MK-677 (ibutamoren) is not approved by the FDA for any medical use, and its safety has not been formally established. Clinical trials have identified several real side effects, most notably increased appetite, water retention, and a significant rise in fasting blood sugar. While some of these effects are mild and temporary, others, particularly the metabolic changes, raise genuine concerns for long-term use.
How MK-677 Works
MK-677 mimics a hunger hormone called ghrelin by binding to the same receptor in your brain. This triggers your pituitary gland to release more growth hormone, which in turn raises levels of IGF-1, a protein that promotes tissue growth throughout the body. Unlike growth hormone injections, MK-677 is taken as a pill and stimulates your body’s own growth hormone production rather than introducing an external hormone directly.
This distinction matters for safety. Because MK-677 works through your body’s natural signaling system, some side effects differ from those seen with injected growth hormone. Clinical trials noted fewer issues with carpal tunnel syndrome and breast tissue growth compared to direct growth hormone therapy. But “fewer side effects than injections” is not the same as “safe.”
The Most Common Side Effects
In a randomized controlled trial of healthy older adults published in the Annals of Internal Medicine, the most frequently reported side effects were increased appetite, mild swelling in the lower legs, and temporary muscle pain. About 67% of people taking MK-677 reported increased appetite, compared to 36% on placebo. The appetite boost typically subsided within a few months.
Mild swelling from water retention appeared in 44% of MK-677 users versus 27% on placebo. Temporary muscle pain affected 33% of users compared to 9% on placebo. Joint pain, interestingly, was actually more common in the placebo group (77%) than in the MK-677 group (58%), suggesting it wasn’t caused by the drug itself.
These side effects were generally described as mild and transient. For most people in clinical settings, they resolved on their own without stopping the drug.
Blood Sugar Is the Biggest Concern
The most worrying safety signal from clinical research involves blood sugar. In a study published in the Journal of Clinical Endocrinology and Metabolism, a 25 mg daily dose of MK-677 raised fasting blood glucose by roughly 25 to 27% within two to four weeks. Average fasting glucose went from 5.4 mmol/L (about 97 mg/dL, which is normal) to 6.8 mmol/L (about 122 mg/dL, which crosses into pre-diabetic territory).
Fasting insulin levels climbed too, rising from about 10.6 to 16.2 mU/L over four weeks at the 25 mg dose. This combination of higher blood sugar and higher insulin is the hallmark of insulin resistance, a precursor to type 2 diabetes. The effect was dose-dependent, meaning higher doses caused larger increases.
People with a higher BMI were more vulnerable. The correlation between BMI and glucose increase was strong (r = 0.77), meaning if you’re already carrying extra weight, MK-677 is more likely to push your blood sugar into an unhealthy range. For anyone with pre-existing insulin resistance, prediabetes, or a family history of diabetes, this risk is particularly relevant.
Effects on Sleep
One genuinely positive finding involves sleep quality. In a study published in Neuroendocrinology, MK-677 increased deep sleep (stage IV) duration by about 50% in younger subjects and boosted REM sleep by more than 20%. In older adults, REM sleep increased by nearly 50%, and people fell into REM sleep faster. These are meaningful improvements, as both deep sleep and REM sleep tend to decline with age.
Cortisol and Prolactin Appear Unaffected
Some users worry that MK-677 could raise cortisol (a stress hormone) or prolactin (a hormone linked to sexual side effects when elevated). In a clinical trial published in the Journal of Clinical Endocrinology and Metabolism, seven days of MK-677 use produced no significant increase in either cortisol or prolactin compared to placebo. This is reassuring, though it reflects short-term data rather than months of use.
Bone Density: Mixed Results
MK-677 increases markers of bone turnover, boosting both bone-building and bone-breakdown activity. In a 12-month trial of postmenopausal women with osteoporosis, MK-677 raised one marker of bone formation (osteocalcin) by 22% and a marker of bone breakdown by 41%. Despite ramping up bone activity, this didn’t translate into meaningful gains in bone density. The femoral neck (hip bone) saw a small increase, but total body bone density actually trended downward compared to placebo.
When combined with alendronate (a standard osteoporosis drug), MK-677 did enhance hip bone density slightly more than the drug alone, increasing it by 4.2% versus 2.5% at 18 months. But at other skeletal sites, the combination offered no additional benefit. In short, MK-677 is not a reliable bone-building tool on its own.
No FDA Approval, No Quality Control
As of 2025, the FDA has not approved MK-677 for any medical use. The agency has issued warning letters to companies selling it, explicitly stating that ibutamoren is an unapproved active ingredient whose safety and efficacy have not been established. Products sold online as MK-677 are classified as unapproved new drugs in violation of federal law.
This matters beyond legality. Without FDA oversight, there is no guarantee that what you buy actually contains MK-677 at the labeled dose, or that it’s free of contaminants. Independent testing of research chemicals sold online has repeatedly found inaccurate dosing and undisclosed ingredients. You’re essentially trusting an unregulated supply chain with a compound that already carries metabolic risks at known doses.
Who Faces the Most Risk
The clinical data points to specific groups who should be especially cautious. People who are overweight or obese face amplified blood sugar effects. Anyone with prediabetes, type 2 diabetes, or insulin resistance is at risk of worsening their metabolic health. Because MK-677 raises IGF-1, a growth factor that can promote cell proliferation, individuals with a history of cancer or active tumors face a theoretical but biologically plausible risk of accelerating disease.
For young, healthy people using MK-677 to build muscle or improve recovery, the risk profile is lower but not zero. The blood sugar effects occur even in healthy individuals, and the long-term consequences of chronically elevated IGF-1 in otherwise healthy people remain unstudied. The longest controlled trials lasted about two years, and most were conducted in older adults, not the young fitness-focused population that makes up most of the demand for this compound.