Resmetirom for MASH: How the First Approved Fatty Liver

What Is Resmetirom and Why Is It Considered a Breakthrough?

Resmetirom, sold under the brand name Rezdiffra by Madrigal Pharmaceuticals, is a selective thyroid hormone receptor-beta (THR-beta) agonist that acts primarily in the liver to reduce hepatic fat accumulation and improve markers of liver fibrosis. The FDA granted accelerated approval in March 2024 for adults with non-cirrhotic MASH and moderate to advanced fibrosis, used alongside diet and exercise. Until this approval, clinicians caring for patients with MASH — formerly known as non-alcoholic steatohepatitis (NASH) — had no licensed disease-specific therapy and had to rely on weight loss, glycemic control, and management of comorbidities.

The approval was supported by the Phase 3 MAESTRO-NASH trial, which evaluated liver biopsy endpoints including MASH resolution and fibrosis improvement. By selectively engaging the THR-beta receptor in hepatocytes, resmetirom is designed to mimic the metabolic effects of thyroid hormone in the liver without producing the cardiovascular or skeletal side effects associated with broader thyroid stimulation. Hepatology societies, including the American Association for the Study of Liver Diseases (AASLD), have begun integrating resmetirom into updated practice guidance for selecting patients with significant fibrosis who may benefit from pharmacotherapy.

Which Patients Are Candidates for MASH Treatment in 2026?

MASH sits within the broader spectrum of metabolic dysfunction-associated steatotic liver disease (MASLD), a condition closely linked to obesity, type 2 diabetes, and cardiometabolic risk. Public health data from the National Institutes of Health and AASLD indicate that MASLD now affects a substantial proportion of adults in high-income countries, with a meaningful subset progressing to MASH and fibrosis that raises the risk of cirrhosis, liver failure, and hepatocellular carcinoma. Identifying which patients should receive pharmacotherapy depends on staging fibrosis, traditionally via biopsy but increasingly through non-invasive tests such as FibroScan, ELF scoring, and MRI-based elastography.

Hepatologists generally reserve resmetirom for patients with stage F2 to F3 fibrosis, excluding those with decompensated cirrhosis, in whom safety has not been established. Because many candidates also have type 2 diabetes or obesity, clinicians are increasingly combining MASH care with GLP-1 receptor agonist therapy, which independently improves hepatic steatosis. As access expands in 2026 through broader payer coverage and clinician familiarity, more primary care physicians and endocrinologists are referring patients with elevated liver enzymes and metabolic risk factors for hepatology assessment rather than waiting for symptomatic disease.

What Are the Side Effects and Monitoring Requirements?

In the MAESTRO-NASH program, the most frequently reported adverse events with resmetirom included diarrhea and nausea, typically mild to moderate and most pronounced in the early weeks of therapy. The FDA prescribing information advises clinicians to monitor liver enzymes at baseline and during treatment, and to be alert for potential drug-induced liver injury, gallbladder-related adverse events, and interactions with statins. Because resmetirom is metabolized through cytochrome P450 enzymes, drug-drug interactions with commonly co-prescribed medications in MASH patients — including certain statins and antidiabetic agents — require attention.

Long-term outcome data, including effects on cirrhosis progression, liver-related morbidity, and mortality, are still being collected through ongoing trials and post-marketing surveillance. The accelerated approval pathway used for resmetirom requires Madrigal to confirm clinical benefit in continued studies. For now, hepatology guidance emphasizes shared decision-making, careful patient selection, and integration with lifestyle interventions and management of metabolic comorbidities rather than viewing the drug as a stand-alone solution.