Peptides for muscle growth: what the research shows

  • 6 compounds
  • Evidence level on each
  • Last reviewed Nov 3, 2026

What they are

“Peptides for muscle growth” covers two kinds of compound. Growth hormone peptides raise the body’s own growth hormone. The compounds on this page act closer to the muscle: IGF-1 LR3, IGF-1 DES and MGF are forms of the growth signal muscle responds to, and follistatin and ACE-031 block myostatin. None is FDA-approved, and only two have been studied in people.

This page covers compounds studied for building muscle directly: IGF-1 variants, mechano growth factor (MGF), and blockers of myostatin, the body’s brake on muscle size. Compounds that raise growth hormone, such as the peptides CJC-1295 and ipamorelin and the non-peptide MK-677, are on our growth hormone page. Here is what each one is, what it has been studied in, and what the studies found.

The compounds

IGF-1 LR3

A lab-made, longer form of IGF-1, the hormone that carries much of growth hormone’s effect, changed so the proteins that normally hold IGF-1 back can’t bind it.

Studied inAnimal

Status: Not approved for any use.

In food-restricted rats, a week of infusion kept body weight 3 to 8% higher but didn’t preserve muscle protein (Tomas et al., 2001). In pigs it lowered blood sugar 2 to 3 times more strongly than natural IGF-1, and for longer (Tomas et al., 1997). An anti-doping lab found a lab-research version, with a purification tag still attached, in a black-market vial (Kohler et al., 2010). We haven’t found a published study in people.

Read the IGF-1 LR3 summary →

IGF-1 DES

A shortened form of IGF-1, missing its first three amino acids, that occurs naturally in human brain and in colostrum.

Studied inCellAnimal

Status: Not approved for any use.

In cell studies it is about 10 times more potent than IGF-1; in animals its clearest effects were on the gut, and a 1996 review noted it had not yet been evaluated for any clinical use (Ballard et al., 1996). In pigs it was the strongest of the IGF-1 variants at lowering blood sugar (Tomas et al., 1997). We haven’t found a published study in people.

Full summary in progress.

MGF (mechano growth factor)

A 24-amino-acid piece of a form of IGF-1 that muscle makes after exercise or injury, made in the lab as a synthetic peptide.

Studied inCellAnimal

Status: Not approved for any use.

In human muscle-cell cultures it increased the number of muscle stem cells (Ates et al., 2007). When scientists at two drug companies tried to repeat this kind of result, MGF had no effect on human or mouse muscle cells (Fornaro et al., 2014). We haven’t found a published study in people.

Full summary in progress.

PEG-MGF

MGF with a polyethylene glycol (PEG) chain attached, a common way to make a peptide last longer in the body.

Studied inNo published studies found

Status: Not approved for any use. The FDA lists it among compounding substances with safety concerns and says it has not identified any data on people exposed to PEG-MGF by any route (FDA, 2026).

We haven’t found a published study of PEG-MGF itself, in cells, animals or people. Research on unmodified MGF is mixed: see MGF above.

Full summary in progress.

Follistatin-344

A form of follistatin, a protein (not a short peptide) the body makes that binds myostatin, the signal that limits muscle size.

Studied inAnimalHuman

Status: Not approved for any use.

In people it has only been studied as gene therapy injected into the thigh muscles. In 6 men with Becker muscular dystrophy, 4 walked farther in 6 minutes (Mendell et al., 2015). A second 6-person study reported gains in inclusion body myositis; a critic said its design, with no randomized control group, couldn’t support that claim (Greenberg, 2017). We haven’t found a study of injected follistatin protein for muscle in people.

Full summary in progress.

ACE-031

A lab-made protein that acts as a decoy receptor, soaking up myostatin and related signals that limit muscle growth.

Studied inAnimalHuman

Status: Not approved for any use. Its trial in boys with Duchenne muscular dystrophy was stopped early over safety concerns.

At the highest dose, one injection raised lean mass 3.3% and thigh muscle volume 5.1% after 29 days in 48 healthy postmenopausal women (Attie et al., 2013). In boys with Duchenne muscular dystrophy, the trial was stopped over nosebleeds and small dilated blood vessels (Campbell et al., 2017).

Full summary in progress.

Before you compare them

  • More lean mass isn’t more strength. Growth hormone itself added lean mass in fit young adults without improving strength (Liu et al., 2008).
  • Human data are thin. Only ACE-031 and follistatin (as gene therapy) have been studied in people, mostly in people with muscle disease.
  • None of the six is approved for any use, and the FDA lists PEG-MGF among compounding substances with safety concerns.
  • All six are banned in sport at all times. The World Anti-Doping Agency lists IGF-1 and its analogues and mechano growth factors as banned growth factors, and names follistatin and ACE-031 as banned myostatin blockers (WADA, 2026).

New to reading studies? Our guide to how to read a peptide study explains what cell, animal and human evidence can and can’t tell you.

Questions

Which peptides are best for muscle growth?

No study has compared them, and we haven’t found a study of any of them in people doing strength training. More lean mass also isn’t the same as more strength: in trials of growth hormone itself in fit young adults, lean mass rose 2.1 kg (4.6 lb) but strength didn’t improve (Liu et al., 2008). In a 1-year trial of MK-677, a lab-made chemical taken as a pill, not a peptide, fat-free mass rose 1.1 kg (2.4 lb) in healthy older adults while it fell 0.5 kg (1.1 lb) on placebo, with no change in strength or function (Nass et al., 2008). A small study of sermorelin in 11 older men, without a placebo group, found 2 of 6 strength measures improved (Vittone et al., 1997).

What is the downside of taking these peptides?

For most of them, too few people have taken them to know. The signals so far: ACE-031’s trial in boys was stopped over nosebleeds and small dilated blood vessels (Campbell et al., 2017); IGF-1 variants lowered blood sugar more strongly and for longer than natural IGF-1 in pigs and marmoset monkeys (Tomas et al., 1997); and the FDA says it has no data on people exposed to PEG-MGF (FDA, 2026).

Are peptides safer than steroids?

We haven’t found a study comparing any of these compounds with anabolic steroids, so there’s no evidence that they’re safer. Of the six on this page, only ACE-031 and follistatin gene therapy have safety data from people, all from small trials.

Sources

  1. Tomas FM, et al. Insulin-like growth factor-I (IGF-I) analogue, LR(3)IGF-I, ameliorates the loss of body weight but not of skeletal muscle during food restriction. Growth Horm IGF Res. 2001;11(2):92-103. PubMed 11472075
  2. Tomas FM, et al. IGF-I variants which bind poorly to IGF-binding proteins show more potent and prolonged hypoglycaemic action than native IGF-I in pigs and marmoset monkeys. J Endocrinol. 1997;155(2):377-86. PubMed 9415072
  3. Kohler M, et al. Detection of His-tagged Long-R³-IGF-I in a black market product. Growth Horm IGF Res. 2010;20(5):386-90. PubMed 20675162
  4. Ballard FJ, et al. Des(1-3)IGF-I: a truncated form of insulin-like growth factor-I. Int J Biochem Cell Biol. 1996;28(10):1085-7. PubMed 8930132
  5. Ates K, et al. The IGF-I splice variant MGF increases progenitor cells in ALS, dystrophic, and normal muscle. FEBS Lett. 2007;581(14):2727-32. PubMed 17531227
  6. Fornaro M, et al. Mechano-growth factor peptide, the COOH terminus of unprocessed insulin-like growth factor 1, has no apparent effect on myoblasts or primary muscle stem cells. Am J Physiol Endocrinol Metab. 2014;306(2):E150-6. PubMed 24253050
  7. U.S. Food and Drug Administration. Safety risks associated with certain bulk drug substances nominated for use in compounding. Content current as of April 22, 2026. FDA page
  8. Mendell JR, et al. A phase 1/2a follistatin gene therapy trial for becker muscular dystrophy. Mol Ther. 2015;23(1):192-201. PubMed 25322757
  9. Greenberg SA. Unfounded Claims of Improved Functional Outcomes Attributed to Follistatin Gene Therapy in Inclusion Body Myositis. Mol Ther. 2017;25(10):2235-7. PubMed 28927986
  10. Attie KM, et al. A single ascending-dose study of muscle regulator ACE-031 in healthy volunteers. Muscle Nerve. 2013;47(3):416-23. PubMed 23169607
  11. Campbell C, et al. Myostatin inhibitor ACE-031 treatment of ambulatory boys with Duchenne muscular dystrophy: Results of a randomized, placebo-controlled clinical trial. Muscle Nerve. 2017;55(4):458-64. PubMed 27462804
  12. Liu H, et al. Systematic review: the effects of growth hormone on athletic performance. Ann Intern Med. 2008;148(10):747-58. PubMed 18347346
  13. Nass R, et al. Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults: a randomized trial. Ann Intern Med. 2008;149(9):601-11. PubMed 18981485
  14. Vittone J, et al. Effects of single nightly injections of growth hormone-releasing hormone (GHRH 1-29) in healthy elderly men. Metabolism. 1997;46(1):89-96. PubMed 9005976
  15. World Anti-Doping Agency. 2026 Prohibited List, sections S2.3 and S4.3. WADA document

Last reviewed Nov 3, 2026 by Reed Calder. Nothing here is medical advice; see our medical disclaimer. Found a mistake? Email editors@peptideresearchstudy.com.

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