MK-677, sold under the name ibutamoren, is an orally active ghrelin mimetic that raises growth hormone by acting on the ghrelin receptor rather than the GHRH receptor that sermorelin uses.
It was developed as a pharmaceutical and taken into real trials, so its adverse-effect record is better documented than most peptides sold online. That record is also the reason regulators treat it the way they do.
The class it belongs to, and how it differs from the injected peptides, is set out in growth hormone peptides.
The finding that ended a trial
The most serious signal comes from a phase IIb trial in 123 elderly patients recovering from hip fracture[1]. They received 25 mg a day of MK-0677 or placebo, with functional performance and blood markers as the primary outcomes.
The trial was terminated early because of a safety signal of congestive heart failure in a limited number of patients. The authors' own summary is that the drug has an unfavorable safety profile in that population.
The efficacy side was thin. IGF-1 rose by 51.4 ng/mL against placebo, 95% CI 34.42 to 68.44, P < 0.001. Gait speed improved by a 0.7-point difference in means, 95% CI 0.17 to 1.28, P = 0.011. Stair-climbing power did not separate, 95% CI −10.95 to 35.88, P = 0.292.
An earlier and larger trial in the same setting, 161 hip-fracture patients across 13 medical centers, had already found the same split [3]. IGF-I rose 84% on the drug (95% CI 63 to 107) against 17% on placebo (95% CI 8 to 28), with no significant difference in functional performance.
That trial excluded anyone with congestive heart failure at entry, which is worth noting when reading its cleaner safety record.
The metabolic effects, which are consistent
The longest trial gave 25 mg a day to 65 healthy adults aged 60 to 81 for two years, double-blind and placebo-controlled [2].
| Measure | What happened |
|---|---|
| Fat-free mass | Up 1.1 kg (95% CI 0.7 to 1.5) vs down 0.5 kg on placebo, P < 0.001 |
| Body weight | Up 2.7 kg (95% CI 2.0 to 3.5) vs 0.8 kg on placebo, P = 0.003 |
| Limb fat | Up 1.1 kg vs 0.24 kg on placebo, P = 0.001 |
| Fasting glucose | Up about 5 mg/dL, P = 0.015, with insulin sensitivity falling |
| Cortisol | Up 47 nmol/L (95% CI 28 to 71), P = 0.020 |
| Strength and function | No change despite the extra fat-free mass |
| Most frequent side effects | Increased appetite, transient mild lower-extremity edema, muscle pain |
The appetite increase subsided after a few months, and the swelling and muscle pain are described as transient and mild. Those are the effects most users report, and they match the trial record.
The glucose finding is the one that recurs. A four-week dose-ranging trial in 32 healthy adults aged 64 to 81 found fasting glucose rising from 5.4 to 6.8 mmol/L on 25 mg a day [4].
That trial also reported prolactin rising 23%, though it stayed inside the normal range, and cortisol unchanged. Its IGF-I result was the headline at the time: 141 µg/L at baseline rising to 265 µg/L at four weeks.
Note what the two-year trial found about that extra lean mass. It did not translate into strength or function, which is the same disconnect described in peptides for muscle growth.
The sleep effect, and its sample size
One frequently quoted result is a crossover study of sleep architecture [5]. Eight young adults aged 18 to 30 took 5 mg, 25 mg or placebo at bedtime for seven days each. Six adults aged 65 to 71 took 2 mg, then 25 mg, for 14 days each.
In the young group, 25 mg increased stage IV sleep by roughly 50% and REM sleep by more than 20% against placebo. In the older group, REM sleep rose by nearly 50% and REM latency fell.
Fourteen people in total took part. That is a real finding in a small sample, not a demonstrated treatment for poor sleep.
What has never been measured
Every trial above studied a defined patient group, at 25 mg or less, for two years at most. None studied a healthy adult taking it for body composition, which is what it is sold for.
No trial followed cardiac outcomes long enough to characterize the heart failure signal, because the trial that found it was stopped. The glucose effect was never followed to a diabetes endpoint either.
Material sold as MK-677 online is also not a pharmaceutical product, so purity and content are unverified. The general version of that problem is in are peptides safe.
Putting it together
The recorded side effects fall into three groups. Appetite and fluid effects are common and mild, the metabolic effects are consistent and unwanted, and one cardiac signal was serious enough to stop a trial.
That last one is what regulators acted on, and it is the reason this compound cannot be compounded lawfully. The comparable record for an injected secretagogue is in ipamorelin side effects, and the rest of this goal is on the recovery hub.