You have probably seen peptides sold as a shortcut to muscle. Most of them do one thing. They push your pituitary to release more growth hormone.
So the real question is simple. When trials raised growth hormone this way, did people gain muscle and strength? How the drugs work is covered in growth hormone peptides. This page sticks to what the trials measured.
Lean mass is not the same as muscle
Start with one word you will see in every trial: lean mass. It means everything in your body that is not fat. That includes muscle, but also water, organs and bone.
Growth hormone can make the body hold extra fluid, and swelling was more common on it in trials [5]. So a rise in lean mass can be partly water. That is why strength matters. It tells you whether the new lean mass does any work.
The longest trial: a two-year pill study
The longest trial used MK-677, an oral drug that acts on the ghrelin receptor. It enrolled 65 healthy adults aged 60 to 81, on 25 mg a day or placebo [1].
After a year, fat-free mass rose 1.1 kg on the drug and fell 0.5 kg on placebo (P < 0.001). Body weight rose 2.7 kg against 0.8 kg [1].
Here is the trade-off. The extra fat-free mass did not change strength or function. Fasting blood sugar rose, insulin sensitivity fell, and people reported more appetite, leg swelling and muscle pain [1].
An earlier trial gave the same dose to 24 obese men aged 18 to 50 for 8 weeks [2]. Fat-free mass rose, but body fat did not change. A glucose tolerance test showed worse blood sugar handling.
The largest trial: capromorelin
The largest trial tested capromorelin, another oral ghrelin-receptor drug. It randomized 395 adults aged 65 to 84 with mild limits on their mobility [3].
At 6 months, lean body mass rose 1.4 kg on capromorelin against 0.3 kg on placebo (P = 0.001). Tandem walking improved by 0.9 seconds. By 12 months, stair climbing had improved too [3].
This is the one trial where function moved. It came with fatigue, insomnia and small rises in blood sugar and HbA1c. The trial was stopped early, under rules set before it began [3].
A growth-hormone-releasing hormone analog
Sermorelin and its relatives act on a different receptor. The closest trial to the muscle question used a similar analog in 19 adults aged 55 to 71 [4].
Each person injected 10 micrograms per kilogram nightly for 16 weeks. Lean body mass rose in the men, but not in the women. Strength was not among the outcomes it reported [4].
| Trial | Who | Lean mass | Strength or function |
|---|---|---|---|
| MK-677, 1 year | 65 adults aged 60–81 | +1.1 kg vs −0.5 kg | No change |
| Capromorelin, 6–12 months | 395 adults aged 65–84 | +1.4 kg vs +0.3 kg | Walking and stairs improved |
| GHRH analog, 16 weeks | 19 adults aged 55–71 | Rose in men only | Not reported |
| Growth hormone, meta-analysis | 303 treated young adults | +2.1 kg | No clear gain |
What about young, fit people?
If you are younger than these volunteers, the best data come from growth hormone itself, not from peptides.
One review pooled 27 study groups with 303 fit adults given growth hormone [5]. Lean mass rose 2.1 kg (95% CI 1.3 to 2.9). Strength and exercise capacity did not seem to improve, and swelling and fatigue were more common.
A later meta-analysis of 11 trials found the same split [6]. Lean mass rose and fat fell. Muscle strength did not change over weeks to months (p = 0.36).
If injected growth hormone does not build strength in young adults, a drug that raises it less is unlikely to. That is a reasonable inference, not a tested result.
The popular blends
CJC-1295 is often paired with ipamorelin and marketed for muscle. A 2026 review for orthopedic surgeons found the muscle data for that pair are limited to mouse studies [7]. The human record is in CJC 1295 and ipamorelin.
Ipamorelin has never been tested for muscle in people. Its safety record is in ipamorelin side effects.
What this means for you
The trials point one way. These drugs can add a kilogram or so of lean mass. They rarely add strength.
The costs show up in blood sugar, swelling and appetite. And most of these drugs are research-only. The FDA flags ibutamoren, ipamorelin and CJC-1295 for safety concerns [8].
If recovery and strength are your goal, the recovery page sets out the options with human evidence behind them. Start at the recovery goal page.