The MK-677 study most people cite found more fat-free mass after a year, but no improvement in strength or everyday physical function. Fat-free mass means everything in the body except fat, including water. The same trial found higher blood sugar and a weaker response to insulin, the hormone that helps control it.
What question did the MK-677 study ask?
Ralf Nass and colleagues at the University of Virginia asked whether stimulating the body's growth-hormone release could change aging-related tissue loss. Their study appeared in Annals of Internal Medicine in 2008.
MK-677, also called ibutamoren, activates the ghrelin receptor, a cell switch involved in hunger and growth-hormone release. That makes it an agonist, meaning something that activates a receptor. It signals the pituitary, a small gland beneath the brain, rather than supplying growth hormone. The ghrelin discovery story explains that pathway.
The earlier Rudman growth-hormone study tested the hormone itself. Its findings cannot stand in for an ibutamoren trial.
Who took part, and for how long?
The full Nass paper reports 71 people randomized, with 65 completing the first year: 43 receiving MK-677 and 22 receiving placebo, an inactive comparison. The first-year group was aged 60–81.
Participants were generally healthy. Exclusions included diabetes, smoking, untreated high blood pressure, a body mass index of 35 or more, and any history of cancer other than some skin cancers. This wasn't a trial in young athletes or people recovering from injury.
The study used 25 mg by mouth daily. That was the trial protocol; a prescriber sets any individual dose. Participants and staff remained unaware of treatment assignments throughout both years. In year two, some participants switched treatments; 53 completed two years. The registry record, NCT00474279, also describes this blinded design.
What changed after 12 months?
Fat-free mass rose 1.1 kilograms with MK-677 and fell 0.5 kilograms with placebo. The paper identified fat-free mass and deep abdominal fat as its two main outcomes. Researchers used body-composition measurements and scans to distinguish them.
| One-year change | MK-677 | Placebo |
|---|---|---|
| Fat-free mass | +1.1 kg | −0.5 kg |
| Lean tissue in arms and legs | +0.5 kg | −0.3 kg |
| Body weight | +2.7 kg | +0.8 kg |
Deep abdominal fat and total fat did not differ significantly between groups. Strength, walking, stair climbing, chair rises and quality of life did not improve either.
Growth hormone and IGF-1, a growth signal made largely by the liver in response to growth hormone, increased. About half the treated group reached the young-adult IGF-1 range. That isn't a personal treatment target; IGF-1 levels by age explains why.
MK-677 is coming soon to Promise as a compounded medication, prepared by a pharmacy for an individual prescription. That is different from an FDA-approved product: the formulation Promise will offer is not FDA-approved.
Side effects in the 2008 trial
About two in three treated participants reported increased appetite. These are the paper's own counts from 65 people, not rates that apply to everyone.
| Finding | MK-677, n=43 | Placebo, n=22 |
|---|---|---|
| Increased appetite | 29/43 (67%) | 8/22 (36%) |
| Mild, temporary leg swelling | 19/43 (44%) | 6/22 (27%) |
| Temporary muscle pain | 14/43 (33%) | 2/22 (9%) |
| Joint pain | 25/43 (58%) | 17/22 (77%) |
| Average fasting glucose change | +5 mg/dL | −1 mg/dL |
Only the appetite difference among those four symptoms met the study's threshold for statistical significance. Insulin sensitivity, meaning how readily the body responds to insulin, also fell with MK-677. The average hides a spread: fasting glucose moved from below 100 into the 101–110 mg/dL range in 16 people on MK-677 and 2 on placebo, and reached 125–126 mg/dL in two others on MK-677. In four participants the dose was lowered to 10 mg without unblinding, two of them because of rising fasting glucose.
The paper recorded a heart attack and tongue cancer during MK-677 treatment, and kidney cancer on placebo. Another participant was diagnosed with colon cancer at the end of year two; she had taken MK-677 in year one and placebo in year two. Those events alone don't establish causation. The paper did not report a heart-failure event, but the trial's registry record shows that people with congestive heart failure or coronary artery disease could not enroll, so it could not test that risk.
What criticism and hip-fracture trials add
The authors acknowledged that their trial was too small and short to settle functional benefits. Marc Blackman's accompanying editorial was titled “Use of growth hormone secretagogues to prevent or treat the effects of aging: not yet ready for prime time.”
In May 2009, the journal published letters by Rafael, Gaugg and Webster, with an author reply.
Bach's 2004 trial in Journal of the American Geriatrics Society enrolled 161 hip-fracture patients. Over six months, IGF-1 rose 84% with MK-0677, another name for ibutamoren, versus 17% with placebo. Functional improvements did not differ significantly.
Adunsky's 2011 trial in Archives of Gerontology and Geriatrics assigned 62 patients to ibutamoren and 61 to placebo. A walking-speed score favored treatment, but most other functional measures did not. The trial stopped early because of a congestive-heart-failure safety signal in a limited number of patients (concern that the heart wasn't pumping well enough, causing fluid buildup), and the authors concluded that MK-677 has an unfavorable safety profile in this patient population. FDA cites this trial when it describes ibutamoren's heart-failure risk.
What newer research is asking
As of October 29, 2026, the day this article was written, a trial first posted August 10, 2026 plans to compare LUM-201 plus semaglutide with semaglutide plus placebo. LUM-201 is ibutamoren. The planned 202 participants are older adults with obesity and mild physical limitations; the main outcome concerns physical performance after 26 weeks. It isn't recruiting yet and has no results.
An August 11, 2026 sports-medicine review also found that current human trials don't substantiate claimed recovery or performance benefits. It covered six compounds sold for sports recovery, MK-677 among them, and named congestive heart failure among MK-677's documented risks; it summarizes older studies rather than adding a new trial.
Where the muscle-building claim goes too far
Online, this trial is often summed up as proof that MK-677 is growth hormone in a pill that builds muscle. Calling ibutamoren swallowed growth hormone gets the mechanism wrong. Calling a rise in fat-free mass proof of stronger muscles gets the outcome wrong. Water contributes to that measurement, and the trial separately tested strength without finding improvement.
Sermorelin is another signal for growth-hormone release, with its own evidence. The MK-677 and sermorelin comparison covers their differences. Compounded sermorelin is different from an FDA-approved sermorelin product once marketed as Geref, which has since been discontinued; today's compounded formulation is not FDA-approved (FDA's historical notice).
Current FDA and sport status
MK-677 is not FDA-approved (FDA's ibutamoren statement). FDA's compounding safety summary, marked current April 22, 2026, includes ibutamoren mesylate for both 503A and 503B compounding and says it “poses significant safety risks due to the potential for congestive heart failure in certain patients,” citing the hip-fracture trial that ended early.
As of October 29, 2026, the day this article was written, ibutamoren isn't among the six substances in HHS's October 28 draft policy. The HHS policy explainer covers that separate development.
WADA's published 2027 list, effective January 1, 2027, names ibutamoren among growth-hormone secretagogues, substances that prompt hormone release. It remains prohibited both during and outside competition.
Promise also offers CJC-1295/ipamorelin by prescription. CJC-1295 mimics growth-hormone-releasing hormone, while ipamorelin acts on the same ghrelin receptor as MK-677; the Nass trial tested neither peptide, the blend, nor any compounded formulation. CJC-1295 and ipamorelin are not FDA-approved; the compounded blend is not FDA-approved.
What belongs in the prescribing conversation
A licensed provider may still prescribe — that decision is between you and your doctor. At Promise, a licensed provider reviews every request, and not everyone qualifies.
The useful discussion concerns the intended goal, glucose control, swelling and heart history, alongside what will be monitored. Any prescribed compounded medication is dispensed by a licensed U.S. compounding pharmacy. A result from Merck's trial medication cannot establish the safety or effects of another preparation.
