Searches for this phrase mostly return lists of compounds with dosing attached. We left the dosing out and went to the trials. A handful measured lean mass or muscle volume, and the numbers are smaller and messier than the lists suggest. This page summarizes four of them and what each could not show. It reports published research and gives no advice, and the research vendors we review label their products for laboratory use only.
Do peptides build muscle?
The evidence is thin and mixed. Trials of growth hormone related compounds mostly measured hormone levels. The few that measured lean mass were small and short, and they enrolled older adults or people with a disease, which limits what they say about anyone else.
Four trials that measured lean mass or muscle
Swipe the table sideways to see every column.
| Trial | Who and how long | What changed | The catch |
|---|---|---|---|
| MK-677, 2008 (an oral ghrelin mimetic, not a peptide) | 65 healthy adults aged 60 to 81, one year | Fat-free mass fell 0.5 kg on placebo and rose 1.1 kg on MK-677 | No change in strength or function. Fasting glucose rose and insulin sensitivity fell. |
| Growth hormone releasing hormone analog, 1997 | 19 adults aged 55 to 71, 16 weeks on the analog | Lean body mass rose in men only | Tiny sample, and a relative of the vendor products rather than one of them. |
| Bimagrumab, 2019 (an antibody against activin type II receptors) | 67 people with COPD and low muscle mass, 24 weeks | Thigh muscle volume 5.0% higher at week 24 on bimagrumab, 1.3% lower on placebo | Walking distance did not improve. |
| Tirzepatide, SURMOUNT-1 body composition substudy, 2025 | 160 adults with obesity or overweight, 72 weeks | Lean mass fell 10.9% on tirzepatide and 2.6% on placebo | A weight loss trial. Eli Lilly employees wrote the paper. |
What the first three trials show
Each one measured a body composition number in a specific group, and none enrolled healthy young people who train. The MK-677 gain came with costs the paper reports: higher fasting glucose, lower insulin sensitivity, more appetite, and mild leg swelling and muscle pain. The FDA's compounding page lists ibutamoren in category 2 and cites a separate hip fracture trial that stopped early over a possible heart failure signal.
The bimagrumab result is the largest muscle change in the table, and it came from a drug that blocks a pathway, in people who had lost muscle to disease. The same paper reports no improvement in walking distance. More muscle on a scan and more function are separate findings, and the trials we read gave them separately.
What about the compounds vendors sell?
The trials above did not test the compounds on most ranking pages. The 2006 CJC-1295 trial measured growth hormone and IGF-I and did not report muscle, and the paper that introduced ipamorelin reports animal and cell work. Our post on the best peptides for muscle growth goes compound by compound, and the one on CJC-1295 and ipamorelin covers the most searched pair, and the one on IGF-1 LR3 covers the compound with the most buyer searches, and the one on myostatin inhibitors covers the drug trials behind follistatin, and the one on sermorelin vs tesamorelin covers the two approved-drug analogs, and the one on follistatin 344 covers the protein vendors list, and the one on peptides vs steroids covers how the law and the anti-doping rules treat both, and the one on growth hormone secretagogues sorts the compounds by receptor.
Lean mass in a tirzepatide weight loss trial
This is the result most relevant to readers who arrive from our tirzepatide pages. In the SURMOUNT-1 substudy, 160 of the 2,539 participants had DXA scans at baseline and at week 72. Body weight fell 21.3% on pooled tirzepatide doses and 5.3% on placebo, and fat mass fell 33.9% and 8.2%. About 75% of the weight lost was fat and about 25% was lean mass in both groups. The proportions held across most subgroups, though those were post hoc analyses. The abstract reports that split and says nothing about preventing the loss.
What none of this tells you about a research vial
No trial here tested a product bought from a research vendor. Results describe the specific drug and the specific people studied. For a vial labeled for laboratory use, the only thing a buyer can check is paperwork, and even that has limits. Start with our guide to spotting a fake COA and the walkthrough of how to read a peptide COA.
If you are researching tirzepatide
Core Power Peptides lists tirzepatide 50 mg at $320, marked down from $416 (). The listing states purity of at least 99% and says a certificate of analysis is available on request. We found no certificate on the page, and we have not tested the product. For BPC-157 and TB-500, see what is and is not known about BPC-157 and TB-500. Our tirzepatide page and the vendor review lay out the gaps. We earn a commission if you buy through the link below, and that is why we list what is missing.
Frequently asked questions
Do peptides build muscle?
The trials we found are small and mixed. One measured a 1.1 kg rise in fat-free mass over a year with MK-677, which is not a peptide, and saw no change in strength. Hormone studies did not measure muscle.
Does lean mass fall during tirzepatide weight loss?
In the SURMOUNT-1 substudy it fell 10.9% on tirzepatide against 2.6% on placebo, and about a quarter of the weight lost was lean mass. This site gives no medical advice.
Are these compounds allowed in competition?
The 2026 WADA list, as reproduced by the Cologne laboratory, names growth hormone releasing hormone analogs, secretagogues, IGF-1 and mechano growth factors. Tested athletes should read the current list.