Peptides for muscle growth: what the human trials actually show

No peptide is approved to build muscle, and none has been shown in a controlled human trial to make healthy people stronger. What exists is a small set of trials where drugs that raise growth hormone (GH) also raised lean body mass, mostly in older adults or in people with HIV, and in which strength and function did not follow. That gap between the hormone number and the thing you can actually do is the whole story of this category. The goals overview sits alongside this page for the other outcomes people search.

What human trials show, compound by compound

Two patterns run through every row. The gains are about 1 to 2 kg, and wherever strength or function was measured, it did not move with the lean mass.

Notice what the diagram implies about the whole category. Every one of these compounds asks the pituitary to release more of its own growth hormone. That makes them weaker levers than growth hormone itself, and growth hormone itself did not improve strength in fit adults.

What people hope for, and what the trials delivered

The hope, as the marketing frames it, is a body that responds like a younger one: more muscle for the same training, faster recovery, less fat, deeper sleep. Set that against the measurements.

• More muscle. Delivered as about 1 kg of lean mass a year in older adults, or 1.2 to 1.3 kg over 26 weeks in people being treated for HIV lipodystrophy. For scale, a kilogram of lean mass is roughly what a committed beginner adds in a couple of months of lifting.
• More strength. Not delivered in any trial that measured it.
• Faster recovery. No controlled human trial has tested recovery from training for any of these compounds.
• Less fat. The year-long MK-677 trial found no change in visceral or total fat, and limb fat rose. Tesamorelin does reduce visceral fat, in the one patient group it is approved for, and its label states it has a weight-neutral effect.
• Keeping the gains. In the tesamorelin trials, people switched to placebo lost 1.8 kg and 1.7 kg of lean mass over the following 26 weeks, which is more than they had gained. Whatever these drugs do, they do it only while you keep taking them.

Lean mass is not the same as muscle strength

Lean body mass includes body water, not just muscle. GH-raising drugs cause fluid retention: the tesamorelin label lists swelling, joint pain and carpal tunnel syndrome, and the growth hormone review found more soft tissue swelling in treated athletes. Some of a lean-mass gain may therefore be water rather than contractile muscle. In the MK-677 trial, total body weight rose 2.7 kg against 0.8 kg on placebo, more than twice the fat-free mass gain.

The best direct look at muscle tissue comes from tesamorelin. A secondary analysis of its phase 3 trials, limited to patients whose belly fat responded, found small increases in the area and density of trunk muscles on CT scans. Whether that changes anything in daily life was not tested; a trial combining tesamorelin with exercise in older adults with HIV is under way.

IGF-1: the number these drugs move

IGF-1 (insulin-like growth factor 1) is the hormone the liver releases in response to GH, and it carries much of GH’s effect on tissue. Tesamorelin raised IGF-1 by 81% in its NEJM trial. CJC-1295 raised it 1.5 to 3 fold after a single injection. MK-677 raised it 60% to 73% in the Alzheimer’s trial. That is the mechanism sellers point to, and a clinic can show you a lab result that moved.

It is also the main concern. The tesamorelin label says “the effects of prolonged elevations in IGF-1 levels are unknown,” tells prescribers to monitor it, and requires any cancer to be inactive and treated before starting. A higher IGF-1 is not a result. It is evidence that the drug did something, plus a reason to watch.

What is actually approved for muscle

Nothing is approved for building muscle in a healthy person. Three approved treatments touch the territory, each tied to a diagnosis:

The pattern is consistent: when a hormone is genuinely missing, replacing it helps, and the approvals are written around that. None of these is a performance drug, and every one of them has a label precisely because somebody had to prove what it does and disclose what it costs you.

Banned in sport

WADA’s Prohibited List bans all of these at all times, in and out of competition, under class S2, and the 2027 list that takes effect January 1, 2027 keeps them there. CJC-1295, sermorelin and tesamorelin are named as GHRH analogues. Ipamorelin and ibutamoren (MK-677) are named as GH secretagogues. Growth hormone fragments such as AOD-9604 and TB-500 sit in the same class, and BPC-157 is named under class S0, for substances with no approval for human use anywhere. The 2027 list also names “peptides” in general under S0, so an unlisted name is no protection.

Risks reported in the trials

• Heart failure. The hip-fracture trial of MK-677 was stopped early over a congestive heart failure signal, and its authors concluded the drug had “an unfavorable safety profile in this patient population.” FDA cites that risk as the reason ibutamoren stays in category 2.
• Blood sugar. MK-677 raised fasting glucose by about 5 mg/dL and lowered insulin sensitivity over a year. The tesamorelin label warns that glucose intolerance or diabetes may develop.
• Fluid and joints. Swelling, joint pain, muscle pain and carpal tunnel symptoms appear in the tesamorelin label and the MK-677 trial.
• Cancer history. GH and IGF-1 are growth factors. Tesamorelin is contraindicated in active malignancy, and somatropin labels list an increased risk of neoplasm among their warnings.
• Pregnancy. Tesamorelin is contraindicated in pregnancy.
• Unknowns for the unapproved ones. CJC-1295 and ipamorelin were placed in FDA’s category 2 (significant safety risks) in September 2023. Their nominations were later withdrawn, which left them with no compounding route at all. There is no long-term human safety data for either, and FDA found no safety data at all for ipamorelin given under the skin.
• What is in the vial. Research-market products carry no verified identity, purity or sterility, and FDA has found mismatched sequences and CAS numbers in supplier listings.

Legal status in plain terms

Tesamorelin is a prescription drug approved for one indication. Sermorelin is compounded by pharmacies on the basis that it was once part of an approved drug. CJC-1295, ipamorelin and MK-677 have no approval and no compounding route; the FDA status tracker has the dates.

One thing did change recently. On October 28, 2026, HHS issued an interim enforcement discretion policy, published in the Federal Register on October 30. As of November 2, 2026, HHS says it does not intend to take enforcement action against a state-licensed pharmacy, federal facility or licensed physician compounding one of six peptides under section 503A, when ten conditions are met, until rulemaking decides whether each belongs on the bulks list. The six are BPC-157, TB-500, MOTS-c, epitalon, KPV and semax, each with its own limits on form and route.

What that does and does not mean for this page:

• None of the six is FDA-approved, none is on the 503A bulks list, and no rule has been proposed. FDA has not reviewed any compounded product for safety, effectiveness or quality.
• Enforcement discretion is a choice not to enforce. The notice says the policy “does not establish any rights for any person and is not binding on HHS or the public,” and comments are open until November 13, 2026.
• The evidence has not changed. BPC-157 still has no published controlled human trial, and TB-500 none for muscle growth.
• Each product must contain a single active ingredient, so multi-peptide blends sold for muscle or recovery fall outside the policy even when every ingredient is on the list.
• The peptides most often sold for muscle, CJC-1295 and ipamorelin, are not on the list. Neither is MK-677, which is not a peptide.
• Research-use-only products gain nothing. Under 21 CFR 312.160 they may be shipped only for laboratory or animal tests, and FDA warning letters in 2026 treated that label as no defense when a product was sold for people. They are not legal to use on a person.

States can also be stricter than the federal policy. The peptide safety guide covers the wider picture.

What to do instead

This is the unglamorous part of the answer, and it is the part with the strongest evidence behind it.

• Train against resistance at least twice a week. CDC guidelines call for muscle-strengthening activity on “at least 2 days” a week, working all the major muscle groups: legs, hips, back, abdomen, chest, shoulders and arms.
• Eat enough protein. A meta-analysis of 49 randomized trials in 1,863 people found that protein supplementation during resistance training added 0.30 kg of fat-free mass and 2.49 kg to one-repetition-maximum strength. Total intakes above about 1.62 g per kg of body weight a day produced no further gains, so there is a ceiling worth knowing about.
• Consider creatine monohydrate. The International Society of Sports Nutrition’s position stand concludes that creatine improves high-intensity exercise performance and supports training adaptations, and that short-term and long-term use, up to 30 g a day for 5 years, is “safe and well-tolerated in healthy individuals.”
• Get the real cause checked. If you have lost muscle without trying, or you are exhausted and weak, that deserves a diagnosis. Low testosterone, thyroid disease, poorly controlled diabetes, kidney disease and cancer all cause muscle loss, and three of those have approved treatments that work.

Against those numbers, the peptide trials offered about 1 kg of lean mass, no measurable strength, a cost in blood sugar and fluid, and a loss of the gain on stopping. That comparison is the clearest argument this page can make.