Peptides for muscle growth: the tier nobody can fill

Tesamorelin

Tesamorelin is a growth-hormone-releasing factor analog with a real, current FDA approval as Egrifta — and the approved use is reducing excess visceral abdominal fat in HIV-infected patients with lipodystrophy. Its evidence base is the strongest of anything on this page: two multicenter, double-blind, placebo-controlled Phase 3 trials pooling 806 patients, published in the Journal of Clinical Endocrinology & Metabolism (2010).

That trial did report increased lean body mass alongside the visceral-fat reduction it was designed to measure — which is the fact that gets clipped and reposted. What gets left off is the population and the indication. This was ART-treated HIV patients with a specific fat-redistribution syndrome, not healthy adults training for size, and the effect required continued dosing: stopping the drug let the visceral fat come back.

Our full evidence review, including how it compares against the GH-axis compound this site actually ranks providers for: sermorelin vs tesamorelin, the tesamorelin evidence review and what its FDA label says about dosing.

MK-677 (ibutamoren)

MK-677 has the best human evidence on this page, and it is worth reading in full rather than in the half that gets quoted. A two-year, 65-patient, double-blind, placebo-controlled RCT in adults aged 60–81, published in Annals of Internal Medicine (2008), found that 25 mg/day raised GH and IGF-I to young-adult levels and increased fat-free mass.

That is where most pages stop. The same trial also found no improvement in strength and no improvement in function, and no significant reduction in visceral or total fat mass. More lean tissue on a scan, no more capability in the person carrying it, over two years. A second RCT in patients recovering from hip fracture, published in Archives of Gerontology and Geriatrics (2011), tested it in exactly the setting where more strength would matter most.

Two more things belong next to the number: MK-677 raises fasting glucose and reduces insulin sensitivity, and a separate trial was stopped early over a heart-failure signal. And it is not a peptide — it is an orally active non-peptide ghrelin mimetic, which is why it appears in searches for peptides and in no pharmacy's peptide catalog. The full picture is in our MK-677 evidence review.

Bimagrumab

Bimagrumab blocks the activin type II receptor, the switch myostatin acts through to limit muscle growth. A Phase 2 randomized trial in adults with type 2 diabetes and obesity, published in JAMA Network Open (2021), produced the pattern everyone wants: fat down, lean mass up. That is a real, randomized, peer-reviewed result on a hard body-composition endpoint.

Two caveats decide where it sits. Its pivotal trial in a muscle-wasting disease — RESILIENT, in sporadic inclusion body myositis — did not meet its primary endpoint (6-minute walk distance), and its long-term extension was terminated early as a result. More lean mass again did not become more capability. And bimagrumab is a monoclonal antibody, not a peptide: no compounding pharmacy makes it, no telehealth clinic prescribes it, and nothing sold as a “myostatin inhibitor peptide” is this drug.

Where it genuinely matters is a different question this site covers: preserving lean mass during GLP-1 weight loss, where a meaningful share of the weight lost is muscle.

Sermorelin

Sermorelin is the compound in this group you can most easily get a prescription for, and the one this site ranks providers for. It is a GHRH analog: it prompts your own pituitary to release growth hormone rather than supplying GH directly. Its foundational human evidence is two randomized, placebo-controlled, double-blind ascending-dose studies, 28 and 49 days long, in healthy adults aged 21 to 61.

Those trials measured what they were built to measure: that the drug raises GH and IGF-1. They were not designed to measure body composition, strength, or sleep, and they did not. Sermorelin's only FDA-approved product is discontinued, and its approval was for pediatric growth-hormone deficiency — a different population than the healthy midlife adults it is sold to now.

That is a narrower claim than the marketing, and it is still the most defensible position in this group. Full detail: sermorelin vs ipamorelin vs CJC-1295, is sermorelin safe, and what “before and after” actually shows.

CJC-1295

CJC-1295 has genuinely good human biomarker data — better than most of this page. A placebo-controlled trial in the Journal of Clinical Endocrinology & Metabolism (2006) confirmed that it produces sustained elevation of GH and IGF-1 in healthy adults, which is a real pharmacological effect proven in real people.

There is no published trial testing whether that elevation produces the body-composition outcome it is marketed for. The evidence establishes the mechanism works and stops before the question you are actually asking. See our CJC-1295 review and the CJC-1295 + ipamorelin combination review.

Ipamorelin

Ipamorelin is sold in the same breath as sermorelin and CJC-1295, usually as the “cleaner” option. Exactly one randomized, placebo-controlled human trial of ipamorelin tested a clinical outcome, and it was not about muscle: 114 patients recovering from bowel-resection surgery, dosed intravenously, with postoperative ileus as the target, published in the International Journal of Colorectal Disease (2014). It missed — no significant difference from placebo on the key or secondary efficacy endpoints.

Searching the wider literature for a controlled trial of ipamorelin for body composition, fat loss, or aging returns nothing. What exists instead is a body of anti-doping detection papers that use it as a reference compound. It is well tolerated — the trial above found fewer adverse events on ipamorelin than on placebo — it simply has no muscle-growth evidence to weigh. Full review: what the ipamorelin evidence actually shows.

Follistatin-344

Follistatin blocks myostatin, and the myostatin story is genuinely compelling — which is why this compound sells. The distinction that decides everything: every positive human result for follistatin comes from gene therapy — a viral or plasmid vector that makes a patient's own muscle cells produce the protein internally — in two rare muscle-wasting diseases, including a 2017 Molecular Therapy trial in sporadic inclusion body myositis. That is a completely different intervention from injecting the recombinant protein, which is what is actually sold.

There is a published harm signal attached to the injected version specifically — a peer-reviewed case series of male bodybuilders using exactly this product. Our follistatin-344 evidence review covers both sides in full.

IGF-1 LR3

IGF-1 LR3 is a modified form of insulin-like growth factor 1, engineered to resist the binding proteins that normally clear it. The entire evidence position fits in one sentence: no human study has ever administered IGF-1 LR3 to a person, at any dose, by any route.

That means there is no human data on its half-life, no established dose, and no safety data — including on hypoglycemia risk, the obvious hazard for a compound acting on the insulin/IGF axis. Any dosing protocol you find for it was written by someone extrapolating, not reporting. See our IGF-1 LR3 evidence review.