orally available ghrelin o-acyltransferase (“GOAT”) inhibitor currently in preclinical development for Prader-Willi Syndrome (“PWS”). PWS is a rare genetic disorder that results in hyperphagia and early-onset, life-threatening obesity, for which there are no approved therapeutic options. Corporate Reorganization The Company is a Delaware corporation organized in February 2013 under the name Rhythm Metabolic, Inc. Prior to the Company's organization and the Corporate Reorganization referred to below, the Company was part of Rhythm Pharmaceuticals, Inc. (the “Predecessor Company”), a Delaware corporation which was organized in November 2008 and which commenced active operations in 2010. In March 2013, the Predecessor Company underwent a corporate reorganization, (the “Corporate Reorganization”), pursuant to which all of the outstanding equity securities of the Predecessor Company were exchanged for units of Rhythm Holding Company, LLC, a newly‑organized limited liability company (the “LLC entity”). After the consummation of this exchange and as part of the Corporate Reorganization, the Predecessor Company contributed setmelanotide and the MC4R agonist program to the Company and distributed to the LLC entity all of the then issued and outstanding shares of the Company's stock. The result of the Corporate Reorganization was that the Company and the Predecessor Company became wholly‑owned subsidiaries of the LLC entity and the two product candidates and related programs that were originally held by the Predecessor Company were separated, with relamorelin and the ghrelin agonist program being retained by the Predecessor Company and setmelanotide and the MC4R agonist program being held by the Company. The Predecessor Company, after consummation of the Corporate Reorganization, is referred to within these Notes to Financial Statements as the Relamorelin Company and/or Motus. On October 13, 2015, the Relamorelin Company changed its name to Motus Therapeutics, Inc. (“Motus”) and the Company changed its name to Rhythm Pharmaceuticals, Inc. On December 15, 2016, Motus was sold to a large pharmaceutical company. On August 21, 2017, the LLC entity distributed to its members all of its shares of the Company (see Note 5 for further discussion). Liquidity The Company has incurred operating losses and negative cash flows from operations since inception. As of June 30, 2018, the Company had an accumulated deficit of $141,123. The Company has primarily funded these losses through capital contributions received from the LLC entity and the sale of preferred and common stock to outside investors. To date, the Company has no product revenue and management expects operating losses to continue for the foreseeable future. The Company has devoted substantially all of its resources to its drug development efforts, comprising research and development, manufacturing, conducting clinical trials for its product candidates, protecting its intellectual property and general and administrative functions relating to these operations. The future success of the Company is dependent on its ability to develop its product candidates and ultimately upon its ability to attain profitable operations. At June 30, 2018, the Company had $287,554 of cash and cash equivalents and short‑term investments on hand, which reflects the $163,034 of net proceeds received in June 2018 from the sale of common stock. In the future, the Company will be dependent on obtaining funding from third parties, such as proceeds from the issuance of debt, sale of equity, and funded research and development programs, to maintain the Company's operations and meet the Company's obligations. There is no guarantee that additional equity or other financings will be available to the Company on acceptable terms, or at all. If the Company fails to obtain additional funding when needed, the Company would be forced to scale back, terminate its operations or seek to merge with or be acquired by another company. Management believes that the Company's existing cash resources will be sufficient to fund the Company's operating plan into the second half of 2020.

1. Nature of Business

Rhythm Pharmaceuticals, Inc. (the “Company”), is a biopharmaceutical company focused on the development and commercialization of therapeutics for the treatment of rare genetic disorders that result in severe, life‑threatening metabolic disorders. The Company's lead product candidate is setmelanotide (“RM‑493”), which is a potent, first‑in‑class, melanocortin‑4, or MC4, receptor, agonist peptide for the treatment of rare genetic disorders of obesity caused by MC4 pathway deficiencies. MC4 pathway deficiencies result in the disruption of satiety signals and energy homeostasis in the body, which, in turn, leads to intense feelings of hunger and to obesity. The Company is currently evaluating setmelanotide for the treatment of six single gene related, or monogenic, MC4 pathway deficiencies: pro‑opiomelanocortin, or POMC, leptin receptor, or LepR, Bardet‑Biedl syndrome, Alström syndrome, POMC heterozygous, and POMC epigenetic disorders for which there are currently no effective or approved treatments. The Company believes that the MC4 pathway is a compelling target for treating these genetic disorders because of its critical role in regulating appetite and weight by promoting satiety and weight control, and that peptide therapeutics are uniquely suited for activating this target.

In March 2018 the Company acquired exclusive, worldwide rights from Takeda Pharmaceutical Company Limited (“Takeda”) to develop and commercialize T-3525770 (now “RM-853”). RM-853 is a potent, orally available ghrelin o-acyltransferase (“GOAT”) inhibitor currently in preclinical development for Prader-Willi Syndrome (“PWS”). PWS is a rare genetic disorder that results in hyperphagia and early-onset, life-threatening obesity, for which there are no approved therapeutic options.

Corporate Reorganization

The Company is a Delaware corporation organized in February 2013 under the name Rhythm Metabolic, Inc. Prior to the Company's organization and the Corporate Reorganization referred to below, the Company was part of Rhythm Pharmaceuticals, Inc. (the “Predecessor Company”), a Delaware corporation which was organized in November 2008 and which commenced active operations in 2010.

In March 2013, the Predecessor Company underwent a corporate reorganization, (the “Corporate Reorganization”), pursuant to which all of the outstanding equity securities of the Predecessor Company were exchanged for units of Rhythm Holding Company, LLC, a newly‑organized limited liability company (the “LLC entity”). After the consummation of this exchange and as part of the Corporate Reorganization, the Predecessor Company contributed setmelanotide and the MC4R agonist program to the Company and distributed to the LLC entity all of the then issued and outstanding shares of the Company's stock. The result of the Corporate Reorganization was that the Company and the Predecessor Company became wholly‑owned subsidiaries of the LLC entity and the two product candidates and related programs that were originally held by the Predecessor Company were separated, with relamorelin and the ghrelin agonist program being retained by the Predecessor Company and setmelanotide and the MC4R agonist program being held by the Company. The Predecessor Company, after consummation of the Corporate Reorganization, is referred to within these Notes to Financial Statements as the Relamorelin Company and/or Motus.

On October 13, 2015, the Relamorelin Company changed its name to Motus Therapeutics, Inc. (“Motus”) and the Company changed its name to Rhythm Pharmaceuticals, Inc. On December 15, 2016, Motus was sold to a large pharmaceutical company. On August 21, 2017, the LLC entity distributed to its members all of its shares of the Company (see Note 5 for further discussion).

Liquidity

The Company has incurred operating losses and negative cash flows from operations since inception. As of June 30, 2018, the Company had an accumulated deficit of $141,123. The Company has primarily funded these losses through capital contributions received from the LLC entity and the sale of preferred and common stock to outside investors. To date, the Company has no product revenue and management expects operating losses to continue for the foreseeable future. The Company has devoted substantially all of its resources to its drug development efforts, comprising research and development, manufacturing, conducting clinical trials for its product candidates, protecting its intellectual property and general and administrative functions relating to these operations. The future success of the Company is dependent on its ability to develop its product candidates and ultimately upon its ability to attain profitable operations. At June 30, 2018, the Company had $287,554 of cash and cash equivalents and short‑term investments on hand, which reflects the $163,034 of net proceeds received in June 2018 from the sale of common stock. In the future, the Company will be dependent on obtaining funding from third parties, such as proceeds from the issuance of debt, sale of equity, and funded research and development programs, to maintain the Company's operations and meet the Company's obligations. There is no guarantee that additional equity or other financings will be available to the Company on acceptable terms, or at all. If the Company fails to obtain additional funding when needed, the Company would be forced to scale back, terminate its operations or seek to merge with or be acquired by another company. Management believes that the Company's existing cash resources will be sufficient to fund the Company's operating plan into the second half of 2020.