Resmetirom (Rezdiffr™) is an oral thyroid hormone receptor-β (THR-β) agonist developed by Madrigal Pharmaceuticals, Inc., to treat metabolic dysfunction-associated steatohepatitis (MASH), previously known as nonalcoholic steatohepatitis (NASH). On March 14, 2024, resmetirom received its first approval in the USA for the treatment of adults with noncirrhotic NASH and moderate to advanced liver fibrosis (F2 to F3 fibrosis), in conjunction with diet and exercise. The approval was under accelerated approval. Resmetirom is also undergoing regulatory review in the EU for the treatment of MASH/NASH. This summary outlines the key milestones in resmetirom's development leading to this first approval. The information presented here reflects the opinions of the author. For a complete list of declarations, including funding and author disclosure statements, and copyright information, please refer to the full text online. © Springer Nature Switzerland AG 2024.Resmetirom (Rezdiffr™) is an oral thyroid hormone receptor-β (THR-β) agonist developed by Madrigal Pharmaceuticals, Inc., to treat metabolic dysfunction-associated steatohepatitis (MASH), previously known as nonalcoholic steatohepatitis (NASH). On March 14, 2024, resmetirom received its first approval in the USA for the treatment of adults with noncirrhotic NASH and moderate to advanced liver fibrosis (F2 to F3 fibrosis), in conjunction with diet and exercise. The approval was under accelerated approval. Resmetirom is also undergoing regulatory review in the EU for the treatment of MASH/NASH. This summary outlines the key milestones in resmetirom's development leading to this first approval. The information presented here reflects the opinions of the author. For a complete list of declarations, including funding and author disclosure statements, and copyright information, please refer to the full text online. © Springer Nature Switzerland AG 2024.