Short answer: Testosterone has the clearest human data: in men with low testosterone, replacement added about 5 kg of lean mass in 10 weeks. Growth hormone peptides raise growth hormone, but muscle results in people are small and mixed, and IGF-1 LR3 has no published human studies. On GLP-1 drugs, about a quarter of weight lost in one scan study was lean mass.
| Compound | Best evidence | What it shows |
|---|---|---|
| Testosterone (cypionate, enanthate) | Approved for a different use | Approved to replace testosterone in men with diagnosed deficiency, not to build muscle. In 7 hypogonadal men, 10 weeks raised fat-free mass by 5.0 kg. |
| Sermorelin (GHRH 1-29) | Small or early human studies | In 9 older men, 16 weeks of a GHRH 1-29 analog raised lean body mass. In 11 older men, 6 weeks did not change DXA muscle. |
| Ipamorelin | Small or early human studies | Raises growth hormone in healthy men. We found no published human trial measuring muscle. |
| CJC-1295 | Small or early human studies | One dose raised IGF-1 1.5 to 3 times for 9 to 11 days in healthy adults. No muscle outcome was reported. |
| IGF-1 LR3 | No published studies found | We found no published human study of any kind. It is not approved for human use. |
"Animal or lab studies only" means no published human trial for this goal that we could find. Results in rats or cells often do not carry over to people. Compounds that are not FDA-approved have no tested label for dose, purity or safety.
The Depo-Testosterone label approves it for replacement therapy in the male in conditions associated with symptoms of deficiency, and says safety and effectiveness in age-related low testosterone have not been established. It is not approved for muscle building.
In men with low testosterone (Bhasin 1997, 7 men, 10 weeks on a set diet), replacement raised fat-free mass from 56.0 to 60.9 kg and enlarged arm and thigh muscle. In healthy young men whose own testosterone was shut down (Bhasin 2001, 61 men, 20 weeks), lean mass rose with dose: 3.4 kg at 125 mg weekly up to 7.9 kg at 600 mg. Those higher doses gave blood levels far above normal and are not a treatment.
These are growth hormone secretagogues: they make the pituitary release more of your own growth hormone. That they raise growth hormone is well shown. That this builds muscle in people is not.
A 2026 review of peptides used for performance concluded that rigorous human safety data are scarce and that there is potential for serious harm.
Some lean mass is lost with any large weight loss. In a SURMOUNT-1 substudy (160 people, DXA scans, 72 weeks), tirzepatide lowered lean mass by 5.6 kg (10.9%) and fat mass by 15.9 kg. About 74% of the weight lost was fat and 26% lean, nearly the same split as placebo. The authors cite about 40% lean in a STEP 1 semaglutide scan substudy.
Lean mass on DXA includes water and organs, not only muscle, and the substudy did not measure strength or physical function.
Terms on this page: Growth hormone secretagogue · Hematocrit · Testosterone ester · Research use only (RUO)