All peptides / Muscle and bone
MK-677 (ibutamoren)
Non-peptide ghrelin mimetic
Also Ibutamoren, MK-677, MK677, MK 677, Ibutamoren mesylate, Nutrobal
- Evidence
- BSome human evidence
- FDA status
- Not approvedas of 2026-10-26
- Route
- Oral
- Studies cited
- 2 human0 animal or cell
A pill sold to bodybuilders to raise growth hormone for muscle and sleep. It does raise the hormone, but the muscle gain was small and blood sugar went up.
Sold for
MK-677 is sold in the bodybuilding market as an oral growth hormone booster that builds muscle, deepens sleep, and heals injuries without injections.
Studies say
Controlled trials confirm it raises growth hormone and IGF-1, but the body composition change in 65 older adults was small, strength did not improve, blood sugar rose, and a 563-patient Alzheimer's trial failed, so the evidence is grade B.
Why grade B. Two randomized placebo-controlled trials are cited: a two-year trial in 65 healthy older adults that raised growth hormone and IGF-1 and increased fat-free mass, and a 563-patient trial in Alzheimer's disease that raised IGF-1 but did not slow decline. Those are real controlled human data, which is B, but the muscle-building use it is sold for has only the 65-person trial, with modest body composition changes and no strength or function benefit. 45
FDA. Not approved by the FDA for any use. MK-677 (ibutamoren) is an investigational compound that Merck and later Lumos Pharma studied but never submitted for approval. The FDA placed ibutamoren mesylate in Category 2 of its compounding bulk-substances list, meaning significant safety risks, and reviewed it at a Pharmacy Compounding Advisory Committee meeting in October 2024. It is sold online as a research chemical. 1
Written from 5 cited sources. Last refreshed 2026-10-27. Not physician reviewed.
What this means for you
- What people take it for
- Muscle gain, sleep and anti-ageing
- Can a US doctor prescribe it?
- No. It is not approved and is sold as a research chemical.
- Properly tested in people?
- Partly: two controlled trials, of 65 and 563 people, with small or no real benefit.
Evidence checklist
- Randomised controlled trial Two placebo-controlled trialsyes
- Human study over 100 people 563 patients in the Alzheimer's trialyes
- More than one research group Merck-linked trials onlyno
- Clinical outcomes, not surrogate markers Mostly IGF-1 and body compositionno
- Human safety data beyond case reports Glucose rise seen in controlled trialsyes
Drawn from the cited studies below. A dash means the sources give no information.
What it is
MK-677, or ibutamoren mesylate, is a small-molecule drug taken by mouth. It is not a peptide, though it is sold alongside peptides because of what it does. Merck developed it in the 1990s as a growth hormone secretagogue. That is a compound that makes the pituitary release growth hormone. Development stopped after mixed trial results. The compound later passed through Lumos Pharma for a pediatric growth hormone deficiency program, which also ended. 45
It has never been approved anywhere. The FDA lists ibutamoren mesylate in Category 2 of substances nominated for compounding. That category is for substances with significant safety risks. The FDA's advisory committee discussed it in October 2024. Even so, it is widely sold online. 1
How it works
MK-677 mimics ghrelin, the stomach hormone that signals hunger. Ghrelin also triggers growth hormone release. It binds the ghrelin receptor (GHS-R1a) in the pituitary and hypothalamus. This makes growth hormone pulses larger, and the liver makes more IGF-1. Because it mimics ghrelin, it also increases appetite. The growth hormone rise feeds back through normal regulation. So levels stay in the normal range. They do not reach the levels seen with injected growth hormone. 5
What human research shows
A two-year randomized, double-blind, placebo-controlled trial enrolled 65 healthy adults aged 60 to 81. Daily MK-677 raised growth hormone and IGF-1 to young-adult levels. Fat-free mass rose by 1.1 kg, versus a 0.5 kg fall on placebo. But visceral fat and total fat did not change. Limb fat increased more, and body weight rose 2.7 kg. Strength, function and quality of life did not improve. Fasting glucose rose and insulin sensitivity fell. 5
A 12-month randomized trial enrolled 563 patients with mild to moderate Alzheimer's disease. It tested the idea that raising IGF-1 would slow decline. IGF-1 rose by 60 to 73 percent, so the drug did work on its target. But it made no difference from placebo on any thinking or daily-function measure. 4
| Study | Model | Finding |
|---|---|---|
| MK-677 in healthy older adults (Nass 2008) | Humans, n=65 aged 60 to 81, randomized double-blind placebo-controlled, 2 years | GH and IGF-1 rose to young-adult levels; fat-free mass up 1.1 kg versus down 0.5 kg; no strength or function gain; glucose and insulin resistance rose. 5 |
| MK-677 in Alzheimer's disease (Sevigny 2008) | Humans, n=563 with mild to moderate AD, randomized double-blind placebo-controlled, 12 months | IGF-1 rose 60 to 73 percent but cognition and function did not differ from placebo. 4 |
| FDA 503A bulk substances list | Regulatory listing | Ibutamoren mesylate placed in Category 2 for significant safety risks. 1 |
Safety
In the older-adult trial, the common side effects were increased appetite (which faded over months), brief mild leg swelling and muscle pain. The main concern is the metabolic findings. Fasting glucose rose and insulin sensitivity decreased. That matters for anyone at risk of diabetes. The 563-patient Alzheimer's trial found the drug generally tolerated over a year. 45
The FDA's Category 2 designation reflects the lack of long-term safety data and the metabolic signal. No one has studied years of use in young healthy people, who are the actual customer base. Online products have no quality assurance. 15
Questions for your clinician
- Is there evidence MK-677 improves strength or recovery, not just lean mass?
- How could it affect my blood sugar and diabetes risk?
- Why did the Alzheimer's trial show no clinical benefit?
Questions people ask
Is MK-677 a peptide?
No. It is a small-molecule drug that mimics the peptide hormone ghrelin. People take it by mouth, which is part of its appeal over injected secretagogues. 5
Does MK-677 build muscle?
In the only relevant trial, 65 older adults gained about 1.1 kg of fat-free mass over a year. Those on placebo lost a little. Strength did not improve. No trial has studied young people or athletes. 5
Has it won FDA approval?
No. Merck and later Lumos Pharma studied it, and no one ever submitted it for approval. The FDA has flagged it as a significant safety risk for compounding. 1
What unwanted effects does it cause?
Increased appetite, water retention and muscle aches. Fasting blood sugar goes up and insulin sensitivity goes down. Long-term effects in healthy young users are unknown. 5
Why did the Alzheimer's trial matter?
It showed the drug reliably raises IGF-1 in people over a year. It also showed that doing so did not change the course of the disease. It is the largest controlled dataset on MK-677. 4
Citations
- FDA: Bulk drug substances nominated for use in compounding under section 503A, category list fda.gov
- Nass 2008, Ann Intern Med: Effects of an oral ghrelin mimetic on body composition in healthy older adults (DOI) doi.org
- Sevigny 2008, Neurology: MK-677 no clinical effect on AD progression (DOI) doi.org
- Sevigny 2008, Neurology: Growth hormone secretagogue MK-677, no clinical effect on AD progression pubmed.ncbi.nlm.nih.gov
- Nass 2008, Ann Intern Med: Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults pubmed.ncbi.nlm.nih.gov