MK-677 (Ibutamoren)

An orally active, non-peptide ghrelin receptor (GHS-R1a) agonist developed by Merck that raises pulsatile growth hormone and IGF-1 secretion; adult programs were discontinued, and the molecule is now in pediatric Phase 3 trials as LUM-201.

Also referenced as: Ibutamoren, Ibutamoren mesylate, MK-0677, L-163,191, LUM-201, Nutrobal, Oratrope

Also appears in: Performance

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Flat vs. Jun 23

Current low$3.67/mg

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COA Public product evidence 3 certificate records for MK-677 (Ibutamoren) products, from 3 vendors 2 reference a report on the testing laboratory's own system · 1 has a laboratory lookup that answered when last checked · 3 match a vendor product page at the same address →

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What is MK-677 (Ibutamoren)?

MK-677 (ibutamoren, usually supplied as ibutamoren mesylate) is a synthetic spiropiperidine small molecule designed at Merck in the early 1990s as an orally active mimetic of the growth hormone-releasing peptide GHRP-6 (Patchett et al., Proceedings of the National Academy of Sciences, 1995). It is not a peptide: it was built specifically to reproduce the growth hormone-releasing activity of peptide secretagogues in a molecule that survives oral administration and, with once-daily dosing, keeps growth hormone and IGF-1 elevated across the full dosing interval. It appears in the research-compound market because it is one of the few orally dosed agents that reliably raises growth hormone and IGF-1 in humans, and it remains in formal clinical development under the code LUM-201 for pediatric growth hormone deficiency.

How it works

• Agonist at the ghrelin receptor (GHS-R1a) — MK-677 was the tool compound used to clone the growth hormone secretagogue receptor in pituitary and hypothalamus (Howard et al., Science, 1996); the receptor’s endogenous ligand, ghrelin, was identified afterward, so MK-677 is often described as a ghrelin mimetic.
• Amplifies existing pulsatile growth hormone release — in healthy adults aged 64 to 81, once-daily oral MK-677 roughly doubled mean 24-hour growth hormone concentration at 25 mg and raised serum IGF-1 into the young-adult range within two to four weeks, by increasing the height of pulses and interpulse nadirs rather than the number of pulses (Chapman et al., Journal of Clinical Endocrinology & Metabolism, 1996).
• Carries ghrelin-like effects beyond growth hormone — human studies consistently report increased appetite and a modest prolactin rise; fasting glucose rose in older adults (Chapman et al., 1996; Nass et al., Annals of Internal Medicine, 2008), oral glucose tolerance worsened in obese young men even though fasting glucose did not change (Svensson et al., Journal of Clinical Endocrinology & Metabolism, 1998), and cortisol was unchanged or only transiently raised in short studies but increased over a year of dosing (Nass et al., 2008).
• Anabolic downstream signals via IGF-1 — short-term studies showed reversal of diet-induced nitrogen wasting in calorie-restricted volunteers (Murphy et al., Journal of Clinical Endocrinology & Metabolism, 1998) and an increase in fat-free mass, with a transient rise in basal metabolic rate, in obese men over eight weeks (Svensson et al., 1998).

Research status

MK-677 has one of the deeper human-trial records of any compound in the growth hormone secretagogue category, and most of that record is negative on clinical outcomes despite consistent target engagement.

Merck adult programs (1996 to 2011), all discontinued:

• Chapman et al. (1996), Journal of Clinical Endocrinology & Metabolism, 81(12):4249–4257 — dose-ranging study in 32 healthy elderly subjects establishing the growth hormone and IGF-1 response at 2, 10, and 25 mg; fasting glucose rose at 25 mg while cortisol did not change.
• Murphy et al. (1998), Journal of Clinical Endocrinology & Metabolism, 83(2):320–325 — eight healthy volunteers; 25 mg reversed diet-induced negative nitrogen balance.
• Svensson et al. (1998), Journal of Clinical Endocrinology & Metabolism, 83(2):362–369 — 24 obese men, 8 weeks; IGF-1 rose about 40%, fat-free mass increased, visceral fat did not change, basal metabolic rate rose at 2 weeks but not at 8, and an oral glucose tolerance test worsened while fasting glucose and insulin were unchanged.
• Copinschi et al. (1997), Neuroendocrinology, 66(4):278–286 — small study reporting changes in sleep architecture in young and older men.
• Murphy et al. (2001), Journal of Clinical Endocrinology & Metabolism, 86(3):1116–1125 — 292 postmenopausal women with osteoporosis; MK-677 plus alendronate improved femoral neck bone mineral density versus alendronate alone (4.2% vs 2.5%) but not lumbar spine, total hip, or total body, and the authors flagged that gap as a concern when weighed against growth hormone-related side effects.
• Bach et al. (2004), Journal of the American Geriatrics Society, 52(4):516–523 — 161 hip fracture patients; IGF-1 rose 84% versus 17% on placebo, functional measures trended in favor of MK-0677 without reaching statistical significance, and the uncertain signal motivated the later Phase IIb trial.
• Nass et al. (2008), Annals of Internal Medicine, 149(9):601–611 — 65 healthy adults aged 60 to 81, two-year double-blind placebo-controlled trial at 25 mg daily. Fat-free mass rose 1.1 kg versus a 0.5 kg loss on placebo, but there was no change in abdominal visceral fat, strength, or function; fasting glucose increased, insulin sensitivity decreased, and cortisol rose. The most common side effects were appetite increase, lower-extremity edema, and muscle pain.
• Sevigny et al. (2008), Neurology, 71(21):1702–1708 — 563 patients with mild to moderate Alzheimer disease, 12 months at 25 mg daily. Serum IGF-1 rose 60 to 73%, yet there was no difference from placebo on any cognitive or functional endpoint.
• Adunsky et al. (2011), Archives of Gerontology and Geriatrics, 53(2):183–189 — multicenter Phase IIb trial in 123 elderly hip fracture patients at 25 mg daily. The trial was terminated early because of a congestive heart failure safety signal; IGF-1 increased but most functional measures did not improve, and the authors concluded MK-677 “has an unfavorable safety profile in this patient population.” Merck did not advance the compound to a marketing application, and no approval exists anywhere.

LUM-201 pediatric program (Lumos Pharma, 2020 to present): Lumos Pharma licensed ibutamoren mesylate from Ammonett Pharma in 2018 and is developing it as LUM-201, an oral alternative to injected growth hormone for children with moderate idiopathic growth hormone deficiency who retain some pituitary function. Lumos was acquired by Double Point Ventures and taken private in December 2024; the program continued. Registered studies as of October 2026:

• OraGrowtH210 (NCT04614337), Phase 2, 104 children, completed September 2024 with results posted on ClinicalTrials.gov in June 2026; OraGrowtH212 (NCT04806854), a Phase 2 pharmacokinetic/pharmacodynamic study; OraGrowtH213 (NCT05250063), an extension study completed January 2025 with results posted in April 2026; and OraGrowtH211 (NCT05796440), a long-term safety study. The sponsor has stated that OraGrowtH210 and OraGrowtH212 met their primary and secondary endpoints; the published trial registry results are the primary record.
• Phase 3 (NCT06948214), a 12-month randomized, double-blind, placebo-controlled trial of daily oral LUM-201 at 1.6 mg/kg/day in about 150 treatment-naive children aged 3 to 11, began May 2026 and is listed as recruiting with an estimated primary completion of December 2027. A long-term safety extension (NCT07129759) is registered to start in 2027.
• Lumos has also registered a Phase 2 trial of LUM-201 as an adjunct to semaglutide for physical function in older adults with obesity (NCT07754045, not yet recruiting, planned 2027).

Independent academic work: a Massachusetts General Hospital pilot of ibutamoren in nonalcoholic fatty liver disease (NCT05364684, 12 participants) completed in late 2024 with results posted in January 2026.

As of October 2026, MK-677 / ibutamoren is not approved by the FDA or any other national regulator for any indication.

Common dosage forms

In clinical development, ibutamoren mesylate is an oral solid tested against matched placebo capsules. On the research market it is sold as oral capsules (typically 10 to 25 mg per capsule), as a liquid solution or suspension dispensed by dropper or syringe, as tablets, and as raw powder. It is not an injectable product, which distinguishes it from peptide secretagogues such as GHRP-6, ipamorelin, or hexarelin that are sold as lyophilized vials.

Key considerations

• Not a peptide, and not a SARM. MK-677 is a spiropiperidine small molecule. It is routinely grouped with peptides because it acts on the same receptor as GHRP-class peptides, and it is routinely grouped with SARMs by vendors even though it has no androgen receptor activity. FDA warning letters issued in December 2025 to sellers marketing it alongside SARMs classify MK-677 ibutamoren as an unapproved new drug under section 505(a) of the FD&C Act.
• Status is Investigational because of the pediatric program only. The Investigational status reflects active registered human development, namely the LUM-201 Phase 3 trial that started in 2026 and is recruiting. Every adult indication Merck pursued (frailty, body composition, osteoporosis, hip fracture recovery, Alzheimer disease) was discontinued, so the adult evidence base should be read as a completed and largely negative program, not as ongoing development.
• Cardiovascular and metabolic safety signals are documented in controlled trials. The 2011 hip fracture trial was stopped for a congestive heart failure signal in the MK-677 arm; multiple trials report higher fasting glucose, reduced insulin sensitivity, or impaired oral glucose tolerance; peripheral edema, muscle pain, and raised prolactin are recurrent findings, and cortisol rose over a year of dosing in older adults. These are growth hormone and ghrelin class effects in frail or metabolically vulnerable populations, not idiosyncratic events.
• Biomarker response has not translated into functional outcomes. Across the Bach, Nass, Sevigny, and Adunsky trials, IGF-1 rose reliably while strength, physical function, and cognition did not improve. Claims built on IGF-1 or lean-mass changes alone overstate what the human data support.
• Naming and salt-form confusion. Ibutamoren, ibutamoren mesylate, MK-0677, L-163,191, and LUM-201 all refer to the same molecule, as do Nutrobal (a research-market brand) and Oratrope (a former Ammonett Pharma development name). “MK-677” is the same compound as the Phase 3 pediatric candidate; the clinical program does not imply that research-market material is pharmaceutical grade or that the adult safety findings no longer apply.
• Prohibited in sport. It is a named example under WADA’s S2 growth-hormone secretagogue provisions, within the class of peptide hormones, growth factors, related substances, and mimetics, and is banned at all times.