MK-677 (ibutamoren) is a pill that raises growth hormone by mimicking ghrelin, the “hunger hormone”. Merck designed it in the 1990s as an orally active growth hormone secretagogue.[1] In a two-year trial in older adults it added lean mass but raised blood sugar,[2] and a hip fracture trial was stopped early over heart failure concerns.[3] It is not FDA-approved.[13]
This profile covers whether MK-677 is a peptide or SARM, how it works, what clinical trials found, side effects, doses studied and why it is restricted.
Is MK-677 a peptide, SARM or steroid?
None of the three. MK-677 is a small “nonpeptide” molecule that works when swallowed, unlike injectable peptides such as ipamorelin.[24][6] It is not a SARM (selective androgen receptor modulator) or a steroid either: it acts on the ghrelin receptor, not on androgen receptors.[19] The confusion comes from marketing, since it is frequently sold alongside SARMs.[15]
How MK-677 works
MK-677 activates the ghrelin receptor in the brain and pituitary gland, triggering pulses of growth hormone, which raise IGF-1.[1] It works the same way as the peptide GHRP-6 but lasts long enough for once-daily dosing by mouth.[1] In older adults, 25 mg daily nearly doubled 24-hour growth hormone and raised IGF-1 from 141 to 265 micrograms per liter within four weeks.[8]
MK-677 benefits: what the research shows
- Lean mass in older adults: over two years, fat-free mass rose 1.1 kg versus a 0.5 kg loss on placebo. However, weight and limb fat also rose, and strength and physical function did not improve.[2]
- Obese men: eight weeks raised fat-free mass, but did not reduce total or belly fat.[5]
- Preventing muscle breakdown: during calorie restriction, MK-677 turned negative nitrogen balance (a sign of muscle loss) positive.[6]
- Sleep: in small studies, it increased deep sleep by about 50% and REM sleep by more than 20% in young men.[7]
- Bone: with alendronate, it raised hip bone density slightly more than alendronate alone (4.2% vs 2.5%), but not at other sites.[9]
- Hip fracture recovery: gait speed improved, but other function measures did not, and the trial was stopped early.[3][22]
- Alzheimer’s disease: a year of treatment in 563 patients had no effect on disease progression.[4]
- Children’s growth (as LUM-201): in a phase 2 trial, growth rates were good but lower than with standard growth hormone injections; a phase 3 trial began in 2026.[11][12]
MK-677 side effects
From the two-year trial in older adults:[2]
| Side effect | MK-677 | Placebo |
|---|---|---|
| Increased appetite | 67% | 36% |
| Swelling (edema) | 44% | 27% |
| Muscle pain | 33% | 9% |
- Blood sugar: fasting glucose rose about 5 mg/dL, insulin sensitivity fell, and HbA1c rose 0.2%.[2]
- Heart failure: a hip fracture trial was terminated early due to a congestive heart failure signal in a limited number of patients.[3] FDA cites this risk as the reason it considers ibutamoren a significant safety risk.[13]
- Testosterone: total testosterone fell in obese men, though free testosterone balance was unchanged.[23]
- Case reports: a man developed liver inflammation after two months of use.[20]
- Contaminated products: in a JAMA study of 44 online “SARM” products, 39% contained other unapproved drugs, including ibutamoren.[18] Athletes have been banned after ibutamoren turned up in contaminated supplements.[17]
Australian government-funded Healthy Male also lists anxiety and numbness among reported effects.[19]
MK-677 dosage: what has been studied
| Setting | Dose |
|---|---|
| Most adult trials | 25 mg by mouth once daily[2][3][4] |
| Other adult studies | 2 to 50 mg daily[8] |
| Children (as LUM-201) | 0.8 to 3.2 mg per kg per day; 1.6 mg/kg/day in phase 3[11][12] |
In the two-year trial, the dose was lowered to 10 mg in four people because of high blood sugar or joint pain.[2]
MK-677 research around the world
- Sweden: a series of studies in obese men examined body composition, bone, cholesterol and testosterone.[5][23]
- Belgium: sleep studies in young and older men.[7]
- Europe and Israel: multinational hip fracture trials.[22][3]
- Chile and Russia: a study in children with growth hormone deficiency.[24]
- France: a 2026 study showed ibutamoren can be detected in hair after a single dose.[25]
- Europe-wide: a network of medicine control labs in 13 countries found ibutamoren among the most common drugs in illegal performance products.[21]
What users report
Is MK-677 legal?
- Not FDA-approved for any use.[13]
- Not for compounding: FDA lists ibutamoren mesylate among substances with significant safety risks, and in October 2024 its advisory committee voted 1 to 13 against allowing it, citing fluid retention, congestive heart failure and high blood sugar.[13][14]
- Not a legal supplement: FDA has sent warning letters to companies selling it, and it is on the Department of Defense’s prohibited dietary supplement ingredients list.[15]
- Banned in sport: WADA names ibutamoren as a prohibited growth hormone secretagogue, banned at all times.[16]
This is general information, not legal advice.
MK-677 vs ipamorelin and tesamorelin
MK-677 and ipamorelin both activate the ghrelin receptor, but MK-677 is a daily pill while ipamorelin is an injected peptide with a 2-hour half-life (see our CJC-1295 + ipamorelin guide). Tesamorelin works through the GHRH receptor instead and is the only one of the three that is FDA-approved.