MK-677, also called ibutamoren, is a compound that stimulates your body’s production of growth hormone by mimicking a hunger hormone called ghrelin. It is not a steroid or an injectable. It’s taken orally, and it works by activating the same receptor that ghrelin uses, triggering the pituitary gland to release growth hormone in natural pulses. MK-677 is not approved by any government health authority for human therapeutic use, but it has been studied in clinical trials for its effects on body composition, bone density, sleep, and aging.
How MK-677 Works
Ghrelin is a hormone your stomach produces when you’re hungry. Among other things, it signals your brain to release growth hormone. MK-677 mimics ghrelin by binding to the same receptor, effectively tricking your body into producing more growth hormone without injecting synthetic growth hormone directly. This makes it the first orally active compound in its class, known as a growth hormone secretagogue.
What separates MK-677 from injected growth hormone is its feedback loop. When growth hormone rises, a secondary hormone called IGF-1 also increases. That IGF-1 signals back to prevent excess growth hormone production, keeping levels elevated but within a physiological range. In clinical studies, MK-677 restored growth hormone pulses in older adults to levels typically seen in younger people.
Growth hormone peaks in plasma roughly one to two hours after taking MK-677. At a standard 25 mg dose, IGF-1 levels rose about 60% within six weeks and nearly 73% by 12 months in one trial.
Effects on Body Composition
MK-677’s appeal in fitness communities comes largely from its influence on lean mass and recovery. In clinical settings, results have been modest but measurable. One case report tracking body composition changes during a cycle found a 3.1% increase in total lean body mass and a 6.6% increase in trunk lean mass. However, fat mass also increased, rising 15.4% overall, with appendicular (limb) fat mass climbing nearly 15%. This aligns with what researchers know about ghrelin itself: unlike growth hormone, which tends to break down fat, ghrelin promotes fat storage.
Most of these body composition changes reversed after the person stopped taking the compound, with the exception of total fat mass and limb fat mass, which stayed elevated. So while MK-677 can shift your body composition, it doesn’t produce a clean “more muscle, less fat” effect on its own.
Bone Density and Turnover
Some of the more promising clinical research on MK-677 involves bone health, particularly in postmenopausal women at risk for osteoporosis. In one study, MK-677 increased osteocalcin (a marker of new bone formation) by 22% and a marker of bone breakdown by 41%. This means it accelerated overall bone turnover rather than simply building or breaking down bone.
When combined with alendronate, a standard osteoporosis drug, MK-677 produced a 4.2% increase in bone mineral density at the femoral neck (the top of the thigh bone near the hip), compared to 2.5% with alendronate alone. That difference was statistically significant. The combination didn’t show the same advantage at the spine, total hip, or total body, suggesting the bone benefits may be site-specific.
Sleep Quality Improvements
One of MK-677’s more consistent effects across studies is improved sleep. In young subjects, high-dose treatment increased deep sleep (stage IV) duration by roughly 50% and REM sleep by more than 20% compared to placebo. Sleep disruptions dropped dramatically, from 42% of nights under placebo to just 8% on MK-677.
Older adults saw similar benefits. REM sleep increased by nearly 50%, and the time it took to enter REM sleep shortened significantly. Because growth hormone is naturally released during deep sleep, these improvements may partly explain why users report feeling more recovered. The sleep effects are among the most reliably reported benefits in both clinical and anecdotal settings.
Side Effects and Metabolic Risks
The most common side effect is increased appetite, which makes sense given that MK-677 activates a hunger receptor. In one trial, 67% of people taking MK-677 reported increased appetite, compared to 36% on placebo. For people trying to stay lean, this can work against their goals. For elderly individuals losing weight involuntarily, it could theoretically help.
The more serious concern is blood sugar. At a 25 mg daily dose, fasting blood glucose rose about 25 to 27% above baseline within the first two to four weeks, climbing from a normal range into levels that would concern most doctors. Fasting insulin also increased. Researchers noted that it was unclear whether these metabolic effects would persist or worsen with long-term use, and this remains one of the biggest unresolved safety questions.
Other reported effects include mild water retention and joint stiffness, both of which are common with elevated growth hormone. One case report also documented unfavorable changes in cholesterol: LDL (“bad” cholesterol) rose 40%, HDL (“good” cholesterol) dropped 36%, and triglycerides climbed nearly 40%. Liver enzymes also spiked significantly. Most of these values returned to normal after stopping, but the lipid and liver changes during use were substantial.
Dosage Used in Studies
Clinical trials have used daily doses ranging from 5 mg to 25 mg. Even 5 mg produced a significant increase in growth hormone levels. The 25 mg dose is most commonly referenced in research and is the dose associated with the largest IGF-1 increases, but also with the most pronounced side effects on blood sugar and appetite. Dosing has typically been once daily in the evening, partly because growth hormone secretion naturally peaks during sleep.
Legal and Regulatory Status
MK-677 is not approved for human use by any regulatory health authority, including the FDA. It is classified by the World Anti-Doping Agency as a prohibited substance at all times, listed under growth hormone secretagogues alongside other ghrelin mimetics. It also falls under WADA’s broader category of non-approved substances, which covers drugs still in clinical development or discontinued from the approval pipeline.
Despite this, MK-677 is widely sold online as a “research chemical” or supplement. It is not a dietary supplement by any legal definition, and products sold this way have no regulatory oversight for purity, dosage accuracy, or contamination. Anyone considering it should understand that its long-term safety profile in humans has not been established, and the metabolic risks observed in short-term trials are not trivial.