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MK-677 (Ibutamoren): Why It Is Not a Peptide

MK-677 (ibutamoren) is a small-molecule pill that raises growth hormone, not a peptide; this page covers trial results, risks, regulator warnings and anti-doping status.

Content last updated . This page has not been medically reviewed.

Quick answer
MK-677, also called ibutamoren, is often sold next to peptides, but it is not one. It is a "non-peptide" (small-molecule) compound that switches on the ghrelin receptor, the same receptor the hunger hormone ghrelin uses, and so raises growth hormone and IGF-1. [1][2] It has never been shown to be a safe, effective treatment for any condition we could find. Where trials exist, hormone numbers rose, but most function outcomes did not, and a hip-fracture trial stopped early over a heart-failure signal. [3] Evidence labels used here: promising but limited, mixed, no good evidence of benefit (for the outcomes tested), evidence of harm, and marketing claim. A rise in IGF-1 or growth hormone is a biomarker, not a health outcome.

Why "not a peptide" matters

A peptide is a short chain of amino acids. See What Are Peptides?. Ibutamoren is described in the research literature as an orally active "nonpeptide mimic" of growth-hormone-releasing peptide, [4] and as a non-peptide agonist and investigational new drug in a 2021 structural study. [1] The trials above gave it by mouth; for why many peptides are handled differently, see Why Peptides Are Often Broken Down During Digestion. Treating it as a "peptide" blurs its evidence and its risks, which are its own. The peptide-like ghrelin-receptor drugs are covered in Ghrelin and Growth-Hormone Secretagogues.

Human trials, kept apart

All results are from the study populations named; none was a trial of use for physique or performance in healthy young people.
StudyPeople and designWhat happened
1998, obese men24 men, randomized, placebo-controlled, 8 weeksIGF-I rose about 40%; fat-free mass rose; total and visceral fat did not change significantly; a glucose tolerance test showed impaired glucose handling. [5]
2008, healthy older adults65 people aged 60 to 81, placebo-controlled, 2 yearsGrowth hormone and IGF-I rose to young-adult levels; fat-free mass rose (1.1 kg vs a 0.5 kg fall on placebo); body weight and limb fat rose; fasting glucose rose and insulin sensitivity fell; cortisol rose; strength and function did not change. Authors judged it generally well tolerated and the study too small to test function. [6]
2011, hip fracture123 older patients, randomized, placebo-controlled, 24 weeksIGF-1 rose, but most functional measures did not improve (gait speed did). Trial ended early over a safety signal of congestive heart failure; authors called the safety profile unfavorable in this group. [3]
2008, Alzheimer disease563 patients, 12 monthsIGF-1 rose 72.9%, yet no benefit on disease progression. [7]
2001, children with GH deficiency18 children, 7 to 8 daysGH, IGF-I and IGFBP-3 rose in some children; a short safety and hormone study only. [2]

In plain terms: the compound does raise hormone levels. Whether that helps anyone in daily life has not been shown in these trials, and no good evidence of benefit was found for the function outcomes tested. A 2018 review also noted concern about higher blood glucose through lower insulin sensitivity and called for long-term data, including cancer incidence. [8]

Known and reported harms

  • From trials: appetite increase, brief mild leg swelling and muscle pain, higher fasting glucose and lower insulin sensitivity, raised cortisol, weight gain. [6]
  • Heart failure signal in older hip-fracture patients. [3] The FDA cites this trial in its reasoning on ibutamoren. [9]
  • Liver: a 2025 case report describes raised liver enzymes in an otherwise healthy man in his early 30s after about 2 months of MK-677, which returned to normal after stopping. [10] One case cannot show how common this is.

Quality and what is really in products

MK-677 is often found where it is not labeled. In a 2017 JAMA analysis of 44 products sold online as SARMs, 17 (39%) contained another unapproved drug, including ibutamoren; only 41% matched the amounts on the label. [15] A European laboratory network (2025) examined 324 samples of suspected illegal SARM, metabolic modulator and growth hormone secretagogue products; ibutamoren was the most-reported of 18 molecules, 24% were presented as dietary supplements, and some were overdosed. [16] See Peptide Safety for wider product-quality issues.

Special groups

Older adults with fracture or heart disease are the group where a heart-failure signal appeared. [3] People with diabetes or prediabetes should note the glucose findings. [6] We found no sourced guidance for pregnancy or for children outside the supervised trials above. Anyone taking it who feels unwell, or who has swelling, breathlessness or yellow skin, should seek medical care and tell the clinician about the product.

Frequently asked questions

Is MK-677 a peptide or a SARM?

Neither. It is a non-peptide growth hormone secretagogue acting on the ghrelin receptor. [1] It is sold alongside SARMs, and has turned up in products sold as SARMs. [15]

Does MK-677 build muscle?

In a 2-year trial in older adults, fat-free mass rose but strength and function did not change. [6] That does not show a practical benefit.

Is MK-677 approved?

We read no approval. The FDA lists it among bulk substances with significant safety risks for compounding. [9] It is being studied by a company as LUM-201 for childhood growth hormone deficiency. [13]

Is MK-677 banned in sport?

It is named in the WADA Prohibited List under S2, prohibited at all times. [14]

Why did one trial stop early?

A hip-fracture trial ended because of a safety signal of congestive heart failure. [3]

More details: evidence, limits and cautions

The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.

Regulatory and anti-doping position (read 2026-10-22; not legal advice)
  • United States (FDA). The FDA's category 2 list of bulk drug substances for compounding that may present significant safety risks includes ibutamoren mesylate (added September 29, 2023 for section 503A; December 29, 2022 for 503B), citing the potential for congestive heart failure in certain patients. [9] We did not read an FDA approval for it. A separate FDA consumer update says SARMs are unapproved drugs; that page is about SARMs and does not name ibutamoren. [11]
  • Other countries. Not verified for the UK, EU, Canada and Australia in sources we could read.
  • Registered research. Ibutamoren, under the code LUM-201, is in a phase 3 trial in children with growth hormone deficiency (NCT06948214, recruiting, estimated 150 children), a company-sponsored study; the registry does not report results. [12][13] A small phase 2 trial in fatty liver (12 participants) is marked completed. [12] Registered is not approved.
  • Sport. The WADA Prohibited List, class S2 (prohibited at all times), names ibutamoren (MK-677) among growth hormone secretagogues. [14] See Sports Anti-Doping Rules for Peptides.
References
  1. Structural basis of human ghrelin receptor signaling by ghrelin and the synthetic agonist ibutamoren. Nat Commun 2021. Read 2026-10-22.
  2. Effects of oral administration of ibutamoren mesylate, a nonpeptide growth hormone secretagogue, in growth hormone-deficient children. Clin Pharmacol Ther 2001. Read 2026-10-22.
  3. MK-0677 (ibutamoren mesylate) for the treatment of patients recovering from hip fracture: a multicenter, randomized, placebo-controlled phase IIb study. Arch Gerontol Geriatr 2011. Read 2026-10-22.
  4. MK-677, an orally active growth hormone secretagogue, reverses diet-induced catabolism. J Clin Endocrinol Metab 1998. Read 2026-10-22.
  5. Two-month treatment of obese subjects with the oral GH secretagogue MK-677 increases GH secretion, fat-free mass, and energy expenditure. J Clin Endocrinol Metab 1998. Read 2026-10-22.
  6. Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults: a randomized trial. Ann Intern Med 2008. Read 2026-10-22.
  7. Growth hormone secretagogue MK-677: no clinical effect on AD progression in a randomized trial. Neurology 2008. Read 2026-10-22.
  8. The Safety and Efficacy of Growth Hormone Secretagogues. Sex Med Rev 2018. Read 2026-10-22.
  9. U.S. Food and Drug Administration: Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks (category 2 list). Content current as of 04/22/2026. Read 2026-10-22.
  10. Hepatotoxicity induced by MK-677. BMJ Case Rep 2025. Read 2026-10-22.
  11. U.S. Food and Drug Administration: FDA Warns of Use of Selective Androgen Receptor Modulators (SARMs) Among Teens, Young Adults (consumer update). Page text read via an Internet Archive copy. Read 2026-10-22.
  12. ClinicalTrials.gov record NCT05364684: The impact of ibutamoren on nonalcoholic fatty liver disease. Read 2026-10-22 (registry API).
  13. ClinicalTrials.gov record NCT06948214: Phase 3 study of LUM-201 in children with growth hormone deficiency. Read 2026-10-22 (registry API).
  14. World Anti-Doping Agency: The Prohibited List (2026 list page, class S2 and S0). Read 2026-10-22.
  15. Chemical Composition and Labeling of Substances Marketed as Selective Androgen Receptor Modulators and Sold via the Internet. JAMA 2017. Read 2026-10-22.
  16. SARMs, Metabolic Modulators and Growth Hormone Secretagogues in Suspected Illegal Medicines, Bought as Sport Performance Enhancers (GEON study). Drug Test Anal 2025. Read 2026-10-22.
Education, not medical advice. This page is for general information. It does not diagnose or treat any condition and is not a substitute for care from a qualified health professional. Natural does not automatically mean safe. Ask a clinician or pharmacist before changing your care, especially if you take medication, are pregnant or breastfeeding, or have a health condition.