Peptide Evidence Index

MK-677 (Ibutamoren)

Evidence last reviewed: September 2026

Quick answers

What is it?: MK-677 (ibutamoren) is a synthetic, orally active small molecule — not a peptide — designed by Merck to mimic ghrelin and trigger growth hormone release. It has never been approved as a medicine for any purpose.
Why are people interested in it?: It has the deepest human trial record of any compound in this library, tested in older adults, Alzheimer's disease, fibromyalgia, and kidney disease, so people want to know what that large body of research actually found.
What has actually been studied?: A 2-year, placebo-controlled trial in 65 healthy older adults measured growth hormone, IGF-1, lean mass, strength, and blood sugar; a Phase 2 trial tested it in 512 Alzheimer's patients; other trials covered fibromyalgia, kidney dialysis, hip fracture, and fatty liver disease.
How strong is the evidence?: Genuinely mixed: it reliably raises growth hormone and IGF-1 and increased lean mass in the best-run trial, but that same trial found no improvement in strength or function and a real rise in blood sugar; the Alzheimer's and fibromyalgia trials appear never to have been published.
What don't we know yet?: Whether the metabolic trade-offs seen in older adults are worse, similar, or absent in younger users, what the unpublished Alzheimer's and fibromyalgia trials found, and whether it has any effect on strength or performance in younger people — this hasn't been tested.
Where can I read the original research?: Sources at the bottom of this page: Chapman et al., Journal of Clinical Endocrinology & Metabolism 1996; Nass et al., Annals of Internal Medicine 2008.

Plain-English overview

MK-677, known generically as ibutamoren, differs from most compounds in this library because it isn't a peptide at all — it's a small synthetic molecule developed by Merck to mimic the hunger hormone ghrelin and trigger growth hormone release from the pituitary gland, taken as a pill rather than injected. It has never been approved as a medicine for any purpose. It also has the deepest human trial record of any compound covered here, tested in randomized trials spanning healthy older adults, Alzheimer's disease, fibromyalgia, and kidney disease. That breadth is real, but the findings are genuinely mixed: the clearest data, from a well-run two-year trial in older adults, show it reliably raises growth hormone and IGF-1 and increases lean mass, but the same trial found no corresponding gain in strength or physical function, plus a real rise in blood sugar. Its two disease-outcome trials in Alzheimer's disease and fibromyalgia both completed years ago but appear never to have posted results or been published.

What researchers are studying it for

body composition and physical function in healthy older adults
Alzheimer's disease (cognitive decline)
fibromyalgia
chronic kidney disease / dialysis nutritional status
hip fracture recovery
nonalcoholic fatty liver disease
pediatric growth hormone deficiency (ongoing Phase 3, related oral formulation)

Current evidence level

Mixed human evidence

Regulatory status: Not an approved medicine. Evidence strength and approval are scored separately; approval is a regulatory decision about a specific use, not a measure of how much research exists.

Human research

MK-677 has been tested in more human trials, across more conditions, than any other compound in this library. An early dose-ranging trial gave 32 healthy older adults (64–81 years) placebo or 2, 10, or 25 mg of MK-677 daily for up to 28 days; the 25 mg dose increased mean 24-hour growth hormone concentration by 97% and raised IGF-I into the normal range for young adults, but also raised fasting glucose significantly (Chapman et al., Journal of Clinical Endocrinology & Metabolism, 1996). The clearest and longest data come from a two-year, randomized, placebo-controlled trial in 65 healthy older adults: daily MK-677 reliably raised growth hormone and IGF-1 and increased fat-free (lean) mass compared with placebo, but found no corresponding improvement in muscle strength or physical function, and it raised fasting blood sugar, reduced insulin sensitivity, and raised cortisol — real, measured trade-offs (Nass et al., Annals of Internal Medicine, 2008). Eight trials in total are registered on ClinicalTrials.gov. The largest, a Phase 2 trial in 512 patients with Alzheimer's disease sponsored by Merck (NCT00074529), tested whether MK-677 could slow cognitive decline over a year; it is marked complete, but no results have ever been posted and no published paper describing its findings could be located. A 64-patient fibromyalgia trial (NCT00116129) is in the same position — completed, but with no posted or published results. Other completed trials include a 49-patient trial in kidney dialysis patients with posted results (NCT00395291), a 12-patient pilot in fatty liver disease with posted results (NCT05364684, testing the related oral formulation LUM-201), and an 83-patient hip fracture recovery trial that was terminated early (NCT00128115). A separate ongoing Phase 3 trial of LUM-201 is recruiting children with growth hormone deficiency (NCT06948214). None of the eight trials tested MK-677 for muscle building, fat loss, or anti-aging in healthy younger adults, the population it is most heavily marketed to today.

Animal and preclinical research

Not covered in the published research we reviewed for this page — the source material for MK-677 describes only human trials and registry records, with no animal or preclinical data included.

Major findings

In a 28-day dose-ranging trial in 32 older adults, 25 mg/day MK-677 raised mean 24-hour growth hormone by 97% and brought IGF-I into the normal young-adult range, while also significantly raising fasting glucose (Chapman et al., 1996).
A 2-year, placebo-controlled trial in 65 healthy older adults found MK-677 reliably raised growth hormone and IGF-1 and increased lean mass, but produced no improvement in strength or physical function, plus a real rise in blood sugar and a drop in insulin sensitivity (Nass et al., 2008).
A 512-patient Phase 2 Alzheimer's disease trial and a 64-patient fibromyalgia trial both completed years ago, but neither has ever posted results or been published.
An 83-patient hip fracture recovery trial was terminated early, and its results were never posted.
A related oral formulation (LUM-201) is the only MK-677-family compound in an active, approval-track Phase 3 trial, for pediatric growth hormone deficiency.
No trial has tested MK-677 in the healthy younger adults who are its main current market, for muscle building, fat loss, or anti-aging.

What has not been established

Whether the metabolic trade-offs seen in older adults (higher blood sugar, lower insulin sensitivity) are worse, similar, or absent in younger, healthy users.
What the Alzheimer's and fibromyalgia trials actually found, since neither appears to have been published.
Whether raising growth hormone this way has any effect on strength or athletic performance in younger people — this hasn't been tested.
What years of continuous daily use does — the longest published trial ran two years, in older adults, not younger ones.
Whether it affects long-term cancer risk, given growth hormone's role in cell growth signaling.

Important limitations

The two published trials with usable outcome data were both conducted in adults over 60, not the younger population that buys MK-677 today.
Two of the largest disease-outcome trials (Alzheimer's, fibromyalgia) completed years ago with no posted or published results, so their actual findings are unknown.
The best trial's positive result (lean mass) did not translate into a functional benefit (strength), showing that a biological change doesn't guarantee a meaningful outcome.
No dose-by-dose findings were reported publicly for any of the disease-specific trials, so it isn't possible to say which dose, if any, was more effective.
How today's ibutamoren products compare in purity and consistency to the pharmaceutical-grade material used in trials is unknown.

Regulatory status

MK-677/ibutamoren has never received regulatory approval for any indication, in the United States or elsewhere. A related, company-developed oral formulation (LUM-201) is in an ongoing Phase 3 trial for pediatric growth hormone deficiency, the only development track in this group aimed at formal drug approval.

Primary research sources

Chapman IM, et al., "Stimulation of the growth hormone (GH)-insulin-like growth factor I axis by daily oral administration of a GH secretagogue (MK-677) in healthy elderly subjects": Journal of Clinical Endocrinology & Metabolism 1996; PMID 8954023, DOI 10.1210/jcem.81.12.8954023
Nass R, et al., "Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults: a randomized trial": Annals of Internal Medicine 2008; PMID 18981485, DOI 10.7326/0003-4819-149-9-200811040-00003
"MK-0677 in the treatment of Alzheimer's disease": ClinicalTrials.gov NCT00074529, n=512, Phase 2, Merck, completed 2006, no results posted
"MK-0677 in the treatment of primary fibromyalgia": ClinicalTrials.gov NCT00116129, n=64, Phase 2, completed 2008, no results posted
"MK-0677 effect on IGF-1 levels in ESRD patients": ClinicalTrials.gov NCT00395291, n=49, University of Virginia / Merck, completed 2010, results posted
"The impact of ibutamoren (LUM-201) on nonalcoholic fatty liver disease": ClinicalTrials.gov NCT05364684, n=12, pilot, completed 2024, results posted
"MK-0677 in sarcopenia after hip fracture": ClinicalTrials.gov NCT00128115, n=83, Merck, terminated 2007, no results posted
"Phase 3 study of LUM-201 in children with growth hormone deficiency": ClinicalTrials.gov NCT06948214, n=150, Lumos Pharma, recruiting, ongoing

Full evidence entry (complete data, registry records, dosing evidence)

Mixed human evidence

Controlled human trials exist and disagree

At a glance

Also known as: Ibutamoren mesylate, Ibutamoren, L-163, 191
Class: Synthetic, orally active non-peptide growth hormone secretagogue
Derived from: Not derived from a natural hormone fragment — a small-molecule drug candidate designed by Merck to mimic ghrelin's action on the growth-hormone-secretagogue receptor, taken as a pill rather than injected
Registered human trials: 8
…with published results: 2
Largest human trial: 512 patients with Alzheimer's disease (Phase 2, Merck, completed 2006), testing cognitive function over 12 months. Completed, but no results have been posted on the registry, and no published outcome paper could be located this session.
Studied for: body composition and physical function in healthy older adults, Alzheimer's disease (cognitive decline), fibromyalgia, chronic kidney disease / dialysis nutritional status, hip fracture recovery, nonalcoholic fatty liver disease, pediatric growth hormone deficiency (ongoing Phase 3)
Dosing evidence: Doses used in trialsMultiple real controlled trials, including a published 2-year randomized trial in 65 older adults, used a fixed daily oral dose and measured concrete outcomes — but that trial found no gain in strength or physical function despite raising growth hormone, alongside a real rise in blood sugar.
Regulatory status: Not approved as a medicine anywhere. MK-677/ibutamoren has never received regulatory approval for any indication, though a related, company-developed oral formulation is in an ongoing Phase 3 trial for pediatric growth hormone deficiency.

What it is

MK-677 — known generically as ibutamoren — differs from most other compounds in this library in one important way: it is not a peptide at all. It's a small synthetic molecule, developed by Merck, designed to mimic the action of ghrelin (the body's natural "hunger hormone") on the same receptor, triggering the pituitary gland to release growth hormone. Because it isn't a peptide, it survives digestion and is taken as a pill, unlike the injectable compounds in this library.

It has never been approved as a medicine for any purpose.

What the studies actually found

MK-677 has been tested in more human trials, across more conditions, than any other compound covered in this library — in healthy older adults, Alzheimer's disease, fibromyalgia, kidney disease, and after hip fracture. That breadth is real. What it found is genuinely mixed.

The clearest published data come from a well-run, two-year, placebo-controlled trial in 65 healthy older adults. Daily treatment reliably raised growth hormone and IGF-1 back into the range seen in young adults, and increased fat-free (lean) mass compared with placebo. But the same trial found no corresponding improvement in muscle strength or physical function — the extra lean mass didn't translate into people being measurably stronger or more capable. It also raised fasting blood sugar and reduced insulin sensitivity, and raised cortisol, a stress hormone — real, measured trade-offs, not a hypothetical concern. Common side effects included increased appetite and mild swelling.

An earlier, shorter dose-ranging study in elderly volunteers found the same hormone-raising pattern along with a rise in blood sugar after just a few weeks — a consistent finding across separate research groups, not a one-off.

Beyond hormone and body-composition effects, MK-677 has been tested as a potential treatment in Alzheimer's disease and fibromyalgia — both real, disease-outcome trials, not just safety studies — but neither trial's findings could be located, in the registry or in the published literature, despite both trials having completed years ago.

What exists in humans

Eight trials are registered on ClinicalTrials.gov. The largest, a Phase 2 trial in 512 patients with Alzheimer's disease sponsored by Merck, tested whether MK-677 could slow cognitive decline over a year; it's marked complete, but no results have ever been posted, and no published paper describing what it found could be located.

Other completed trials include a 64-patient trial in fibromyalgia (also no posted or published results), a 49-patient trial in kidney dialysis patients (results posted), a 12-patient pilot in fatty liver disease (results posted), and an 83-patient hip fracture recovery trial that was terminated early.

A separate oral formulation of the same molecule, developed by a different company under the name LUM-201, is currently in an ongoing, recruiting Phase 3 trial for growth hormone deficiency in children — the only trial in this group aiming at formal drug approval.

None of the eight trials tested MK-677 for muscle building, fat loss, or anti-aging in healthy younger adults — the population it is most heavily marketed to today.

What doses have been studied in humans

The most informative trial gave healthy adults over 60 a single fixed daily oral dose for up to two years, tracking hormone levels, body composition, strength, and blood chemistry throughout — real efficacy-level dosing evidence, in a real population, over real time. An earlier, shorter trial tested several different daily oral dose levels against each other and against placebo over a few weeks, in a similar older population.

None of the disease-specific trials (Alzheimer's, fibromyalgia, kidney disease, hip fracture, fatty liver) that tested MK-677 in humans reported dose-by-dose findings publicly, so it isn't possible to say which, if any, dose was more effective for those conditions.

No trial has tested MK-677 in the population most likely to buy it today — healthy adults in their 20s to 40s seeking muscle gain or fat loss — so no dose has been validated for that use, at any duration.

What remains unknown

Whether the metabolic trade-offs seen in older adults (higher blood sugar, lower insulin sensitivity) are worse, similar, or absent in younger, healthy users
What the Alzheimer's and fibromyalgia trials actually found, since neither appears to have been published
Whether raising growth hormone this way has any effect on strength or athletic performance in younger people — this hasn't been tested
What years of continuous daily use does — the longest published trial ran two years, in older adults, not younger ones
Whether it affects long-term cancer risk, given growth hormone's role in cell growth signaling
How today's ibutamoren products compare in purity and consistency to what was used in the actual trials

Registry and study records

Stimulation of the GH-IGF-I axis by daily oral administration of MK-677 in healthy elderly subjects: PubMed · DOI: 10.1210/jcem.81.12.8954023 — randomized, double-blind, placebo-controlled dose-ranging trial, n=32
Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults: PubMed · DOI: 10.7326/0003-4819-149-9-200811040-00003 — 2-year randomized controlled trial, n=65, Annals of Internal Medicine, 2008
MK-0677 in the treatment of Alzheimer's disease: ClinicalTrials.gov NCT00074529 · n=512, Phase 2, Merck, completed 2006, no results posted, no published paper located
MK-0677 in the treatment of primary fibromyalgia: ClinicalTrials.gov NCT00116129 · n=64, Phase 2, completed 2008, no results posted, no published paper located
MK-0677 effect on IGF-1 levels in ESRD patients: ClinicalTrials.gov NCT00395291 · n=49, University of Virginia / Merck, completed 2010, results posted
The impact of ibutamoren (LUM-201) on nonalcoholic fatty liver disease: ClinicalTrials.gov NCT05364684 · n=12, pilot, completed 2024, results posted
MK-0677 in sarcopenia after hip fracture: ClinicalTrials.gov NCT00128115 · n=83, Merck, TERMINATED 2007, no results posted
Phase 3 study of LUM-201 in children with growth hormone deficiency: ClinicalTrials.gov NCT06948214 · n=150, Lumos Pharma, recruiting, ongoing

See the full Evidence Index →

Evidence last reviewed: September 2026. Peptide Proof reports what studies found. We do not give medical advice, dosing guidance, or treatment recommendations.