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    Efruxifermin

    Low Evidence

    Efruxifermin (development codes EFX, AKR-001; originally AMG 876) is an investigational, once-weekly, subcutaneously injected analog of the metabolic hormone fibroblast growth factor 21 (FGF21) being developed by Akero Therapeutics for metabolic dysfunction-associated steatohepatitis (MASH, formerly NASH), including both pre-cirrhotic fibrosis and compensated (F4) cirrhosis. It is a bivalent Fc-FGF21 fusion protein - two engineered FGF21 sequences fused to a human immunoglobulin (IgG1) Fc domain - a design distinct from the glycoPEGylation used by its main FGF21-class rival, pegozafermin. The Fc fusion extends the very short half-life of native FGF21 to support once-weekly dosing while preserving agonism at FGF receptors (FGFR1c/2c/3c) together with the co-receptor beta-Klotho. In the 96-week Phase 2b HARMONY trial in biopsy-confirmed F2-F3 MASH, at least a one-stage improvement in fibrosis without worsening of MASH was reached by about 75% of patients on 50 mg and 46% on 28 mg versus 24% on placebo (published in The Lancet, August 2025). In the Phase 2b SYMMETRY trial in compensated MASH cirrhosis, about 39% of 50 mg patients with paired week-96 biopsies achieved reversal of cirrhosis without worsening of MASH versus 15% on placebo (published in the New England Journal of Medicine). Efruxifermin holds FDA Breakthrough Therapy designation and has advanced into the Phase 3 SYNCHRONY program (SYNCHRONY Histology in F2-F3 MASH, SYNCHRONY Outcomes in F4 compensated cirrhosis, and SYNCHRONY Real-World in non-invasively diagnosed MASH/MASLD, whose double-blind portion completed enrollment with safety results expected in 2026).

    AliasesEfruxifermin+6 more
    EvidenceLow Evidence
    Last Updated 2026-07-13
    Reading Time 6 min

    What It Is

    Efruxifermin (EFX) is an investigational, once-weekly, subcutaneously injected analog of fibroblast growth factor 21 (FGF21), the endogenous hormone that helps the body respond to metabolic stress. Native FGF21 is secreted mainly by the liver and acts through FGF receptors and the co-receptor beta-Klotho in liver, adipose tissue, and the central nervous system to improve insulin sensitivity, increase fat oxidation, lower circulating triglycerides, and reduce hepatic fat, inflammation, and fibrosis - but it is cleared from the body within hours, making it impractical as a drug. Efruxifermin is engineered to overcome this: it is a bivalent Fc-FGF21 fusion protein in which two modified FGF21 sequences are fused to a human IgG1 Fc domain, an approach that both stabilizes the molecule and slows its clearance enough to allow once-weekly injection, while a set of point mutations preserves potent receptor activity. This Fc-fusion strategy is the key structural contrast with pegozafermin, the other leading FGF21 analog, which instead uses site-specific glycoPEGylation. Developed by Akero Therapeutics (the molecule originated at Amgen as AMG 876), efruxifermin has become one of the most advanced FGF21-pathway therapies and a central test of whether directly engaging FGF21 can not only cut liver fat but actually reverse fibrosis - and even established cirrhosis - in MASH. Its clinical program spans the full fibrosis spectrum, from pre-cirrhotic F2-F3 disease (BALANCED, HARMONY, and Phase 3 SYNCHRONY Histology) to compensated F4 cirrhosis (SYMMETRY and Phase 3 SYNCHRONY Outcomes), plus a large real-world safety study, SYNCHRONY Real-World.

    Also known as: Efruxifermin, EFX, AKR-001, AMG 876, Fc-FGF21 fusion protein, Akero FGF21 analog, efruxifermin (MASH)

    Regulatory Status

    Why Researchers Study It

    Efruxifermin is one of the two most advanced FGF21 analogs and, alongside pegozafermin, a decisive test of whether directly engaging the FGF21 metabolic pathway can reverse liver fibrosis - and even compensated cirrhosis - in MASH, the outcomes regulators care about most. Because it works through a mechanism entirely different from the GLP-1/GIP/glucagon incretin drugs, it is studied both as a standalone MASH therapy across the full fibrosis spectrum and as a potential future combination partner for incretin-based weight-loss agents. Its Fc-FGF21 fusion design versus pegozafermin's glycoPEGylation makes the two a closely watched head-to-head on how best to drug the FGF21 pathway, and Akero's Phase 3 SYNCHRONY readouts are viewed as a bellwether for the entire MASH field.

    Proposed Mechanisms

    • FGF21 receptor agonism: efruxifermin activates FGF receptor complexes (FGFR1c, FGFR2c, and FGFR3c) together with the co-receptor beta-Klotho in liver, adipose tissue, and other metabolic tissues, reproducing and amplifying the actions of native FGF21.
    • Direct hepatic effects: reduces hepatic de novo lipogenesis and liver fat, and drives anti-inflammatory and anti-fibrotic actions in the liver, aiming to reverse steatohepatitis and, in advanced disease, established fibrosis and cirrhosis.
    • Improved insulin sensitivity and lipid handling: enhances peripheral glucose uptake and fat oxidation and lowers circulating triglycerides while improving the cholesterol profile, targeting the metabolic drivers of MASH.
    • Adipose-tissue signaling: acts on fat to raise adiponectin and promote healthier lipid storage, part of the broader FGF21 metabolic program.
    • Fc-fusion half-life extension: fusing two FGF21 sequences to a human IgG1 Fc domain stabilizes the protein and slows clearance enough to allow once-weekly subcutaneous dosing while preserving receptor potency - a structural contrast with pegozafermin's glycoPEGylation approach.

    Evidence Snapshot

    Low Evidence
    Low
    Medium
    High
    Study Type Model Outcome Link
    RCT (human, Phase 2b - HARMONY, 96 weeks) Biopsy-confirmed F2-F3 (pre-cirrhotic) MASH; once-weekly subcutaneous efruxifermin 28 mg or 50 mg vs placebo across 41 US centers At least one-stage fibrosis improvement without worsening of MASH at week 96 in ~75% (50 mg) and ~46% (28 mg) vs ~24% placebo; near-complete disease reversal in roughly one-third of the 50 mg group, with improvements in liver injury and metabolic markers Source
    RCT (human, Phase 2b - SYMMETRY, 96 weeks) Compensated (F4) cirrhosis due to MASH; once-weekly subcutaneous efruxifermin 28 mg or 50 mg vs placebo Reversal of cirrhosis (>=1-stage fibrosis improvement to F3 or better) without worsening of MASH at week 96 in ~39% of 50 mg patients with paired biopsies vs ~15% placebo (p=0.009); ~29% in the intent-to-treat analysis counting missing biopsies as failures Source
    RCT (human, Phase 3 - SYNCHRONY program, ongoing) SYNCHRONY Histology (F2-F3 MASH), SYNCHRONY Outcomes (compensated F4 cirrhosis, initiated June 2024), and SYNCHRONY Real-World (non-invasively diagnosed MASH/MASLD, F1-F4, ~601 patients; once-weekly 50 mg vs placebo) Pivotal program designed to confirm fibrosis improvement, MASH resolution, cirrhosis reversal, and clinical outcomes; SYNCHRONY Real-World completed double-blind enrollment with safety/tolerability results expected in 2026 Source

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    Safety & Cautions

    • Investigational and not approved: efruxifermin is in Phase 3 development for MASH across the fibrosis spectrum and is not available by prescription; its ability to improve fibrosis and clinical outcomes in the pivotal Phase 3 SYNCHRONY trials remains to be confirmed.
    • No self-sourcing: efruxifermin is a proprietary, engineered Fc-FGF21 fusion biologic studied only in controlled trials. Material sold online as 'efruxifermin', 'EFX', 'AKR-001', or 'FGF21' is not the clinical drug and cannot be assumed authentic, pure, or safe.
    • Gastrointestinal effects and appetite: the most commonly reported adverse effects in trials are diarrhea, nausea, and increased appetite, generally mild-to-moderate and transient.
    • FGF21-class considerations: agents in this class have been examined for possible effects on bone-turnover markers and other parameters; the long-term significance of these signals is still being studied.
    • Not a weight-loss or obesity drug: unlike the incretins, efruxifermin is being developed for liver disease (MASH), and it should not be conflated with GLP-1/GIP-based weight-loss therapies.

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    Citations

    1. [1] Safety and efficacy of once-weekly efruxifermin versus placebo in MASH (HARMONY): 96-week results from a Phase 2b trial - The Lancet (August 2025) PubMed
    2. [2] Efruxifermin in Compensated Liver Cirrhosis Caused by MASH (SYMMETRY) - New England Journal of Medicine PubMed
    3. [3] Akero Therapeutics Announces Initiation of Phase 3 SYNCHRONY Outcomes Trial of Efruxifermin in Patients with Compensated Cirrhosis (F4) Due to MASH PubMed
    4. [4] Akero Therapeutics Completes Enrollment of the Double-Blind Portion of the Phase 3 SYNCHRONY Real-World Study - Akero Therapeutics PubMed
    5. [5] Efruxifermin for MASH - Akero Therapeutics (mechanism and clinical program overview) PubMed

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