Mechano growth factor (MGF) and PEG-MGF

Overview

Mechano growth factor (MGF) is the name for a form of IGF-1 that muscle makes after it is stretched or damaged, and for a short lab-made peptide copied from its tail end. PEG-MGF is the same idea with a chemical (PEG) attached to make it last longer. It is popular in bodybuilding circles, but it has never been tested in human clinical trials, and lab studies disagree on whether it does anything.

How it works

Proposed: the IGF-1 gene can be spliced in different ways, and one version (IGF-1Ec in humans, called MGF) rises in muscle after mechanical stress or injury. Supporters propose that its unique tail peptide activates muscle stem cells (satellite cells) to multiply before they fuse into muscle fibers, possibly acting apart from the IGF-1 receptor. This is disputed: a 2014 independent study found the native and a stabilized MGF peptide did not boost proliferation of mouse or human muscle cells or muscle stem cells, while mature IGF-1 did. Whether natural E-peptides even exist as free peptides in the body has not been confirmed.

What research shows

• Human muscle biopsy study (abstract, n=15 men): heavy one-leg exercise raised MGF mRNA after 2.5 hours in young men but not in men aged 70–82. This measured the body's own gene activity, not a drug.
• Animal and cell studies (reviewed 2012): the synthetic MGF peptide activated muscle stem cells, and in sheep, MGF given into the heart arteries after a heart attack improved heart function more than IGF-1; mouse ALS and stroke models suggested nerve protection.
• Independent cell study (2014): native and stabilized MGF peptides at up to 500 ng/ml had no effect on proliferation or differentiation of mouse or human muscle cells or mouse muscle stem cells, questioning a physiological role.
• No human clinical trials of MGF or PEG-MGF were found, and no peer-reviewed studies of PEG-MGF itself were identified.

Doses studied in people

No published human dosing data exist for MGF or PEG-MGF; doses circulating online are not based on human trials.

Read this first: these are the amounts given to participants in published studies or written on official prescribing labels, reported for reference. They are not recommendations. Trial doses were chosen for specific patients under medical supervision, and a dose that is safe in one person can be harmful in another.

Weekly protocol

How the schedule looks week by week. Each chart says where it comes from: a prescribing label, a clinical trial, or a protocol commonly reported online.

Reference only, not a recommendation. Charts marked "commonly reported" describe what public sources say people use. They have not been tested in trials, and their safety and effect are unknown. Label and trial schedules were set for specific patients under medical supervision. Use the calculator only to understand the arithmetic.

Vial math

Many research vials hold 5 or 10 mg of powder. This table shows how much ends up in each mark on a U-100 insulin syringe for common amounts of added liquid. It is arithmetic only, not a dose.

More sizes: all vial sizes · How this works: Syringes and units · Reconstitution guide.

Safety

• Unknown human safety: no clinical trials have been done.
• Products sold online are unapproved and of uncertain identity and purity; MGF has been detected in black-market anabolic products (2012 review).
• Unknown long-term safety.

Report side effects of any drug or product to the FDA through MedWatch. For a possible poisoning in the US, call Poison Control at 1-800-222-1222.

Legal status

FDA

Not FDA-approved; no approved drug contains MGF or PEG-MGF.

Compounding

"Mechano growth factor (MGF)" is in 503A Category 3 (nominated with insufficient supporting information) on FDA's list updated May 14, 2026, so it is not eligible for 503A compounding. PEG-MGF is not listed by name.

Sports (WADA)

Prohibited at all times: mechano growth factors (MGFs) are named under S2.3 (growth factors).

Other

Not a controlled substance in the US.

Rules change often. See Legal status of peptides for how these categories work.

History

MGF was described by Geoffrey Goldspink's group at University College London in the late 1990s as an IGF-1 variant made by stretched or exercised muscle. A 2002 abstract from the same group reported that heavy leg exercise raised MGF mRNA in young but not older men. Animal and cell studies in the 2000s explored muscle, heart and nerve effects of the synthetic tail peptide. A 2014 study by a team including pharmaceutical-industry researchers failed to reproduce key muscle-cell effects. MGF began appearing in black-market anabolic products, and WADA added mechano growth factors to its prohibited list.

Common questions

Related compounds

Sources

1. Zabłocka B, Goldspink PH, Goldspink G, Górecki DC. Mechano-Growth Factor: an important cog or a loose screw in the repair machinery? Front Endocrinol 2012;3:131 Journal
2. Fornaro M et al. Mechano-growth factor peptide, the COOH terminus of unprocessed IGF-1, has no apparent effect on myoblasts or primary muscle stem cells. Am J Physiol Endocrinol Metab 2014;306:E150–E156 Journal
3. Hameed M et al. Weightlifting exercise increases the mRNA expression of a mechanosensitive IGF-I (MGF) in the muscles of young, but not old men. J Physiol 2002;543P (abstract) Journal
4. Matheny RW Jr et al. Minireview: Mechano-growth factor: a putative product of IGF-I gene expression involved in tissue repair and regeneration. Endocrinology 2010 PubMed review
5. FDA: Bulk drug substances nominated for use in compounding under section 503A (updated May 14, 2026) Regulatory
6. WADA Prohibited List Regulatory