Nature of Business and Basis of Presentation	12 Months Ended
Dec. 31, 2020
Accounting Policies [Abstract]
Nature of Business and Basis of Presentation	(1) Nature of Business and Basis of Presentation Nature of Business Amarin Corporation plc, or Amarin, or the Company, is a pharmaceutical company focused on the commercialization and development of therapeutics to improve cardiovascular health and reduce cardiovascular risk. The Company’s lead product, VASCEPA^® (icosapent ethyl), was first approved by the United States Food and Drug Administration, or FDA, in July 2012 for use as an adjunct to diet to reduce triglyceride, or TG, levels in adult patients with severe (>500 mg/dL) hypertriglyceridemia. In January 2013, the Company launched 1-gram size VASCEPA in the United States, or U.S., and in October 2016, introduced a smaller 0.5-gram capsule size. On December 13, 2019, the FDA approved a new indication and label expansion for VASCEPA based on the results of the Company’s long-term cardiovascular outcomes trial, REDUCE-IT^®, or Reduction of Cardiovascular Events with EPA – Intervention Trial. VASCEPA is approved by the FDA as an adjunct to maximally tolerated statin therapy for reducing persistent cardiovascular risk in select high risk patients. VASCEPA is also available for sale by prescription only in Canada, Lebanon and the United Arab Emirates through collaborations and is also in development in other jurisdictions. On March 30, 2020, the United States District Court for the District of Nevada, or the Nevada Court, ruled in favor of two generics companies in Amarin’s patent litigation related to its abbreviated new drug applications, or ANDAs, that seek FDA approval for sale of generic versions of VASCEPA for the original indication of VASCEPA as an adjunct to diet to reduce TG levels in adult patients with severe (>500 mg/dL) hypertriglyceridemia. On May 22, 2020 and August 10, 2020, the two generics companies, Hikma Pharmaceutical USA Inc., or Hikma, and Dr. Reddy’s Laboratories, Inc., or Dr. Reddy’s, respectively, received FDA approval to market its generic versions of VASCEPA. On September 3, 2020, the U.S. Court of Appeals for the Federal Circuit, or the Federal Circuit, upheld the March ruling by the Nevada Court in favor of the two generics companies. On October 2, 2020, the Company filed a combined petition for panel rehearing or rehearing en banc. On November 4, 2020, the Company’s rehearing and en banc petitions were denied. On February 11, 2021, Amarin filed a petition for a writ of certiorari with the United States Supreme Court to ask the Court to hear the Company’s appeal in this litigation. In August 2020, the Company announced plans to launch icosapent ethyl under the brand name VAZKEPA^®, hereinafter along with the U.S. brand name VASCEPA, collectively referred to as VASCEPA, in major markets in Europe through the Company’s new European sales and marketing teams. On January 29, 2021, the Committee for Medicinal Products for Human Use, or CHMP, of the European Medicines Agency, or EMA, adopted a positive opinion, recommending that a marketing authorization be granted to icosapent ethyl in the European Union, or EU, for the reduction of risk of cardiovascular events in patients at high cardiovascular risk. The CHMP recommendation is now expected to be reviewed by the European Community, or EC, with a decision expected to take place within 67 days of the CHMP opinion. In November 2020, the Company announced topline results from the Phase 3 clinical trial of VASCEPA conducted by the Company’s partner in China. On February 9, 2021, the Company announced that regulatory review processes for approval of VASCEPA in Mainland China and Hong Kong have commenced. The Chinese National Medical Products Administration, or NMPA, has accepted for review the new drug application for VASCEPA based on the results from the Phase 3 clinical trial and the results from the Company’s prior studies of VASCEPA. The Hong Kong Department of Health is evaluating VASCEPA based on current approvals in the United States and Canada. The Company currently has strategic collaborations to develop and commercialize VASCEPA in select territories outside the United States. Amarin is responsible for supplying VASCEPA to all markets in which the product is sold, including in Canada, Lebanon and the United Arab Emirates where the drug is promoted and sold via collaboration with third-party companies that compensate Amarin for such supply. Amarin is not responsible for providing any generic company with drug product. The Company operates in one business segment. Basis of Presentation The consolidated financial statements included herein have been prepared by the Company in accordance with accounting principles generally accepted in the United States and pursuant to the rules and regulations of the Securities and Exchange Commission, or the SEC. The consolidated financial statements reflect all adjustments of a normal and recurring nature that, in the opinion of management, are necessary to present fairly the Company’s financial position, results of operations and cash flows for the periods indicated. The preparation of the Company’s consolidated financial statements in conformity with U.S. Generally Accepted Accounting Principles, or GAAP, requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenues and expenses during the reporting period. The results of operations for the years ended December 31, 2020, 2019 and 2018 are not necessarily indicative of the results for any future period. Certain numbers presented throughout this document may not add precisely to the totals provided due to rounding. Absolute and percentage changes are calculated using the underlying amounts in thousands. The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation. The accompanying consolidated financial statements of the Company and subsidiaries have been prepared on a basis which assumes that the Company will continue as a going concern, which contemplates the realization of assets and the satisfaction of liabilities and commitments in the normal course of business, as well as the current global pandemic, COVID-19. At December 31, 2020, the Company had Total assets of $966.0 million, of which $563.4 million consisted of cash and liquid short-term and long-term investments. More specifically, the Company had Current assets of $879.2 million, including Cash and cash equivalents of $187.0 million, Short-term investments of $314.0 million, Accounts receivable, net, of $154.6 million and Inventory of $188.9 million. In addition, at December 31, 2020, the Company had Long-term investments of $62.5 million. At December 31, 2020, the Company had no debt outstanding.

Nature of Business and Basis of Presentation

12 Months Ended

Dec. 31, 2020

Nature of Business and Basis of Presentation

(1) Nature of Business and Basis of Presentation

Nature of Business

Amarin Corporation plc, or Amarin, or the Company, is a pharmaceutical company focused on the commercialization and development of therapeutics to improve cardiovascular health and reduce cardiovascular risk.

The Company’s lead product, VASCEPA^® (icosapent ethyl), was first approved by the United States Food and Drug Administration, or FDA, in July 2012 for use as an adjunct to diet to reduce triglyceride, or TG, levels in adult patients with severe (>500 mg/dL) hypertriglyceridemia. In January 2013, the Company launched 1-gram size VASCEPA in the United States, or U.S., and in October 2016, introduced a smaller 0.5-gram capsule size. On December 13, 2019, the FDA approved a new indication and label expansion for VASCEPA based on the results of the Company’s long-term cardiovascular outcomes trial, REDUCE-IT^®, or Reduction of Cardiovascular Events with EPA – Intervention Trial. VASCEPA is approved by the FDA as an adjunct to maximally tolerated statin therapy for reducing persistent cardiovascular risk in select high risk patients. VASCEPA is also available for sale by prescription only in Canada, Lebanon and the United Arab Emirates through collaborations and is also in development in other jurisdictions.

On March 30, 2020, the United States District Court for the District of Nevada, or the Nevada Court, ruled in favor of two generics companies in Amarin’s patent litigation related to its abbreviated new drug applications, or ANDAs, that seek FDA approval for sale of generic versions of VASCEPA for the original indication of VASCEPA as an adjunct to diet to reduce TG levels in adult patients with severe (>500 mg/dL) hypertriglyceridemia. On May 22, 2020 and August 10, 2020, the two generics companies, Hikma Pharmaceutical USA Inc., or Hikma, and Dr. Reddy’s Laboratories, Inc., or Dr. Reddy’s, respectively, received FDA approval to market its generic versions of VASCEPA. On September 3, 2020, the U.S. Court of Appeals for the Federal Circuit, or the Federal Circuit, upheld the March ruling by the Nevada Court in favor of the two generics companies. On October 2, 2020, the Company filed a combined petition for panel rehearing or rehearing en banc. On November 4, 2020, the Company’s rehearing and en banc petitions were denied. On February 11, 2021, Amarin filed a petition for a writ of certiorari with the United States Supreme Court to ask the Court to hear the Company’s appeal in this litigation.

In August 2020, the Company announced plans to launch icosapent ethyl under the brand name VAZKEPA^®, hereinafter along with the U.S. brand name VASCEPA, collectively referred to as VASCEPA, in major markets in Europe through the Company’s new European sales and marketing teams. On January 29, 2021, the Committee for Medicinal Products for Human Use, or CHMP, of the European Medicines Agency, or EMA, adopted a positive opinion, recommending that a marketing authorization be granted to icosapent ethyl in the European Union, or EU, for the reduction of risk of cardiovascular events in patients at high cardiovascular risk. The CHMP recommendation is now expected to be reviewed by the European Community, or EC, with a decision expected to take place within 67 days of the CHMP opinion.

In November 2020, the Company announced topline results from the Phase 3 clinical trial of VASCEPA conducted by the Company’s partner in China. On February 9, 2021, the Company announced that regulatory review processes for approval of VASCEPA in Mainland China and Hong Kong have commenced. The Chinese National Medical Products Administration, or NMPA, has accepted for review the new drug application for VASCEPA based on the results from the Phase 3 clinical trial and the results from the Company’s prior studies of VASCEPA. The Hong Kong Department of Health is evaluating VASCEPA based on current approvals in the United States and Canada.

The Company currently has strategic collaborations to develop and commercialize VASCEPA in select territories outside the United States. Amarin is responsible for supplying VASCEPA to all markets in which the product is sold, including in Canada, Lebanon and the United Arab Emirates where the drug is promoted and sold via collaboration with third-party companies that compensate Amarin for such supply. Amarin is not responsible for providing any generic company with drug product. The Company operates in one business segment.

Basis of Presentation

The consolidated financial statements included herein have been prepared by the Company in accordance with accounting principles generally accepted in the United States and pursuant to the rules and regulations of the Securities and Exchange Commission, or the SEC.

The consolidated financial statements reflect all adjustments of a normal and recurring nature that, in the opinion of management, are necessary to present fairly the Company’s financial position, results of operations and cash flows for the periods indicated. The preparation of the Company’s consolidated financial statements in conformity with U.S. Generally Accepted Accounting Principles, or

GAAP, requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenues and expenses during the reporting period. The results of operations for the years ended December 31, 2020, 2019 and 2018 are not necessarily indicative of the results for any future period. Certain numbers presented throughout this document may not add precisely to the totals provided due to rounding. Absolute and percentage changes are calculated using the underlying amounts in thousands. The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation.

The accompanying consolidated financial statements of the Company and subsidiaries have been prepared on a basis which assumes that the Company will continue as a going concern, which contemplates the realization of assets and the satisfaction of liabilities and commitments in the normal course of business, as well as the current global pandemic, COVID-19.

At December 31, 2020, the Company had Total assets of $966.0 million, of which $563.4 million consisted of cash and liquid short-term and long-term investments. More specifically, the Company had Current assets of $879.2 million, including Cash and cash equivalents of $187.0 million, Short-term investments of $314.0 million, Accounts receivable, net, of $154.6 million and Inventory of $188.9 million. In addition, at December 31, 2020, the Company had Long-term investments of $62.5 million. At December 31, 2020, the Company had no debt outstanding.