MK-677 (Ibutamoren): Status, Evidence and Sellers

MK-677, also called ibutamoren, is sold on peptide menus, but it is a small synthetic molecule taken by mouth. Its developers at Merck described it as an orally active nonpeptide that mimics the growth-hormone-releasing peptides [1] [6]. It acts on the ghrelin receptor, a different receptor from the one sermorelin and CJC-1295 target, and pushes the pituitary to release more growth hormone, which raises IGF-1 [3] [6].

It is marketed to people who want more muscle, deeper sleep or protection against muscle loss while dieting. Unusually for this market, it went through real randomized trials in the 1990s and 2000s, including one that ran for two years [3]. Those trials show what it does to hormone levels and body composition fairly clearly, and they also show its costs.

FDA keeps ibutamoren mesylate in category 2, its group of bulk substances flagged for serious safety concerns, for 503A pharmacies and 503B outsourcing facilities alike, citing a heart-failure signal from a trial in older adults [8]. It is not one of the six peptides in the October 28, 2026 HHS policy.

Ghrelin is the hunger hormone released mostly by the stomach, and its receptor in the brain and pituitary also triggers growth hormone pulses. MK-677 binds that receptor, and taken once a day it keeps growth hormone output and IGF-1 higher for as long as people take it [2] [3]. The same action fits its most common side effect in the trials, more hunger, since the ghrelin receptor also drives appetite [3].

Growth hormone also works against insulin. That fits what the trials found: blood sugar control worsened on MK-677 [2] [3], which matters for anyone with diabetes or prediabetes.

The longest trial gave 65 healthy adults aged 60 to 81 either 25 mg of MK-677 or placebo once a day for up to two years. After a year, fat-free mass fell 0.5 kg on placebo and rose 1.1 kg on MK-677. Weight rose 2.7 kg against 0.8 kg, abdominal and total fat did not change, and the extra lean mass did not translate into any change in strength or function [3]. An eight-week trial in 24 obese men found the same pattern: IGF-1 up about 40% and fat-free mass up, with no fall in total or visceral fat [2].

The trials that tested outcomes people care about were disappointing. In 123 older adults recovering from hip fracture, MK-677 improved gait speed but not most other measures of function, and the trial was stopped early because of a safety signal of congestive heart failure [4]. In 563 people with Alzheimer disease it raised IGF-1 by 72.9% at a year and did nothing to slow the disease [5]. The study most often quoted by sellers enrolled eight dieting volunteers for a week of treatment and measured nitrogen balance, a lab estimate of protein retention, which moved from negative to positive [1].

Grade B: randomized trials agree that it raises growth hormone, IGF-1 and lean mass. None showed people getting stronger or moving better, and none tested whether healthy adults who train gain strength on it. Our evidence review covers the nitrogen-balance trial and the liver case in detail.

MK-677 has no approved dose for any use. Every trial above used 25 mg by mouth once a day [3] [4], and that is the only dose with a published human record of benefit and harm. Higher amounts sold online have no trial behind them.

Because FDA places ibutamoren in category 2 for both compounding routes, a US pharmacy or outsourcing facility has no pathway to supply it [8]. What buyers find is sold outside that system, as a supplement or research chemical [7], with nothing checking what is in the bottle.

In the two-year trial the most frequent side effects were an increase in appetite that faded over a few months and mild, temporary swelling of the legs and muscle pain. Fasting blood sugar rose by an average of 5 mg/dL, insulin sensitivity fell and cortisol rose [3]. The eight-week trial found impaired glucose tolerance at two and eight weeks [2].

The hip-fracture trial stopped early over congestive heart failure in a small number of patients, and its authors concluded that MK-677 had an unfavorable safety profile in that group [4]. That is the finding FDA cites for its category 2 listing [8]. A 2025 case report described liver inflammation in a healthy man in his early 30s after two months of use, which resolved after he stopped [7]. One case cannot give a rate, but liver tests are a sensible check for anyone who has taken it.

MK-677 is named on the World Anti-Doping Agency's 2026 Prohibited List as a growth hormone secretagogue, under section S2, and is banned in and out of competition [9].