Retatrutide for MASH and MASLD: What the Phase 2a Liver-Fat Data Show

The honest answer: Retatrutide is not FDA-approved for MASH, MASLD, or anything else. The only human data in fatty liver disease is a single Phase 2a substudy (n=98) measuring liver fat by MRI-PDFF at 24 weeks^[1]. There is no Phase 3 retatrutide-in-MASH trial reported as of 2026-05-25.

At a glance

• Retatrutide is Eli Lilly’s investigational triple GIP/GLP-1/glucagon receptor agonist. It is not approved for any indication, including MASH/MASLD.
• The only human MASLD data is Sanyal et al., Nat Med 2024 (PMID 38858523) — a 48-week Phase 2a substudy in 98 adults with obesity and ≥10% liver fat^[1].
• At 24 weeks, mean relative liver-fat reduction was −42.9% (1 mg), −57.0% (4 mg), −81.4% (8 mg), −82.4% (12 mg) vs +0.3% placebo (all P < 0.001)^[1].
• Liver fat normalization (<5%) at 24 weeks: 27% / 52% / 79% / 86% across the four doses vs 0% placebo^[1].
• The Sanyal Phase 2a used MRI-PDFF, not biopsy. MASH resolution and fibrosis improvement endpoints were not assessed.
• The current FDA-approved option for biopsy-confirmed MASH with F1B–F3 fibrosis is Rezdiffra (resmetirom), approved March 2024^[11]. Semaglutide (Wegovy) was approved for MASH in August 2025 based on ESSENCE Phase 3^[3].
• Compounded retatrutide for MASH is not a legitimate pathway — it is not on the FDA bulk substances list, has no FDA-reviewed safety package, and is in active investigation.

What MASH and MASLD mean

MASLD (metabolic dysfunction-associated steatotic liver disease) is the 2023 nomenclature for what used to be called NAFLD — excess fat accumulation in the liver (≥5% of hepatocytes) in a patient with at least one cardiometabolic risk factor (overweight/obesity, type 2 diabetes, hypertension, dyslipidemia). MASH (metabolic dysfunction-associated steatohepatitis) is the more advanced form: fatty liver plus inflammation and hepatocyte injury (ballooning) on biopsy. MASH can progress through fibrosis stages F1 → F2 → F3 → F4 (cirrhosis), with higher-stage fibrosis driving the liver-related mortality risk. See our Wegovy MASH evidence review for the terminology change in detail and the ESSENCE Phase 3 results.

Where retatrutide stands

Retatrutide is investigational. The Phase 3 obesity program (TRIUMPH) is in flight; TRIUMPH-4 read out in December 2025 for obesity + knee osteoarthritis. There is no dedicated Phase 3 retatrutide-in-MASH trial publicly disclosed as of 2026-05-25. The only human MASLD evidence is the Sanyal Phase 2a substudy nested within the parent obesity Phase 2 program^[1]. For the broader retatrutide evidence base (Phase 2 weight loss, TRIUMPH-4, mechanism, and access considerations), see our retatrutide triple-agonist evidence review and the TRIUMPH-1 before-and-after evidence.

What Sanyal Phase 2a showed

Sanyal et al., Nat Med 2024 (PMID 38858523), reported a randomized, double-blind, placebo-controlled Phase 2a substudy of once-weekly subcutaneous retatrutide in adults with obesity-related MASLD^[1]. Verified design and results:

• Sample size: n = 98 (substudy of the 48-week Phase 2 obesity trial in participants with MASLD and ≥10% liver fat)
• Doses: 1 mg, 4 mg, 8 mg, 12 mg subcutaneously once weekly, or placebo
• Duration: 48 weeks of dosing
• Primary endpoint: mean relative change from baseline in liver fat by MRI-PDFF at 24 weeks

Mean relative change in liver fat at 24 weeks was −42.9% (1 mg), −57.0% (4 mg), −81.4% (8 mg), −82.4% (12 mg) versus +0.3% with placebo (all P < 0.001 vs placebo)^[1]. Liver-fat normalization (defined as <5%) at 24 weeks was achieved by 27% / 52% / 79% / 86% of participants across the four reta arms versus 0% on placebo^[1].

Two important caveats: (1) the primary endpoint was measured by MRI-PDFF, an imaging biomarker for liver fat content, not by paired liver biopsy. MASH resolution and fibrosis improvement — the histologic endpoints the FDA has used to approve resmetirom and semaglutide for MASH — were not assessed. (2) The Phase 2a abstract does not break out adverse-event or discontinuation rates within the MASLD substudy specifically; safety data for the parent obesity Phase 2 are in Jastreboff 2023 NEJM (PMID 37366315).

FDA-approved comparator: resmetirom (Rezdiffra), MAESTRO-NASH

On March 14, 2024 the FDA granted accelerated approval to resmetirom (Rezdiffra), a thyroid hormone receptor-beta agonist, as the first drug ever approved for MASH^[11]. Approval was based on MAESTRO-NASH (Harrison et al., NEJM 2024, PMID 38324483; NCT03900429), a Phase 3 trial of 966 adults with biopsy-confirmed MASH and F1B, F2, or F3 fibrosis^[2].

• NASH resolution with no worsening of fibrosis at week 52: 25.9% (80 mg) / 29.9% (100 mg) vs 9.7% placebo (P < 0.001 for both)^[2]
• Fibrosis improvement ≥1 stage with no worsening of NAFLD activity score: 24.2% (80 mg) / 25.9% (100 mg) vs 14.2% placebo (P < 0.001 for both)^[2]

Resmetirom is currently the only drug approved on a histologic MASH endpoint via paired biopsy. It is indicated for adults with non-cirrhotic MASH and moderate-to-advanced (F2/F3) fibrosis.

Cross-trial vs semaglutide ESSENCE Phase 3

Sanyal et al., NEJM 2025 (ESSENCE, PMID 40305708), reported the 72-week interim analysis of Phase 3 semaglutide 2.4 mg weekly in adults with biopsy-confirmed MASH and F2/F3 fibrosis^[3]. Verified key findings:

• Resolution of steatohepatitis without worsening of fibrosis: 62.9% semaglutide vs 34.3% placebo (estimated difference 28.7 percentage points; 95% CI 21.1–36.2; P < 0.001)^[3]
• Reduction in fibrosis without worsening of steatohepatitis: 36.8% vs 22.4% (difference 14.4 pp; P < 0.001)^[3]
• Mean body-weight change: −10.5% vs −2.0% placebo^[3]

ESSENCE supported the August 2025 FDA approval of Wegovy for non-cirrhotic MASH with moderate-to-advanced fibrosis — the first GLP-1 with an FDA-approved liver indication.

Cross-trial vs tirzepatide SYNERGY-NASH Phase 2

Loomba et al., NEJM 2024 (SYNERGY-NASH, PMID 38856224), reported the 52-week Phase 2 trial of tirzepatide in 190 adults with biopsy-confirmed MASH and F2/F3 fibrosis^[4]. Verified primary endpoint:

• MASH resolution without worsening of fibrosis: 44% (5 mg) / 56% (10 mg) / 62% (15 mg) vs 10% placebo (P < 0.001 for all)^[4]

Tirzepatide has not yet received an FDA-approved MASH indication; a Phase 3 program is ongoing.

How retatrutide’s liver-fat signal sits in context

The retatrutide Phase 2a numbers are striking on the MRI-PDFF endpoint — up to 82.4% mean relative liver-fat reduction at the 12 mg dose, with 86% of participants reaching the <5% normalization threshold by 24 weeks^[1]. But MRI-PDFF reduction is not the same endpoint as the histologic MASH-resolution and fibrosis-improvement endpoints the FDA uses to approve MASH drugs. Resmetirom, semaglutide, and tirzepatide all carry biopsy-based readouts; retatrutide has only an imaging biomarker in MASLD so far. Whether the Phase 2a liver-fat signal will translate into histologic MASH resolution and fibrosis improvement in a Phase 3 trial is currently unknown.

Preclinical mechanism support

Two recent animal studies support a plausible biological rationale for retatrutide in MASH:

• Viebahn 2025 (Am J Physiol Gastrointest Liver Physiol, PMID 41056349): in an accelerated mouse model of diet-induced steatohepatitis with a fructose binge, retatrutide improved steatohepatitis histology^[5].
• Briand 2026 (Obesity, PMID 41741376): in two-species (mouse and hamster) diet-induced obese MASH models, retatrutide produced multiple metabolic benefits^[6].

These are preclinical findings. They establish biological plausibility but do not predict efficacy in humans. Reviews of the broader anti-obesity-drug landscape in MASLD (Concepción- Zavaleta 2025^[7]), GLP-1-based medications (Son 2026^[8]), glucagon-receptor pharmacology (Elmendorf 2026^[9]), and engineered multi-agonist design (Cho 2026^[10]) all flag retatrutide as a high-interest candidate but consistently note the absence of Phase 3 MASH outcome data.

What is not yet known

1. No Phase 3 retatrutide-in-MASH trial has been reported as of 2026-05-25.
2. No biopsy-confirmed histologic endpoint. The Sanyal Phase 2a used MRI-PDFF only. MASH resolution and fibrosis improvement — the endpoints the FDA has consistently required for MASH drug approval — have not been assessed for retatrutide.
3. No liver-outcome data. There is no published retatrutide data on cirrhosis development, hepatocellular carcinoma, liver transplantation, or all-cause mortality in MASH patients.
4. No head-to-head trial. There is no randomized comparison of retatrutide vs resmetirom, semaglutide, or tirzepatide in MASH.
5. Safety in MASH-specific populations. The Sanyal Phase 2a was nested in the obesity trial. Glucagon receptor agonism raises mechanistic questions specifically relevant to hepatic and glycemic safety that will need dedicated MASH-population characterization.

Practical takeaway

For a patient with biopsy-confirmed MASH and moderate-to-advanced fibrosis (F1B–F3) who wants pharmacologic treatment today, the FDA-approved options are resmetirom (Rezdiffra) — approved specifically on a MASH histologic endpoint — and semaglutide 2.4 mg (Wegovy), approved August 2025 for non-cirrhotic MASH with moderate-to-advanced fibrosis based on ESSENCE Phase 3^[3]. Tirzepatide has promising Phase 2 SYNERGY-NASH data but is not yet FDA-approved for MASH^[4].

Retatrutide is investigational and not currently prescribable for MASH. Compounded retatrutide is not a legitimate access pathway — it is not on the FDA bulk substances list, has not been through FDA review, and is in active clinical investigation. Patients interested in retatrutide for fatty liver disease should discuss enrolling in a clinical trial with a hepatologist rather than seeking compounded supply.

Patients worried about GLP-1 effects on the liver should also see our review of the question do GLP-1s cause liver damage — the trial evidence consistently shows reduced liver fat and improved liver enzymes, not harm.