On Mar. 14th, 2024, resmetirom (REZDIFFRA™) became the first and only medicine approved by the FDA for the treatment of NASH/MASH (non-alcoholic steatohepatitis, NASH; metabolic dysfunction-associated steatohepatitis, MASH). Resmetirom, an oral, liver-targeting, once-daily THR-β-selective agonist originally discovered at Roche Nutley, was first highlighted as a Molecule of the Month in Dec. 2022. Now, with the FDA’s accelerated approval, this 2023 Molecule of the Year nominee reflects a historic milestone for liver drug discovery. This article reviews how the molecule works, how it was discovered, and why it’s a big deal.