MASH/NASH Peptide Therapeutics: Resmetirom, Semaglutide, Tirzepatide, and Pipeline Analysis 2026

Industry Authority | 2026-07-10 | 12 min read

A 2026 industry review of MASH/NASH peptide therapeutics: resmetirom mechanism, semaglutide/tirzepatide/survodutide MASH trials, FGF21 analogs, and the evolving treatment landscape.

Introduction: MASH as a major unmet need

MASH (Metabolic dysfunction-Associated Steatohepatitis, formerly NASH) is a progressive liver disease that represents the leading cause of liver transplantation in the United States. The disease affects approximately 5-6% of adults globally and is strongly associated with obesity, type 2 diabetes, and metabolic syndrome.

The natural history of MASH follows a progression: simple steatosis (fatty liver) → MASH (steatosis with inflammation and hepatocyte injury) → fibrosis (F1-F4 stages) → cirrhosis (F4) → hepatocellular carcinoma. Fibrosis stage is the strongest predictor of liver-related mortality and transplantation need.

Until 2024, no pharmacological therapies were approved for MASH. The treatment landscape has transformed with resmetirom approval and multiple GLP-1-based therapies showing promise in Phase 3 trials.

MASH pathophysiology

MASH results from multiple parallel insults to the liver:

Lipotoxicity

Excess free fatty acids in hepatocytes lead to:

  • Ceramide accumulation (toxic lipid metabolite)
  • Diacylglycerol accumulation
  • Mitochondrial dysfunction
  • ER stress

Insulin resistance

Systemic insulin resistance promotes:

  • Increased hepatic de novo lipogenesis
  • Reduced fatty acid oxidation
  • Increased VLDL production
  • Hepatic steatosis

Inflammation

Inflammatory pathways activated in MASH include:

  • NF-κB signaling
  • JNK activation
  • Kupffer cell activation
  • NASH-associated macrophages (NAMs)

Gut-liver axis

Gut dysbiosis and increased intestinal permeability ("leaky gut") contribute to:

  • Portal endotoxin delivery
  • Kupffer cell activation
  • hepatic inflammation

GLP-1 agonists in MASH

Semaglutide in MASH (ESSENCE trial)

The ESSENCE Phase 3 trial evaluated semaglutide 2.4 mg weekly in MASH with F2-F3 fibrosis:

  • MASH resolution: 62.8% (vs. 34.3% placebo)
  • Fibrosis improvement ≥1 stage: 34.3% (vs. 22.5% placebo)
  • Liver fat reduction: 35-50% by MRI-PDFF
  • Significant HbA1c and weight reduction

Semaglutide is positioned as a leading MASH therapy, with regulatory submission expected in 2026.

Tirzepatide in MASH (SYNERGY-NASH)

The SYNERGY-NASH Phase 3 trial evaluated tirzepatide (GLP-1/GIP dual agonist) in MASH:

  • MASH resolution: 51-62% across doses (vs. 11% placebo)
  • Fibrosis improvement: 24-30% (vs. 13% placebo)
  • Liver fat reduction: 35-45% by MRI-PDFF
  • Greater weight loss than semaglutide (18-22% vs. 12-15%)

The dual mechanism may provide additional MASH benefit through:

  • Greater weight loss
  • Improved insulin sensitivity
  • Reduced hepatic de novo lipogenesis

Survodutide in MASH

Boehringer Ingelheim's survodutide (GLP-1/glucagon dual agonist) is in Phase 3 LIVERAGE trials. The glucagon component is particularly relevant for MASH because it:

  • Increases hepatic fatty acid oxidation
  • Reduces hepatic steatosis directly
  • Improves mitochondrial function
  • May increase energy expenditure

Resmetirom: the first MASH approval

Resmetirom (Rezdiffra) was FDA-approved in March 2024 as the first MASH therapy.

Mechanism

Resmetirom is a selective thyroid hormone receptor beta (THR-β) agonist. THR-β is the predominant THR isoform in liver (vs. THR-α in heart).

THR-β activation in liver:

  • Increases hepatic fatty acid oxidation
  • Increases mitochondrial biogenesis
  • Reduces de novo lipogenesis
  • Lowers LDL cholesterol

THR-β selectivity avoids the cardiac effects of THR-α activation (tachycardia, arrhythmias).

MAESTRO-NASH trial results

  • MASH resolution: 25.9% (80 mg) and 29.9% (100 mg) vs. 9.7% placebo
  • Fibrosis improvement ≥1 stage: 24.2% (80 mg) and 25.9% (100 mg) vs. 14.2% placebo
  • LDL cholesterol reduction: 13-16%
  • Liver fat reduction: 30-37%

Limitations of resmetirom

Resmetirom achieves significant MASH improvement but:

  • No weight loss (unlike GLP-1 agonists)
  • Modest absolute effect size
  • Does not address metabolic comorbidities

Combination therapy (resmetirom + GLP-1 agonist) is being explored.

FGF21 analogs

FGF21 is a hepatokine with beneficial metabolic effects:

  • Increased fatty acid oxidation
  • Improved insulin sensitivity
  • Reduced hepatic gluconeogenesis
  • Anti-inflammatory effects

Efruxifermin (EFX)

Akero Therapeutics' efruxifermin is an Fc-fusion FGF21 analog:

  • Long half-life (3-4 days)
  • Phase 2b HARMONY trial in MASH
  • Significant fibrosis improvement at 24 weeks
  • Phase 3 trials ongoing

HARMONY results:

  • MASH resolution: 50-70%
  • Fibrosis improvement: 30-40%
  • Liver fat reduction: 50-65%

Pegozafermin

Bio89min Therapeutics' pegozafermin is a glycoPEGylated FGF21:

  • Extended half-life via PEGylation
  • Phase 2b HENIX trial
  • Significant MASH and fibrosis improvement
  • Phase 3 trials planned

Summary

MASH/NASH is a major unmet need with several therapeutic classes now in clinical development. Resmetirom has set a regulatory precedent as the first MASH approval. Peptide therapies (GLP-1 RA, dual agonists, FGF21 analogs) achieve strong MASH resolution with the additional benefit of weight loss (for GLP-1-based therapies). Combination strategies may provide the best outcomes.

ZePeptide content is for lawful laboratory and in-vitro research sourcing. Products are not supplied for human or veterinary use.

Research peptide catalogSupplier checklistMore peptide guides