Is resmetirom (Rezdiffra) the first FDA-approved drug for MASH?

Yes. In March 2024, the FDA granted accelerated approval to resmetirom, making it the first drug specifically approved for MASH (previously called NASH) with moderate-to-advanced hepatic fibrosis (stages F2-F3). All prior pharmacotherapy was off-label.

What were the primary endpoints of MAESTRO-NASH?

The trial had two co-primary endpoints at 52 weeks: (1) NASH resolution without worsening of fibrosis, and (2) at least one-stage improvement in fibrosis without worsening of NAS (NAFLD Activity Score). Both were assessed by paired liver biopsies read by a central pathology panel.

How large was the treatment effect of resmetirom over placebo?

For NASH resolution, the 100 mg dose achieved a 19.4 percentage-point advantage over placebo (29.9% vs. 9.7%). For fibrosis improvement, the advantage was 11.3 percentage points (25.9% vs. 14.2%). These are statistically significant but modest in absolute terms.

Does resmetirom work for patients with cirrhosis (F4 fibrosis)?

The primary MAESTRO-NASH analysis excluded F4 patients, and the FDA approval is limited to F2-F3 fibrosis. Ongoing studies include some compensated cirrhosis patients, but prescribing for F4 disease is currently off-label and unsupported by controlled data.

Can resmetirom be combined with GLP-1 receptor agonists like semaglutide?

There is no controlled trial evaluating this combination. The mechanisms are complementary (THR-β agonism vs. incretin pathway), and patients on GLP-1 agonists were not excluded from MAESTRO-NASH, but formal combination efficacy and safety data are lacking.

What are the most common side effects of resmetirom?

Diarrhea (27% at 100 mg) and nausea (19% at 100 mg) were most frequent, typically mild-to-moderate and concentrated in the first 12 weeks. The FDA label also warns about potential drug-induced liver injury and interactions with OATP1B1/1B3 substrates including certain statins.

Do patients need a liver biopsy to receive resmetirom?

The FDA label specifies biopsy-confirmed MASH with F2-F3 fibrosis. Prescribing based solely on non-invasive testing (FibroScan, FIB-4) is technically off-label, though clinical practice may evolve as non-invasive biomarkers gain validation.

What happens if the confirmatory outcomes trial fails?

Resmetirom was approved under the FDA's accelerated approval pathway based on histological surrogates. If the confirmatory MAESTRO-OUTCOMES trial does not demonstrate reduced clinical events (cirrhosis progression, liver-related death, transplant), the FDA can withdraw the approval.

How much does Rezdiffra cost?

The wholesale acquisition cost is approximately $47,000 per year. Insurance coverage requires prior authorization in most cases, and many plans require documentation of biopsy confirmation, fibrosis staging, and failed lifestyle intervention before approving coverage.

Which clinical guidelines now include resmetirom?

The AASLD and AGA have updated their practice guidance to include resmetirom for biopsy-confirmed MASH with F2-F3 fibrosis. European guidelines (EASL) have been slower to incorporate it. No major guideline yet provides a clear sequencing algorithm combining resmetirom with other agents.

What MAESTRO-NASH Actually Changes in Clinical Practice

By HealthRX Medical Team

Published May 25, 2026Updated May 25, 2026Last reviewed May 25, 2026

At a glance

| Detail | Value | |---|---| | Trial name | MAESTRO-NASH (Phase 3) | | N | 966 randomized | | Intervention | Resmetirom 80 mg or 100 mg daily (oral) | | Comparator | Placebo | | Duration | 52-week primary analysis (ongoing to 54 months) | | Primary endpoints | (1) NASH resolution with no worsening of fibrosis; (2) ≥1-stage fibrosis improvement with no worsening of NAS | | Key result | Both doses met both co-primary endpoints (p < 0.001 for all comparisons vs placebo) |

The Prescribing Gap Before MAESTRO-NASH

Before March 2024, clinicians managing MASH had no FDA-approved pharmacotherapy. The standard of care was weight loss through lifestyle modification, bariatric surgery referral for eligible patients, and off-label use of pioglitazone or vitamin E for select cases. GLP-1 receptor agonists (semaglutide in particular) showed promise in phase 2 data but lacked MASH-specific approval. Hepatologists and endocrinologists were left managing a progressive fibrotic liver disease with tools that were either indirect or unapproved for the indication.

That gap matters because MASH affects an estimated 6-8 million Americans with significant fibrosis (stages F2-F3), the population at highest risk for progression to cirrhosis and liver-related mortality. The absence of a labeled therapy meant no insurance pathway, no standardized prescribing algorithm, and no anchoring drug around which to build combination strategies.

What the Trial Actually Tested

MAESTRO-NASH enrolled adults with biopsy-confirmed MASH and fibrosis stages F1B through F3, though the primary efficacy analysis focused on the F2-F3 subgroup (n = 888). This is a critical design detail that many summaries gloss over. The FDA approval mirrors this restriction: Rezdiffra is indicated for MASH with moderate-to-advanced (F2-F3) hepatic fibrosis, not for the full MASH spectrum.

The HealthRX Clinical-Translation Framework for MAESTRO-NASH

We assess practice-changing trials across four dimensions: (1) endpoint validity, (2) population generalizability, (3) guideline integration speed, and (4) real-world prescribing friction. MAESTRO-NASH scores high on the first two but exposes significant challenges on the latter.

Endpoint validity. The co-primary endpoints (histological NASH resolution and fibrosis improvement) required paired liver biopsies at baseline and week 52. This is the gold standard for MASH trials, and the FDA accepted these as reasonably likely to predict clinical benefit under accelerated approval. The trial used a central pathology reading panel with predefined scoring criteria (NAS and fibrosis staging per the NASH CRN system). The accelerated approval pathway means a confirmatory outcomes trial demonstrating reduced progression to cirrhosis or liver-related events is still required.

Population generalizability. The trial population was approximately 56% female, had a mean BMI of 36 kg/m², mean age of 56, and roughly 75% white. About 67% had type 2 diabetes. Patients with decompensated cirrhosis (F4), uncontrolled hypothyroidism, or recent bariatric surgery were excluded. These exclusions define who the data actually speak to, and who remains a clinical judgment call.

Results Beyond the Topline

The headline numbers deserve unpacking.

NASH Resolution (Co-Primary Endpoint 1)

| Group | NASH Resolution (%) | Difference vs Placebo | p-value | |---|---|---|---| | Resmetirom 80 mg | 25.9% | +15.4 pp | <0.001 | | Resmetirom 100 mg | 29.9% | +19.4 pp | <0.001 | | Placebo | 9.7% |, |, |

Fibrosis Improvement (Co-Primary Endpoint 2)

| Group | ≥1-Stage Improvement (%) | Difference vs Placebo | p-value | |---|---|---|---| | Resmetirom 80 mg | 24.2% | +9.6 pp | <0.001 | | Resmetirom 100 mg | 25.9% | +11.3 pp | <0.001 | | Placebo | 14.2% |, |, |

The placebo fibrosis improvement rate of 14.2% is worth noting. Spontaneous histological improvement on biopsy is a known phenomenon in MASH trials, driven partly by regression to the mean and sampling variability in liver biopsy. The treatment effect over placebo for fibrosis (roughly 10-11 percentage points) is real but modest in absolute terms.

Secondary endpoints showed marked LDL cholesterol reductions (approximately 14-18% beyond placebo), triglyceride lowering, and improvements in liver enzyme levels. Resmetirom is a selective thyroid hormone receptor-beta (THR-β) agonist, so these lipid effects are mechanistically expected and pharmacologically distinct from statins.

Safety Profile in Practice

Diarrhea and nausea were the most common adverse events, occurring in 27% and 19% of the 100 mg group versus 16% and 10% on placebo. Most GI events were mild-to-moderate and concentrated in the first 12 weeks. The FDA label carries specific warnings about drug-induced liver injury and recommends hepatic monitoring, though serious hepatotoxicity was rare in the trial.

A practical concern the label addresses: resmetirom interacts with drugs that undergo OATP1B1/1B3 transport (certain statins, for example). Given that the MASH population is heavily co-medicated with statins, this interaction requires dose adjustments. Clinicians prescribing Rezdiffra alongside rosuvastatin or atorvastatin must check recommended limits.

Thyroid function remained stable in trial participants. The THR-β selectivity means minimal impact on heart rate, bone density, or other THR-α-mediated effects, which was a key theoretical advantage over non-selective thyroid hormone analogs.

Which Guidelines Have Actually Updated

The AASLD published updated practice guidance in 2023-2024 that acknowledged the shifting therapeutic pipeline for MASH but preceded the FDA approval. Since the March 2024 approval, the AASLD has incorporated resmetirom into its clinical guidance for patients with biopsy-confirmed MASH and F2-F3 fibrosis, positioning it as the first-line pharmacotherapy option for this population.

The American Gastroenterological Association (AGA) similarly updated its clinical practice update to include resmetirom, noting that it does not replace weight management but adds a pharmacologic layer for fibrotic disease. European guidelines (EASL) have been slower to incorporate Rezdiffra given that EMA approval followed a different timeline.

A practical gap persists: no major guideline yet offers a clear algorithm for sequencing resmetirom with GLP-1 agonists, pioglitazone, or vitamin E. Clinicians are making these combination decisions empirically.

What This Means for Patients Who Don't Match the Trial

Several common clinical scenarios fall outside the trial's evidence base.

F1 fibrosis. The approval is limited to F2-F3. Patients with early fibrosis (F1) are not covered by the label. Whether to treat early is an unresolved question; the MAESTRO-NASH data cannot answer it directly.

F4 / compensated cirrhosis. Excluded from the primary analysis. The ongoing MAESTRO-NAFLD-1 study includes some compensated cirrhosis patients and will provide longer-term outcomes data, but current prescribing for F4 patients is off-label.

Patients without biopsy. The approval requires biopsy-confirmed MASH. In practice, many patients are diagnosed via non-invasive testing (FibroScan, FIB-4 index, ELF score). Prescribing Rezdiffra without biopsy confirmation is technically off-label, though real-world use will likely push this boundary as non-invasive biomarkers improve.

Lean MASH (BMI < 25). The trial population had a mean BMI of 36. Lean MASH patients, who represent roughly 10-20% of the MASH population, were underrepresented. Efficacy in this group is unknown.

Concurrent GLP-1 use. Patients on semaglutide or tirzepatide were not excluded from MAESTRO-NASH, but the trial was not designed to evaluate combination therapy. The mechanistic rationale for combining a THR-β agonist with a GLP-1 agonist is strong (different pathways, complementary metabolic effects), but controlled data are lacking.

The Accelerated Approval Question

Resmetirom received accelerated approval based on histological surrogate endpoints, not clinical outcomes like reduced mortality or decreased progression to liver transplant. The confirmatory MAESTRO-OUTCOMES trial must demonstrate that histological improvement translates into fewer clinical events. If it fails, the approval can be withdrawn.

This matters for clinical practice because it introduces uncertainty. Prescribers are betting on a surrogate, not a proven clinical outcome. The parallel to the eteplirsen (Duchenne muscular dystrophy) and aducanumab (Alzheimer's) accelerated approvals is instructive: surrogate endpoints do not always predict clinical benefit. The counterargument is that the histological endpoints used in MAESTRO-NASH (NASH resolution and fibrosis regression) have stronger face validity and natural-history data supporting their link to outcomes than some prior accelerated approvals.

Cost and Access Realities

Rezdiffra launched at a wholesale acquisition cost of approximately $47,000 per year. Insurance coverage has been inconsistent. Many commercial plans require prior authorization with documentation of biopsy-confirmed MASH, fibrosis staging, and evidence of failed lifestyle intervention. Medicare Part D coverage varies by plan.

The cost creates a practical barrier to the prescribing shift the trial data would otherwise support. For a disease affecting millions with fibrotic MASH, the gap between clinical evidence and accessible treatment remains wide. Patient assistance programs from Madrigal Pharmaceuticals exist but do not fully close this gap.

Limitations the Authors Acknowledged

The trial publication explicitly notes several limitations. The 52-week biopsy timepoint captures histological change but does not demonstrate durability. Liver biopsy has inherent sampling error (a single biopsy samples roughly 1/50,000th of the liver). The population was predominantly white, limiting generalizability to other ethnic groups, particularly Hispanic populations who carry a disproportionate MASH burden. The ongoing long-term extension will address some of these gaps but results are years away.

Frequently asked questions

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References

Harrison SA, Bedossa P, Guy CD, et al. A Phase 3, Randomized, Controlled Trial of Resmetirom in NASH with Liver Fibrosis. N Engl J Med. 2024;390(6):497-509. PubMed
U.S. FDA. Rezdiffra (resmetirom) prescribing information. 2024. FDA Label
Rinella ME, Neuschwander-Tetri BA, Siddiqui MS, et al. AASLD Practice Guidance on the Clinical Assessment and Management of Nonalcoholic Fatty Liver Disease. Hepatology. 2023;77(5):1797-1835. PubMed
Harrison SA, Taub R, Neff GW, et al. Resmetirom for nonalcoholic fatty liver disease: a randomized, double-blind, placebo-controlled phase 2 trial. Hepatology. 2023;78(5):1525-1537. PubMed
Newsome PN, Buchholtz K, Cusi K, et al. A Placebo-Controlled Trial of Subcutaneous Semaglutide in Nonalcoholic Steatohepatitis. N Engl J Med. 2021;384(12):1113-1124. PubMed