Efruxifermin: A Literature Course in Six Modules

This course collects what the peer-reviewed literature says about efruxifermin, an investigational engineered analogue of fibroblast growth factor 21 (FGF21). Each module summarises published study design, reported findings and adverse events, then closes with the limits of that evidence. This page is for educational purposes only and is not medical advice; consult a licensed physician about any medical question, medication or laboratory test. Nothing here is a protocol, a recommendation or a suggestion that any reader use this compound.

Module 1 — What Efruxifermin Is and How It Has Been Studied

Efruxifermin is described in the literature as a long-acting bivalent Fc–FGF21 fusion protein, meaning two modified FGF21 sequences are fused to an immunoglobulin Fc fragment to slow clearance and extend exposure relative to native FGF21, which the review literature characterises as short-lived (PMID 37376813). It is therefore classed as a biologic protein therapeutic rather than a small molecule, and it is not a naturally occurring human peptide sold as such; it is an engineered construct developed and evaluated as an investigational drug candidate (PMID 37376813).

Across the clinical programme, researchers administered efruxifermin as a subcutaneous injection once weekly: a phase 2a trial in non-alcoholic steatohepatitis (NASH) evaluated 28 mg, 50 mg and 70 mg once weekly for 16 weeks (PMID 34239138), while the phase 2b HARMONY trial in metabolic dysfunction-associated steatohepatitis (MASH) with fibrosis evaluated 28 mg and 50 mg once weekly against placebo (PMID 37802088). A separate phase 2a study administered once-weekly efruxifermin to patients with compensated NASH cirrhosis over 16 weeks (PMID 36644237), and a randomised phase 2b trial reported in 2025 studied 28 mg and 50 mg once weekly in adults with compensated cirrhosis caused by MASH (PMID 40341827).

Preclinical work is also part of the record. A rat study characterised the same long-acting Fc-fusion FGF21 analogue and reported that it reduced body-weight gain in Sprague Dawley rats without increasing sympathetic tone or urine volume (PMID 34773249).

Published study map

Limits of Module 1: every clinical study identified here is phase 2; the published record contains no phase 3 outcome trial, and the populations studied were selected trial participants with biopsy-characterised liver disease rather than the general public (PMID 37376813, PMID 40937291).

Module 2 — Mechanism as Described in the Literature

The review literature describes efruxifermin as an FGF21 analogue designed to engage the FGF21 receptor complex — FGF receptors paired with the co-receptor β-Klotho — in adipose tissue, liver and other metabolically active tissues, with downstream effects on lipid handling, insulin sensitivity and hepatic stellate-cell driven fibrogenesis proposed as the rationale for testing it in fibrotic and cirrhotic NASH (PMID 37376813). Investigators framed the phase 2a trial around that rationale by measuring hepatic fat fraction alongside markers of lipid and glucose metabolism (PMID 34239138).

Because native FGF21 has a very short circulating life, the Fc-fusion format is the mechanistic feature that the literature links to once-weekly subcutaneous administration in trials (PMID 37376813, PMID 34239138). Preclinical pharmacology addressed a class-level question about FGF21 analogues — whether metabolic effects come at the cost of sympathetic activation — and the rat study reported reduced body-weight gain without increased sympathetic tone or urine volume (PMID 34773249).

Limits of Module 2: mechanism in these papers is largely inferred from receptor biology and from biomarker movement in trial participants; none of the cited clinical reports demonstrates a receptor-level mechanism directly in humans, and rodent findings do not establish human physiology (PMID 34773249, PMID 37376813).

Module 3 — Reported Outcomes by Study

Phase 2a in NASH

In the randomised, double-blind, placebo-controlled phase 2a trial, researchers assessed once-weekly efruxifermin at 28, 50 and 70 mg over 16 weeks and reported change in hepatic fat fraction measured by MRI-PDFF as the primary endpoint, with greater reductions in the efruxifermin groups than in the placebo group (PMID 34239138). The study also reported changes in liver injury and lipid markers among treated participants (PMID 34239138).

Phase 2b HARMONY at 24 and 96 weeks

HARMONY randomised participants with MASH and fibrosis to 28 mg, 50 mg or placebo once weekly, and at 24 weeks the study reported a higher proportion of participants meeting the histological endpoint of at least one-stage fibrosis improvement without worsening of steatohepatitis in the efruxifermin groups than in the placebo group (PMID 37802088). The 96-week report from the same randomised cohort extended histological and safety follow-up for both dose groups versus placebo (PMID 40818852).

Cirrhosis studies

The phase 2a trial in compensated NASH cirrhosis was designed primarily around safety and tolerability over 16 weeks of once-weekly dosing, with exploratory non-invasive and biomarker measures reported (PMID 36644237). The larger randomised trial in compensated cirrhosis caused by MASH compared 28 mg and 50 mg once weekly with placebo and reported fibrosis-stage and safety outcomes in that more advanced population (PMID 40341827).

Combination with a GLP-1 receptor agonist

A randomised phase 2 study added once-weekly efruxifermin to stable GLP-1 receptor agonist therapy in patients with NASH/MASH and type 2 diabetes and reported safety and efficacy measures, including liver fat and metabolic parameters, for the combination (PMID 38447814).

Pooled analyses

A systematic review and meta-analysis pooled randomised data and reported that efruxifermin was associated with improvement in liver fibrosis endpoints compared with placebo in NASH/MASH populations (PMID 40520164). An updated systematic review and meta-analysis reported pooled efficacy and safety estimates across the available trials (PMID 42007332), and a network meta-analysis compared efruxifermin with resmetirom for MASH using indirect comparison of randomised trials (PMID 41947319). A further systematic review summarised safety and efficacy across the MASH programme (PMID 40937291).

Limits of Module 3: these are trial-level surrogate and histological endpoints over weeks to months, not demonstrations that liver-related death, transplantation or decompensation were prevented; pooled analyses inherit the small sample sizes, short durations and heterogeneity of the phase 2 trials they combine, and indirect comparisons are not head-to-head trials (PMID 40520164, PMID 41947319, PMID 42007332). No outcome above should be read as a promise of benefit for any individual.

Module 4 — Efruxifermin Side Effects: What Studies Report

Adverse events in this programme were reported most consistently as gastrointestinal and generally mild to moderate in severity. The phase 2a NASH trial reported that the most common adverse events among participants receiving efruxifermin were gastrointestinal, including diarrhoea, nausea and increased appetite, mostly graded mild or moderate (PMID 34239138). The phase 2b HARMONY 24-week report similarly described diarrhoea, nausea and increased appetite as the most frequent treatment-emergent events, occurring more often with efruxifermin 28 mg and 50 mg than with placebo (PMID 37802088), and the 96-week report extended safety reporting over longer exposure in the same cohort (PMID 40818852).

• Gastrointestinal events: diarrhoea, nausea and increased appetite were the events reported most often with efruxifermin in both the phase 2a and phase 2b trials (PMID 34239138, PMID 37802088).
• Tolerability in cirrhosis: the phase 2a cirrhosis trial was designed around safety and tolerability of once-weekly dosing and reported the adverse-event profile in that population (PMID 36644237), as did the later randomised trial in compensated cirrhosis caused by MASH (PMID 40341827).
• With a GLP-1 receptor agonist: the randomised add-on study reported safety alongside efficacy when efruxifermin was combined with a GLP-1 receptor agonist in patients with MASH and type 2 diabetes (PMID 38447814).
• Pooled safety: systematic reviews and meta-analyses reported pooled adverse-event and discontinuation data across trials, with gastrointestinal events again the dominant category (PMID 42007332, PMID 40937291), and a network meta-analysis reported comparative safety against resmetirom (PMID 41947319).

Limits of Module 4: adverse-event data come from a few hundred monitored trial participants followed for up to about two years, so uncommon or delayed harms could not be detected; trials excluded many comorbidities and concomitant medications, and no cited paper characterises safety in pregnancy, adolescence, or unsupervised non-trial use (PMID 40937291, PMID 40818852).

Module 5 — Pharmacokinetics Where Data Exist

Explicit human pharmacokinetic parameters are sparse in the cited literature. What the record supports is structural: the Fc-fusion design is described as producing a long-acting molecule, and every clinical trial cited here used once-weekly subcutaneous administration, consistent with an extended exposure profile (PMID 37376813, PMID 34239138). Dose levels carried forward across the programme narrowed from 28, 50 and 70 mg weekly in phase 2a (PMID 34239138) to 28 mg and 50 mg weekly in the phase 2b trials (PMID 37802088, PMID 40341827).

Preclinical pharmacology in rats reported effects on body-weight gain with the long-acting Fc-FGF21 analogue and specifically assessed sympathetic tone and urine volume, neither of which increased in that model (PMID 34773249).

Limits of Module 5: the abstracts cited here do not provide half-life, clearance, volume of distribution, bioavailability, immunogenicity or hepatic-impairment adjustment figures, and none of them addresses oral, intranasal or topical delivery; any numeric pharmacokinetic claim beyond the once-weekly schedule used in trials would go beyond the verified record (PMID 37376813, PMID 34239138).

Module 6 — Regulatory Status, Stated Factually

Efruxifermin is described throughout the cited literature as an investigational treatment for fibrotic or cirrhotic steatohepatitis, evaluated in randomised phase 2 trials (PMID 37376813, PMID 40818852). None of the cited papers describes an approved efruxifermin product, an approved label, or an authorised indication in any jurisdiction; the comparator discussed in the network meta-analysis literature for MASH is resmetirom, which that analysis treats as the approved-drug reference point (PMID 41947319).

In practical regulatory terms, an investigational biologic without marketing approval is available only through clinical trials or regulated expanded-access pathways; material offered outside those channels is typically labelled "research use only" and is not authorised for human administration. Compounding pathways in the United States apply to substances that appear on the relevant FDA bulk-substances lists or are components of approved drugs, and the cited literature does not describe efruxifermin as an approved product or an established compounding substance (PMID 37376813). Regulatory status can change and varies by country. This section is general information, not legal advice.

Limits of Module 6: the verified papers are clinical and review publications, not regulatory documents, so they establish investigational status and trial context but not current agency decisions, scheduling, import rules or pharmacy law in any specific jurisdiction (PMID 37376813, PMID 40341827).

What the Studies Did Not Test

Readers finishing this course should be as clear about the gaps as about the findings. Within the verified literature:

1. No phase 3 outcome data. The cited randomised trials were phase 2a and 2b, with histological and biomarker endpoints rather than long-term clinical outcomes (PMID 37802088, PMID 40341827).
2. No healthy-population studies. Participants had biopsy- or imaging-characterised NASH/MASH or compensated cirrhosis, so nothing in these papers describes effects in people without liver disease (PMID 34239138, PMID 36644237).
3. No weight-loss or body-composition indication. Body-weight effects in the verified record come from a rat study of the Fc-FGF21 analogue, not from a human weight-management trial (PMID 34773249).
4. No multi-year safety surveillance. The longest cited exposure is the 96-week phase 2b follow-up, and pooled reviews note the limited size and duration of the evidence base (PMID 40818852, PMID 40937291).
5. No head-to-head trial against approved MASH therapy. Comparison with resmetirom in the literature is indirect via network meta-analysis (PMID 41947319).
6. No combination testing beyond the studied GLP-1 receptor agonist add-on setting in the cited papers (PMID 38447814).

Again: this page is for educational purposes only and is not medical advice; consult a licensed physician about any decision involving investigational drugs, liver disease or laboratory monitoring.

References

• Efruxifermin in non-alcoholic steatohepatitis: a randomized, double-blind, placebo-controlled, phase 2a trial (Nature Medicine, 2021)
• Efruxifermin, a long-acting Fc-fusion FGF21 analogue, reduces body weight gain but does not increase sympathetic tone or urine volume in Sprague Dawley rats (British Journal of Pharmacology, 2022)
• A randomized, double-blind, placebo-controlled phase IIa trial of efruxifermin for patients with compensated NASH cirrhosis (JHEP Reports, 2023)
• Efruxifermin, an investigational treatment for fibrotic or cirrhotic nonalcoholic steatohepatitis (NASH) (Expert Opinion on Investigational Drugs, 2023)
• Safety and efficacy of once-weekly efruxifermin versus placebo in non-alcoholic steatohepatitis (HARMONY): a multicentre, randomised, double-blind, placebo-controlled, phase 2b trial (The Lancet Gastroenterology & Hepatology, 2023)
• Safety and Efficacy of Efruxifermin in Combination With a GLP-1 Receptor Agonist in Patients With NASH/MASH and Type 2 Diabetes in a Randomized Phase 2 Study (Clinical Gastroenterology and Hepatology, 2025)
• Efruxifermin in Compensated Liver Cirrhosis Caused by MASH (New England Journal of Medicine, 2025)
• A systematic review and meta-analysis of efruxifermin's efficacy in improving liver fibrosis in patients with NASH/MASH (Frontiers in Pharmacology, 2025)
• Safety and efficacy of once-weekly efruxifermin versus placebo in metabolic dysfunction-associated steatohepatitis (HARMONY): 96-week results from a multicentre, randomised, double-blind, placebo-controlled, phase 2b trial (The Lancet, 2025)
• Safety and efficacy of efruxifermin in metabolic dysfunction-associated steatohepatitis: A systematic review (World Journal of Gastrointestinal Pharmacology and Therapeutics, 2025)
• Efficacy and safety of efruxifermin for patients with NASH/MASH: an updated systematic review and meta-analysis (Frontiers in Pharmacology, 2025)
• Comparative Efficacy and Safety of Resmetirom and Efruxifermin for Metabolic Dysfunction-Associated Steatohepatitis: A Network Meta-Analysis of Randomized Controlled Trials (Endocrinology, Diabetes & Metabolism, 2026)