Peptide Approaches to Liver Fibrosis

Liver Fibrosis

62.9% resolution

Semaglutide 2.4 mg achieved MASH resolution without worsening fibrosis in 62.9% of patients versus 34.3% on placebo in the Phase 3 ESSENCE trial.

Sanyal et al., New England Journal of Medicine, 2025

Sanyal et al., New England Journal of Medicine, 2025

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Liver fibrosis, the progressive scarring that replaces healthy tissue with collagen deposits, was considered irreversible until recently. The liver's wound-healing machinery, driven by activated hepatic stellate cells, responds to chronic injury by laying down scar tissue that eventually chokes off normal liver function. Metabolic dysfunction-associated steatohepatitis (MASH, formerly NASH) is now the leading driver of this process globally, with metabolic dysfunction-associated steatotic liver disease (MASLD) affecting an estimated 32.4% of the world's population.^[4] Peptide-based therapeutics, particularly GLP-1 receptor agonists and dual-receptor agonists, have emerged as the most promising class for stopping and reversing this fibrotic cascade.

Why Liver Fibrosis Matters

Fibrosis is the liver's universal wound-healing response. Viral hepatitis, alcohol, and metabolic dysfunction all trigger the same pathway: hepatocyte injury activates stellate cells, which transform from quiescent vitamin A-storing cells into collagen-producing myofibroblasts. The resulting scar tissue distorts liver architecture, impairs blood flow, and ultimately progresses to cirrhosis if the underlying injury continues.

Fibrosis stage is the strongest predictor of liver-related death in MASH patients. Collagen peptide biomarkers like PRO-C3 (a marker of type III collagen formation) can track fibrosis progression non-invasively, but the gold standard for diagnosis remains liver biopsy.

Until 2024, no drug was approved specifically for MASH-related fibrosis. Resmetirom (Rezdiffra), a thyroid hormone receptor agonist, received FDA approval in March 2024, followed by semaglutide (Wegovy formulation) in August 2025. Both are non-peptide drugs, but the clinical trial landscape is dominated by peptide-based therapies that have produced some of the strongest anti-fibrotic results seen to date.

GLP-1 Receptor Agonists: The Evidence Base

GLP-1 receptor agonists reduce liver fat, inflammation, and to a lesser extent, fibrosis. Fang and colleagues conducted a systematic review and meta-analysis of 16 randomized controlled trials involving 2,178 patients treated with liraglutide, exenatide, dulaglutide, or semaglutide.^[1] The class achieved statistically significant histologic resolution of NASH with no worsening of liver fibrosis (WMD: 4.08, 95% CI 2.54-6.56), along with significant CRP reduction, indicating anti-inflammatory effects beyond weight loss.

Wang and colleagues expanded this analysis in 2025 with 25 RCTs and 2,600 patients, including newer agents like tirzepatide, survodutide, and retatrutide.^[7] GLP-1-based therapies reduced liver fat content by a mean of 5.21%, with retatrutide showing the largest effect. Histological improvements in steatosis, hepatocellular ballooning, and lobular inflammation were significant. Fibrosis improvement, while consistent in direction, did not reach statistical significance for single GLP-1 agonists alone. Tirzepatide produced more robust histological evidence than semaglutide or liraglutide.

The ESSENCE Trial: Semaglutide Phase 3

The largest and most definitive peptide trial for MASH came from the ESSENCE study, published in the New England Journal of Medicine in 2025.^[5] Sanyal and colleagues randomized 1,197 patients with biopsy-confirmed MASH and fibrosis stage F2-F3 to weekly subcutaneous semaglutide 2.4 mg or placebo for 240 weeks. The interim analysis at 72 weeks (first 800 patients) showed:

• MASH resolution without worsening fibrosis: 62.9% semaglutide vs. 34.3% placebo (difference: 28.7 percentage points, P<0.001)
• Fibrosis reduction without worsening MASH: 36.8% vs. 22.4% (difference: 14.4 percentage points, P<0.001)
• Combined resolution + fibrosis reduction: 32.7% vs. 16.1% (P<0.001)
• Body weight change: -10.5% vs. -2.0% (P<0.001)

These numbers led to FDA approval of semaglutide for MASH with F2-F3 fibrosis. The fibrosis improvement, while statistically significant, was more modest than the inflammation resolution, raising the question of whether single GLP-1 agonism is sufficient for advanced fibrotic disease.

Dual Agonists: Hitting Two Receptors for Better Fibrosis Outcomes

The rationale for dual agonism in liver disease goes beyond appetite suppression and weight loss. Glucagon receptor activation directly promotes hepatic fatty acid oxidation, meaning it attacks liver fat from a different angle than GLP-1 alone.^[4] This dual approach has produced some of the most impressive MASH trial results to date.

Tirzepatide (GIP/GLP-1 Dual Agonist)

The SYNERGY-NASH Phase 2 trial tested tirzepatide at 5, 10, and 15 mg weekly in 190 participants with MASH and F2-F3 fibrosis.^[2] MASH resolution without worsening fibrosis occurred in:

• 44% at 5 mg (vs. 10% placebo; difference: 34 percentage points)
• 56% at 10 mg (difference: 46 percentage points)
• 62% at 15 mg (difference: 53 percentage points)
• All three comparisons reached P<0.001

Fibrosis improvement by at least one stage occurred in 51-55% of tirzepatide groups versus 30% on placebo (differences of 21-25 percentage points). These fibrosis improvements are larger than those seen with semaglutide alone, suggesting the GIP receptor component may contribute additional hepatoprotective effects.

Survodutide (Glucagon/GLP-1 Dual Agonist)

Survodutide targets the glucagon and GLP-1 receptors, a different combination than tirzepatide. In a Phase 2 trial of 293 adults with MASH and F1-F3 fibrosis, MASH improvement without fibrosis worsening occurred in:^[3]

• 47% at 2.4 mg
• 62% at 4.8 mg
• 43% at 6.0 mg
• 14% on placebo (P<0.001 for dose-response)

Liver fat decreased by at least 30% in 57-67% of survodutide groups versus 14% on placebo. Fibrosis improved by at least one stage in 34-36% versus 22%. The inverted dose-response at the highest dose (6.0 mg performing worse than 4.8 mg) likely reflects tolerability issues: nausea occurred in 66% of survodutide patients versus 23% on placebo, with vomiting in 41% versus 4%.

The glucagon receptor component may be particularly relevant for liver disease because glucagon directly drives hepatic lipid oxidation. Retatrutide, which adds GIP activation to the GLP-1/glucagon combination, has shown even larger liver fat reductions in early trials.

How Peptide Therapies Compare: The Network Meta-Analysis

Souza and colleagues published the most comprehensive comparison of MASH therapies in 2025, analyzing 29 randomized controlled trials with 9,324 patients using network meta-analysis.^[6]

For MASH resolution without worsening fibrosis, the top-ranked agents by SUCRA (surface under the cumulative ranking curve) were:

1. Pegozafermin (FGF21 analog): SUCRA 91.75
2. Survodutide: SUCRA 90.87
3. Tirzepatide: SUCRA 84.70

For fibrosis regression without worsening MASH, the rankings shifted:

1. Pegozafermin: SUCRA 79.92
2. Cilofexor + firsocostat (FXR/ACC combination): SUCRA 71.38
3. Cilofexor + selonsertib: SUCRA 69.11

Eight agents outperformed placebo for fibrosis regression with statistical significance. Twelve did so for MASH resolution. Peptide-based drugs (tirzepatide, semaglutide, survodutide, liraglutide) appeared consistently across both rankings, though they performed better for MASH resolution than for fibrosis regression specifically.

Peptide-Based Approaches Beyond GLP-1

Several non-GLP-1 peptide strategies target liver fibrosis through distinct mechanisms:

Pemvidutide (GLP-1/glucagon dual agonist, Altimmune) showed MASH resolution without fibrosis worsening in 58% at 1.2 mg versus 20% on placebo in the Phase 2 IMPACT trial, though fibrosis improvement did not reach statistical significance.

Pegozafermin (FGF21 analog) ranked first in the network meta-analysis for both fibrosis regression and MASH resolution. FGF21 analogs work through a fundamentally different mechanism than GLP-1 drugs: they directly reduce hepatic lipogenesis, enhance fatty acid oxidation, and reduce stellate cell activation. This non-incretin approach may explain their superior ranking for fibrosis specifically.

Efruxifermin (another FGF21 analog) has also shown significant MASH and fibrosis improvement in Phase 2 trials, ranking among the top agents in the network meta-analysis.

These results suggest that the most effective future regimens may combine peptide classes: a GLP-1-based agonist for metabolic improvement with an FGF21 analog for direct anti-fibrotic activity.

What Remains Unresolved

Single GLP-1 agonists may not be enough for advanced fibrosis. While semaglutide achieved significant fibrosis improvement in the ESSENCE trial, the effect size was modest (36.8% vs. 22.4%). In a separate trial of MASH-related compensated cirrhosis, semaglutide did not achieve MASH resolution or fibrosis improvement versus placebo.^[7] This suggests a ceiling to what GLP-1 agonism alone can achieve in the most advanced disease.

Weight loss may not fully explain liver benefit. Patients in these trials lose substantial weight (8-15% body weight), and disentangling the liver-specific effects of these peptides from their weight-loss effects remains difficult. Some evidence suggests direct hepatic mechanisms: GLP-1 receptors are expressed on hepatocytes, and glucagon receptor activation drives hepatic fat oxidation independently of calorie reduction.

Long-term durability is unknown. Most trials report 48-72 week results. Whether fibrosis improvement persists, progresses further, or reverses after treatment discontinuation has not been established. The ESSENCE trial will run 240 weeks total, which should provide the first long-term dataset.

Gastrointestinal tolerability limits dose optimization. Nausea, diarrhea, and vomiting are common across all GLP-1-based therapies. The survodutide trial showed that the highest dose (6.0 mg) performed worse than the middle dose (4.8 mg), likely because tolerability-driven dropouts reduced the evaluable population.

Head-to-head comparisons between peptide classes are absent. The network meta-analysis provides indirect comparisons, but no trial has directly compared semaglutide vs. tirzepatide vs. survodutide for liver endpoints. Such trials would clarify whether dual agonism provides meaningful fibrosis advantages over single GLP-1 therapy.

The Bottom Line

Peptide-based therapeutics have transformed the liver fibrosis treatment landscape. GLP-1 agonists like semaglutide resolve MASH inflammation effectively, while dual agonists like tirzepatide and survodutide show larger fibrosis improvements. A 2025 network meta-analysis of 29 trials ranked survodutide and tirzepatide among the top three agents for MASH resolution. The field is moving toward multi-receptor agonism and combination regimens, with the recognition that fibrosis reversal likely requires direct hepatic mechanisms beyond weight loss.

Frequently Asked Questions

Can GLP-1 drugs reverse liver fibrosis?

GLP-1 receptor agonists can improve liver fibrosis, though the effect is modest with single-agonist therapy. In the ESSENCE Phase 3 trial, semaglutide 2.4 mg improved fibrosis by at least one stage in 36.8% of patients versus 22.4% on placebo (Sanyal et al., 2025). Dual agonists like tirzepatide and survodutide show larger fibrosis improvements, with tirzepatide achieving 51-55% fibrosis improvement versus 30% on placebo (Loomba et al., 2024).

What is the best drug for MASH liver disease?

A 2025 network meta-analysis of 29 clinical trials with 9,324 patients ranked pegozafermin (an FGF21 analog) first for both MASH resolution and fibrosis improvement, followed by survodutide and tirzepatide (Souza et al., 2025). Semaglutide and resmetirom are currently the only FDA-approved drugs for MASH. The best choice depends on individual patient factors including fibrosis stage and metabolic comorbidities.

How does tirzepatide help the liver?

Tirzepatide activates both GIP and GLP-1 receptors, reducing liver fat, inflammation, and fibrosis. In the SYNERGY-NASH trial, 62% of patients on tirzepatide 15 mg achieved MASH resolution versus 10% on placebo after 52 weeks (Loomba et al., 2024, NEJM). The dual mechanism may provide liver benefits beyond what single GLP-1 agonists achieve, with 51-55% of patients showing fibrosis improvement versus 30% on placebo.

What is survodutide and how does it treat fatty liver?

Survodutide is a dual glucagon/GLP-1 receptor agonist that treats fatty liver disease by combining GLP-1's metabolic benefits with glucagon's ability to directly promote fat burning in liver cells. In a Phase 2 NEJM trial, survodutide achieved MASH improvement in up to 62% of patients versus 14% on placebo, with 57-67% achieving at least 30% liver fat reduction (Sanyal et al., 2024).

Is liver fibrosis reversible?

Yes, liver fibrosis can be reversed, though the degree depends on the cause and stage. In clinical trials of peptide-based drugs, 34-55% of patients with MASH and moderate-to-severe fibrosis showed fibrosis improvement by at least one stage after 48-72 weeks of treatment. Fibrosis regression is most achievable in stages F1-F3; established cirrhosis (F4) appears more resistant, with semaglutide failing to improve fibrosis in one cirrhosis trial.

What causes liver fibrosis in MASH?

In MASH, chronic metabolic injury from excess liver fat triggers inflammation, which activates hepatic stellate cells. These cells transform into collagen-producing myofibroblasts that deposit scar tissue throughout the liver. The fibrotic process distorts liver architecture, impairs blood flow, and can progress to cirrhosis if the underlying metabolic injury continues. MASLD, the precursor to MASH, affects approximately 32.4% of the global population (Singh et al., 2024).