MK-677 (ibutamoren): evidence, FDA status and research

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, 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, a compound that makes the pituitary release growth hormone. Development stopped after mixed trial results, and the compound later passed through Lumos Pharma for a pediatric growth hormone deficiency program that also ended. ⁴⁵

It has never been approved anywhere. The FDA lists ibutamoren mesylate in Category 2 of substances nominated for compounding, the category for substances with significant safety risks, and its advisory committee discussed it in October 2024. Despite that, it is widely sold online. ¹

How it works

MK-677 mimics ghrelin, the stomach hormone that signals hunger and also triggers growth hormone release. It binds the ghrelin receptor (GHS-R1a) in the pituitary and hypothalamus, which increases the size of growth hormone pulses; the liver responds by making more IGF-1. Because it is a ghrelin mimic, it also increases appetite. The growth hormone rise feeds back through normal regulation, so levels stay within the physiological range and do not reach the levels seen with injected growth hormone. ⁵

What human research shows

A two-year randomized, double-blind, placebo-controlled trial in 65 healthy adults aged 60 to 81 found that 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, body weight rose 2.7 kg, and there was no improvement in strength, function, or quality of life. Fasting glucose rose and insulin sensitivity fell. ⁵

A 12-month randomized trial in 563 patients with mild to moderate Alzheimer's disease tested the hypothesis that raising IGF-1 would slow decline. IGF-1 rose by 60 to 73 percent, confirming the drug worked on its target, but there was no difference from placebo on any cognitive or functional 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), transient mild leg swelling, and muscle pain. The metabolic findings are the main concern: fasting glucose rose and insulin sensitivity decreased, which matters for anyone at risk of diabetes. The 563-patient Alzheimer's trial found it generally tolerated over a year. ⁴⁵

The FDA's Category 2 designation reflects the lack of long-term safety data and the metabolic signal. Effects of years of use in young healthy people, the actual customer base, have not been studied, and 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. It is taken 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 compared with a small loss on placebo, with no gain in strength. No trial has studied young people or athletes. ⁵

Has it won FDA approval?

No. It was studied by Merck and later Lumos Pharma and never submitted 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, muscle aches, and higher fasting blood sugar with reduced insulin sensitivity. 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, and 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