Ibutamoren is an orally active growth hormone secretagogue, better known by the development code MK-677 (also written L-163,191). It is not a peptide, despite often being grouped with them; it is a small synthetic molecule that mimics ghrelin, the stomach-derived "hunger hormone." Merck developed it in the 1990s, and rights later passed to other companies including Lumos Pharma. It has never been approved by the FDA, EMA, or any other health authority. CAS number is 159634-47-6.
How it works
Ibutamoren binds and activates the growth hormone secretagogue receptor (GHSR-1a), the same receptor that ghrelin acts on, which sits in the hypothalamus and pituitary. Activating it stimulates the pituitary to release growth hormone (GH) in pulses, and the rise in GH drives a sustained increase in insulin-like growth factor 1 (IGF-1). Because the compound is orally active and long-acting, a single daily dose can keep IGF-1 elevated across 24 hours. Per the PubChem record, it is described as a potent, selective, non-peptide ghrelin-receptor agonist.
The effect on IGF-1 is well documented. In one large 12-month trial, a 25 mg daily dose raised serum IGF-1 by about 60% at six weeks and roughly 73% at one year (Sevigny et al., *Neurology*, 2008).
What the human research found
Unlike many compounds sold as "research peptides," ibutamoren actually went through real clinical trials. The results are mixed, and that history is the most useful thing a reader can know.
- Body composition in older adults. A randomized, placebo-controlled trial in healthy older adults tested 25 mg daily for up to a year. It raised IGF-1 and increased fat-free mass by roughly 1 kg, but it did not improve muscle strength or function, and it worsened insulin sensitivity and raised blood glucose (Nass et al., *Annals of Internal Medicine*, 2008). The matching trial record is NCT00474279.
- Alzheimer's disease. A double-blind study randomized 563 patients with mild-to-moderate Alzheimer's to MK-677 25 mg or placebo for 12 months. The drug hit its biological target, raising IGF-1 as expected, but it did not slow cognitive or functional decline on any of the standard measures. The authors concluded it was ineffective for that purpose (Sevigny et al., *Neurology*, 2008).
- Catabolic states. Earlier work showed MK-677 could reverse diet-induced protein loss (nitrogen wasting) in healthy volunteers, one of the reasons it drew interest for muscle-wasting conditions (Murphy et al., *J Clin Endocrinol Metab*, 1998).
Decades of trials never produced an approved indication. Reported issues across studies include increased appetite, fluid retention, raised blood glucose and reduced insulin sensitivity, and elevated IGF-1, which is why the drug has not cleared the bar for any therapeutic use.
Regulatory and anti-doping status
Ibutamoren is an investigational drug, not a medicine and not a dietary-supplement ingredient. The U.S. Department of Defense's Operation Supplement Safety notes it is unapproved and not legal for use in supplements or consumer products (OPSS). Products sold online as MK-677 are unregulated, so identity, dose, and purity are not guaranteed.
It is banned in sport. The World Anti-Doping Agency lists growth hormone secretagogues, including ibutamoren, under section S2 (Peptide Hormones, Growth Factors, Related Substances and Mimetics), prohibited at all times in and out of competition. Athletes subject to testing should treat it as a doping violation.
The quality angle for buyers
Because nothing on the gray market is regulated, what is in a vial labeled "MK-677" is an open question. Independent third-party lab testing is the only way to check identity and purity, and a current Certificate of Analysis (COA) tied to a specific batch matters more here than any marketing claim. peptideone aggregates vendor COAs and independent rater signals so these can be compared, but a COA confirms what a chemical is, not that it is safe or effective to take.
This page is informational only. Ibutamoren is research use only, is not approved for human consumption, and nothing here is medical or dosing advice.