PEG-MGF (Pegylated Mechano Growth Factor) is a synthetic, PEGylated form of the C-terminal peptide of mechano growth factor (MGF), a splice variant of the IGF-1 gene (IGF-1Ec in humans, IGF-1Eb in rodents). Native MGF is expressed locally in skeletal muscle immediately following mechanical overload or damage (e.g., resistance exercise). It stimulates muscle satellite cell (stem cell) activation and proliferation, initiating the early repair response before the sustained IGF-1Ea isoform takes over for differentiation. Because native MGF has an extremely short half-life (minutes), PEGylation (conjugation with polyethylene glycol) protects the peptide from enzymatic degradation, extending systemic circulation. PEG-MGF is used in the bodybuilding community for localized muscle growth. It is prohibited by WADA and not approved for human therapeutic use.
Category: Muscle & Performance. Evidence rating: D (animal/preclinical only).
Clinical status: Research-only. No human clinical trials registered or completed. Preclinical characterization primarily in cell culture and rodent models.
MGF is produced from the IGF-1 gene by alternative splicing of exons 4, 5, and 6. The unique C-terminal E domain of MGF (24 amino acids in the Ec splice variant) is responsible for its distinct biological activity compared to mature IGF-1. MGF activates muscle satellite cells (muscle stem cells)…
Research base: 30 registered clinical trials and 13 indexed publications reference PEG-MGF.
Safety considerations: No human clinical trials — safety profile is entirely unknown; No formal toxicology studies published for PEG-MGF; Theoretical oncogenic risk: satellite cell proliferation and IGF-1 pathway activation are relevant to cancer biology.
Reviewed by the PeptideAtlas Editorial Team. Last reviewed: 2026-07-05.
MGF is a splice variant of the IGF-1 gene that is expressed locally in skeletal muscle in response to mechanical loading or damage. In humans, it is the IGF-1Ec splice variant. Its unique C-terminal E domain (24 amino acids) has autonomous signaling activity distinct from mature IGF-1, specifically activating muscle satellite cells.
They target different phases of muscle growth. MGF activates and expands the satellite cell pool (proliferation phase), while IGF-1 drives differentiation of those cells into mature muscle fibers. Some bodybuilders use both sequentially. PEG-MGF acts locally; IGF-1 LR3 is systemically active.
Native MGF has an extremely short half-life (minutes) due to rapid enzymatic degradation. PEGylation attaches a polyethylene glycol chain that shields the peptide from proteases and reduces renal clearance, theoretically extending the duration of action from minutes to hours.
WADA prohibits all growth factors and their releasing factors. While specific detection methods for PEG-MGF are evolving, it falls under the S2 prohibited category and its use would constitute a doping violation.