MK-677 (Ibutamoren)
Also known as: ibutamoren, MK-0677
An orally-active GH secretagogue with genuine trial data, one that raised hormones and lean mass but not function, and was never approved.
What it is
MK-677 (ibutamoren) is an orally-active growth-hormone secretagogue. It raises growth hormone by mimicking the hunger hormone ghrelin. It is grouped with the GH peptides here, but with an important caveat: it is not itself a peptide. It is a small molecule you can swallow, which is part of why it is so widely discussed.
Composition
A synthetic, orally-available non-peptide molecule that acts at the ghrelin (growth-hormone secretagogue) receptor. Unlike the injectable GHRH peptides, its oral activity is its defining feature.
Proposed mechanism
By activating the ghrelin receptor, it prompts the pituitary to release more growth hormone and raises IGF-1, mimicking a natural hunger-linked signal for GH release.
Claimed benefits
Muscle gain, fat loss, better sleep, improved recovery and skin, a broad “more growth hormone is good” pitch. The trial evidence is more sobering than the claims.
What the evidence shows
Silver· human data. There is genuine human data, unusually for this section. A two-year randomised trial in healthy older adults (Nass et al., Annals of Internal Medicine, 2008) found MK-677 reliably restored GH and IGF-1 toward younger-adult levels and increased fat-free mass by about 1.1 kg. Crucially, that same trial found no improvement in strength or physical function, the hormone changes did not translate into the functional benefits people assume. So: real biological effect, unconvincing real-world payoff, and no approval.
Legal & regulatory status
Not an approved medicine, its clinical development did not lead to approval. It is sold as a research chemical. It is on the WADA prohibited list as a growth-hormone secretagogue and is banned in and out of competition.
Known risks & unknowns
Reported effects include increased appetite, water retention, and, notably, raised blood glucose and reduced insulin sensitivity, which matter for anyone with metabolic risk. Long-term safety in healthy people using it for physique goals is not established, and driving GH/IGF-1 chronically has theoretical risks that trials this size cannot rule out.
Sources
Frequently asked questions
- Is MK-677 a peptide?
- No, this is an important distinction. MK-677 (ibutamoren) is a small, orally-active molecule that mimics the hormone ghrelin at its receptor. It is grouped with GH secretagogues because it raises growth hormone, but it is not itself a peptide.
- Does MK-677 actually work?
- It reliably raises GH and IGF-1 to more youthful levels, and a two-year trial in healthy older adults increased fat-free mass by about 1.1 kg. But that same trial found no improvement in strength or function, and it is not an approved medicine, and the hormone changes did not translate into the benefits people assume.
- What are the risks?
- Reported effects include increased appetite, water retention, raised blood glucose and reduced insulin sensitivity. Long-term safety in healthy people using it for physique goals is not established.
- Is MK-677 banned in sport?
- Yes. It is on the WADA prohibited list as a growth-hormone secretagogue and is banned in and out of competition.
Related compounds
- Tesamorelin (Gold)
An evidence-tiered explainer on tesamorelin (Egrifta): the one GH-releasing peptide with FDA approval and robust trials, for a medical use, not fitness.
- HGH Fragment 176-191 (Unproven)
An evidence-tiered explainer on HGH Fragment 176-191: a growth-hormone fragment marketed for fat loss whose largest human trial failed and was abandoned.