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.
The short version
What it does
Raises your own growth hormone, and reliably makes you hungrier. Sold as a capsule for muscle and recovery.
How it does it
Presses the same button as ipamorelin, on the gland that releases growth hormone. The difference is that this one survives your stomach, so you can swallow it.
The catch
Human trials found it raised growth hormone and also made insulin work less well, pushing blood sugar up. That is a large part of why it was never approved, and it is not what the shops mention.
Everything below goes into the detail, with sources.
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.
At a glance
- Compound type
- Small molecule. Not a peptide.
- Also called
- Ibutamoren, ibutamoren mesylate
- Drug class
- Growth hormone secretagogue, orally active
- Route
- Swallowed, capsule or liquid
- Human trials
- Multiple, including in older adults. Never approved.
- Key trial finding
- Raised GH and IGF-1, and reduced insulin sensitivity
- UK status
- Unlicensed medicine. Supply for human use prohibited.
- In sport
- Named as ibutamoren under WADA S2.2.4. Prohibited at all times.
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.
02How it came about
MK-677 was developed by a major pharmaceutical company in the 1990s as an orally active growth hormone secretagogue, aimed at conditions involving muscle wasting and frailty in older people. Unlike the peptides in its class, it survives digestion, which made a daily tablet possible.
It was studied reasonably extensively in humans. It was not approved, and the glucose findings are a substantial part of why.
03UK 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.
04How 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.
05What it is not
Claims that attach themselves to this compound and do not hold up.
- Not a peptide. A small molecule, despite being shelved with peptides everywhere it is sold.
- Not a SARM. SARMs act on androgen receptors. This acts on the ghrelin receptor. The two have nothing in common beyond being sold by the same shops.
- Not a lawful supplement. Frequently sold as one. It is neither a licensed medicine nor a permitted food supplement ingredient in the UK.
- Not without a metabolic cost. Reduced insulin sensitivity and raised blood glucose showed up in the trials themselves.
06What 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.
07Reported 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.
08Interactions and cautions
The glucose effect is the one that matters. Anyone with diabetes, prediabetes or metabolic risk is taking something that human trials showed worsens insulin sensitivity. There is no SPC, so no formal interaction list, and no prescriber is positioned to manage it.
09Stopping
Growth hormone and IGF-1 fall back. Appetite stimulation stops. Lean mass gains attributable to fluid retention resolve, which accounts for part of what people report losing.
10Monitoring
Nothing formal. If anyone were monitoring sensibly, fasting glucose and HbA1c would be the priority given the trial findings, which is not what the marketing focuses on.
11Questions worth asking
Take these to a doctor or pharmacist. A good clinician will not mind being asked, and the answers are specific to you in a way nothing on this page can be.
- Do I understand this reduced insulin sensitivity in human trials?
- Do I have any existing metabolic risk that makes that a bad trade?
- Am I clear this is not a peptide and not a SARM, whatever the shop said?
12Common questions
Is MK-677 a SARM?
No. SARMs are selective androgen receptor modulators. MK-677 acts on the growth hormone secretagogue receptor, the ghrelin receptor. It is sold alongside SARMs, which is where the confusion comes from.
Does MK-677 work?
It reliably raises growth hormone and IGF-1, and some studies reported increases in lean body mass. Whether that is a benefit is a different question, since part of the gain is fluid retention and the trials also showed worsened insulin sensitivity.
Why was it never approved?
Raising a hormone and increasing lean mass on a scan is not what a regulator needs to see. It needs improved function or outcomes, weighed against harms. The glucose findings were a real problem, and approval did not follow.
Is it legal in the UK?
It has no marketing authorisation, so supplying it for human use is prohibited. It is not a controlled drug. Selling it as a dietary supplement does not make it one.
13Sources
Links go to the authoritative source. Where a document sits behind a paywall or moves around, the full 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
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