MK-677
Growth hormone secretagogue, non-peptide · Ibutamoren, ibutamoren mesylate, sometimes sold as Nutrobal
- UK status
- Unlicensed medicine
- Availability
- Research use only
- Evidence base
- Human trials exist, no approval
- Controlled drug
- No, but WADA prohibited
Sequence
Not a peptide. A small molecule, so there is no amino acid sequence.
MK-677 gets grouped with peptides because it does the same thing as several of them. It is not one. It is a small molecule that can be swallowed, which is precisely why it is so widely sold.
01What it is
MK-677, also called ibutamoren, is a non-peptide compound that activates the same receptor as ipamorelin: the growth hormone secretagogue receptor, otherwise the ghrelin receptor. Being a small molecule rather than a peptide, it survives digestion and works as a capsule or liquid.
It is not a peptide, despite where it is usually shelved. And it is not a SARM, despite being sold alongside them: SARMs act on androgen receptors and have nothing to do with growth hormone. Both errors are extremely common in product listings, which is itself a reason to distrust the listing.
02UK legal and licensing status
MK-677 has no marketing authorisation in the UK or anywhere else. Supplying it for human use without one is unlawful under the Human Medicines Regulations 2012. It is not a controlled drug under the Misuse of Drugs Act.
Because it is oral, it is frequently sold as a dietary supplement or a research chemical. It is neither a licensed medicine nor a lawful food supplement ingredient in the UK, and selling it as the latter does not change what it is.
Athletes: WADA names ibutamoren explicitly under S2.2.4, among growth hormone secretagogues and their mimetics. Prohibited at all times. It has appeared in contaminated supplement cases, which for a tested athlete is a strict liability problem regardless of intent.
03How it works
It activates the ghrelin receptor, increasing growth hormone and subsequently IGF-1. Effects are sustained rather than pulsatile because of its long duration of action, and appetite stimulation is a well-recognised consequence of activating that receptor.
04What the evidence shows
MK-677 has been studied in humans more than most compounds in this register, including in older adults and in trials examining muscle mass and bone. It reliably raises growth hormone and IGF-1, and some studies reported increases in lean body mass.
Raising a hormone and increasing lean mass on a scan is not the same as making people healthier or more functional, which is what a regulator needs to see. Trials also raised concerns about glucose metabolism, including reduced insulin sensitivity and raised blood glucose. It was not approved for any indication, and lean mass gains reported in trials included fluid retention.
So the honest summary is that it does something measurable, the something is not clearly a benefit, and it comes with a metabolic cost that showed up in the trials themselves.
No long-term safety programme was completed. The glucose and insulin sensitivity findings are the specific concern, particularly for anyone with existing metabolic risk, and sustained IGF-1 elevation over years in healthy adults is uncharacterised.
05Reported harms
Effects reported in human studies include increased appetite, fluid retention, joint pain, lethargy, and raised blood glucose with reduced insulin sensitivity. There is no SPC and therefore no authoritative frequency table.
Because it is often sold as a supplement rather than a research chemical, product quality varies widely and mislabelling is common. Contaminated supplement cases have been documented.
06Sources
Links go to the primary source. Where a source is behind a paywall or requires registration, the citation is given so you can find it yourself.
- Prohibited List, S2.2.4 ibutamorenWADA
- MK-677 human trials in older adultsPubMed
- Unlicensed medicines guidanceMHRA
- Bulk drug substances reviewFDA
07Change history
Every substantive change to this record is logged here with its date. Corrections are made openly, not quietly.
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