What does the research show about mk-677?

MK-677

Grey marketNot approved for human use in the US, and sold anyway.

In a 1-year trial of healthy older adults, MK-677 raised fat-free mass 1.1 kg against a 0.5 kg loss on placebo, with no change in strength, function or body fat. Fasting glucose rose and insulin sensitivity fell. A trial in hip fracture patients was stopped early for a heart failure signal. It is not approved.

Add to Bio HackChecked 2026-11-09

Status: Investigational in the US. Not FDA-approved for any use. It is not a peptide. It is an orally taken, non-peptide growth hormone secretagogue. FDA lists ibutamoren mesylate in category 2 of bulk substances for compounding, citing a heart failure signal. Prohibited at all times by WADA (S2).
Also called: ibutamoren, ibutamoren mesylate, MK-0677, nutrobal, ghrelin mimetic, growth hormone secretagogue
Taken for: muscle, lean mass, strength, fat loss, growth hormone, recovery, appetite

Strong several reviews agree · Moderate one review or consistent trials · Limited one or a few small studies · Untested no study in people, listed with what it rests on

Shown to help1

ModerateShown to add about 1.1 kg of fat-free mass over a year in older adults, against a 0.5 kg loss on placebo. Body weight also rose.

Reported risks6

ModerateShown to raise fasting blood sugar about 5 mg/dL and lower insulin sensitivity in older adults, with poorer glucose handling in obese men.How often is not known
LimitedOne trial after hip fracture was stopped early for a heart failure signal. FDA placed it in category 2 for compounding, citing heart failure risk.How often is not known
LimitedOne trial found more appetite, mild leg swelling and muscle pain, with weight up 2.7 kg against 0.8 kg on placebo, in older adults.How often is not known
LimitedSmall trials found mixed results: cortisol rose in older adults and did not rise in obese men.How often is not known
LimitedFDA warning letters state products sold as MK-677 are unapproved new drugs. Of 44 online SARM products, 39% contained other unapproved drugs.How often is not known
LimitedWADA lists ibutamoren (MK-677) as a growth hormone secretagogue, prohibited at all times in sport.How often is not known

What people take it for, and what was found

Shown to help1

Moderate

Fat-free mass

Shown to add about 1.1 kg of fat-free mass over a year in older adults, against a 0.5 kg loss on placebo. Body weight also rose.

The numbers and sources

Effect: At 12 months, fat-free mass changed by +1.1 kg (95% CI 0.7 to 1.5) on MK-677 and -0.5 kg (95% CI -1.1 to 0.2) on placebo. Intracellular water, a marker of body cell mass, changed by +0.8 kg against -1.0 kg [1]. In obese men over 8 weeks, fat-free mass rose on MK-677 compared with placebo by DEXA and by a four-compartment model [2].
Population: 65 healthy adults aged 60 to 81, over 2 years [1]; 24 obese men aged 18 to 50, BMI over 30 [2].
Sources: [1], [2]
Caveats: Fat-free mass includes water, organs and bone, not only muscle. Body weight also rose 2.7 kg against 0.8 kg on placebo [1].

Not shown to help1

Limited

Strength and physical function

Limited evidence: added fat-free mass did not change strength in older adults, and after hip fracture only gait speed improved over placebo.

The numbers and sources

Effect: In healthy older adults, the gain in fat-free mass did not change strength or function [1]. After hip fracture, stair climbing power rose 12.5 W more than placebo (95% CI -10.95 to 35.88, not significant), and gait speed improved by a 0.7-point score difference (95% CI 0.17 to 1.28). Several other functional measures did not improve [3].
Population: 65 older adults [1]; 123 older adults recovering from hip fracture, 24 weeks [3].
Sources: [1], [3]
Caveats: The older-adult trial was not powered for function [1]. The hip fracture trial was stopped early [3].

Risks

Reported risks5

LimitedHow often is not known

Heart failure signal

One trial after hip fracture was stopped early for a heart failure signal. FDA placed it in category 2 for compounding, citing heart failure risk.

The numbers and sources

How common: How often is not known: the sources give no rate.
Effect: The hip fracture trial was terminated early because of a safety signal of congestive heart failure in a limited number of patients. The authors describe an unfavorable safety profile in that population [3]. FDA placed ibutamoren mesylate in category 2 for compounding under both 503A and 503B, citing the potential for congestive heart failure and this trial [4].
Population: 123 older adults after hip fracture [3]; US compounding [4].
Sources: [3], [4]
Caveats: The abstract does not give the number of heart failure cases [3].

ModerateHow often is not known

Raised blood sugar and lower insulin sensitivity

Shown to raise fasting blood sugar about 5 mg/dL and lower insulin sensitivity in older adults, with poorer glucose handling in obese men.

The numbers and sources

How common: How often is not known: the sources give no rate.
Effect: Fasting blood glucose rose an average of 0.3 mmol/L (5 mg/dL) on MK-677, and insulin sensitivity fell [1]. In obese men, fasting glucose and insulin did not change, but an oral glucose tolerance test showed impaired glucose handling at 2 and 8 weeks [2].
Population: 65 older adults [1]; 24 obese men [2].
Sources: [1], [2]
Caveats: Two small trials.

LimitedHow often is not known

Appetite, weight gain, swelling and muscle pain

One trial found more appetite, mild leg swelling and muscle pain, with weight up 2.7 kg against 0.8 kg on placebo, in older adults.

The numbers and sources

How common: How often is not known: the sources give no rate.
Effect: The most frequent side effects were increased appetite that subsided within a few months, and transient, mild swelling of the legs and muscle pain. Body weight rose 2.7 kg against 0.8 kg on placebo, and limb fat rose 1.1 kg against 0.24 kg [1].
Population: 65 healthy adults aged 60 to 81 [1].
Sources: [1]
Caveats: One trial.

LimitedHow often is not known

Products sold online and FDA warning letters

FDA warning letters state products sold as MK-677 are unapproved new drugs. Of 44 online SARM products, 39% contained other unapproved drugs.

The numbers and sources

How common: How often is not known: the sources give no rate.
Effect: Of 44 products sold online as SARMs, 17 (39%) contained another unapproved drug, including ibutamoren [5]. FDA warning letters in 2023 and 2025 told sellers that products marketed as "MK-677 Ibutamoren" were unapproved new drugs, despite labels saying they were for research only [6][7].
Population: Products bought online in 2016 [5]; US sellers [6][7].
Sources: [5], [6], [7]
Caveats: The labeling study tested products sold as SARMs, not products sold as MK-677 [5].

LimitedHow often is not known

Prohibited in sport

WADA lists ibutamoren (MK-677) as a growth hormone secretagogue, prohibited at all times in sport.

The numbers and sources

How common: How often is not known: the sources give no rate.
Effect: WADA lists ibutamoren (MK-677) as a growth hormone secretagogue under S2, prohibited at all times [8].
Population: Athletes subject to the World Anti-Doping Code [8].
Sources: [8]
Caveats: A sport rule, not a health finding.

Mixed results1

LimitedHow often is not known

Cortisol

Small trials found mixed results: cortisol rose in older adults and did not rise in obese men.

The numbers and sources

How common: How often is not known: the sources give no rate.
Effect: Cortisol rose 47 nmol/L (1.7 micrograms/dL) on MK-677 [1]. In obese men, cortisol was not raised at 2 or 8 weeks [2].
Population: 65 older adults [1]; 24 obese men [2].
Sources: [1], [2]
Caveats: The two trials disagree.

Claims tested and not found

That MK-677 reduces body fat. In older adults, visceral fat and total fat mass did not differ from placebo over a year [1]. In obese men, total and visceral fat did not change over 8 weeks [2].

Sources

Nass R, Pezzoli SS, Oliveri MC, 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. https://doi.org/10.7326/0003-4819-149-9-200811040-00003
Svensson J, Lonn L, Jansson JO, et al. Two-Month Treatment of Obese Subjects with the Oral Growth Hormone (GH) Secretagogue MK-677 Increases GH Secretion, Fat-Free Mass, and Energy Expenditure. Journal of Clinical Endocrinology and Metabolism. 1998. https://doi.org/10.1210/jcem.83.2.4539
Adunsky A, Chandler J, Heyden N, et al. MK-0677 (ibutamoren mesylate) for the treatment of patients recovering from hip fracture: a multicenter, randomized, placebo-controlled phase IIb study. Archives of Gerontology and Geriatrics. 2011. https://doi.org/10.1016/j.archger.2010.10.004
U.S. Food and Drug Administration. Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks. 2026. https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks
Van Wagoner RM, Eichner A, Bhasin S, et al. Chemical Composition and Labeling of Substances Marketed as Selective Androgen Receptor Modulators and Sold via the Internet. JAMA. 2017. https://doi.org/10.1001/jama.2017.17069
U.S. Food and Drug Administration. Warning Letter: Warrior Labz SARMS, MARCS-CMS 655280. 2023. https://www.fda.gov/inspections-compliance-enforcement-and-criminal-investigations/warning-letters/warrior-labz-sarms-655280-06122023
U.S. Food and Drug Administration. Warning Letter: Dynamic Health Group dba SARMS AMERICA, MARCS-CMS 719257. 2025. https://www.fda.gov/inspections-compliance-enforcement-and-criminal-investigations/warning-letters/dynamic-health-group-dba-sarms-america-719257-12122025
World Anti-Doping Agency. The Prohibited List. 2026. https://www.wada-ama.org/en/prohibited-list

Everything in the library