MK-677 (Ibutamoren) Phase III Complete

What It Is

MK-677, also known as ibutamoren (and historically as L-163,191), is an orally active, non-peptide small molecule that mimics the action of the hormone ghrelin at the growth hormone secretagogue receptor (GHSR-1a). It was discovered and developed by Merck Research Laboratories in the 1990s as part of a program to find an oral growth hormone secretagogue — a drug that could elevate endogenous growth hormone (GH) and downstream IGF-1 through a natural pulsatile mechanism, without the injection burden and peaks of recombinant GH therapy.

Mechanistically, MK-677 is often grouped with peptide ghrelin-receptor agonists like GHRP-6, GHRP-2, hexarelin, and ipamorelin. Functionally, it is distinct from all of them in one decisive way: MK-677 is orally bioavailable, while the peptide secretagogues all require subcutaneous injection. That single feature has made MK-677 the most widely used growth-hormone-axis compound in community and "biohacking" settings despite being chemically a small molecule rather than a peptide.

Merck advanced MK-677 through multiple Phase 2 and Phase 3 trials across several indications — GH deficiency in adults, frailty and functional impairment in older adults, post-hip-fracture recovery, obesity, and postmenopausal osteoporosis — before discontinuing the program without a commercial approval. The published human dataset includes the widely-cited 12-month randomized controlled trial of 65 healthy older adults by Nass et al. (Ann Intern Med 2008; PMID 18981485), the Murphy postmenopausal osteoporosis trials, the Bach and Adunsky hip-fracture studies, and the Svensson obesity study. This is one of the most comprehensive human datasets of any GH-axis agent still used off-label, which is part of why it remains so influential in the "research" space.

MK-677 is not FDA-approved, is banned by the World Anti-Doping Agency (WADA), and was added to the FDA Category 2 Bulk Drug Substances list in 2024, making it ineligible for use by traditional compounding pharmacies under sections 503A/503B. Despite this, ibutamoren is the most common oral product sold in gray-market "research chemical" channels and is also widely repackaged as a supplement-like capsule despite being a regulated drug candidate.

Mechanism of Action

MK-677 is pharmacologically a ghrelin mimetic — it binds and activates the same receptor that endogenous ghrelin targets to drive GH release, appetite, and other downstream effects. The downstream endocrine phenotype is specific and well-characterized.

• GHSR-1a agonism (primary mechanism) — MK-677 binds with high affinity to the growth hormone secretagogue receptor type 1a in the anterior pituitary and hypothalamus. GHSR-1a activation drives Gq/11 → phospholipase C → IP3/DAG → intracellular calcium → GH release from somatotrophs. A 2021 cryo-EM structural paper (Nature Communications) resolved the binding mode of ibutamoren at GHSR-1a alongside endogenous ghrelin, confirming shared binding pocket with distinct residue contacts.
• GH pulse amplitude + frequency — Rather than inducing a single high GH spike, MK-677 increases the amplitude and to some extent the frequency of natural pulsatile GH release, preserving the endogenous rhythm. In the Nass trial, MK-677 restored GH levels in older adults to those typical of young adults.
• Somatostatin antagonism + GHRH synergy — MK-677 has been shown to amplify GHRH signaling in the pituitary and blunt somatostatin's inhibitory tone. This creates a favorable environment for GH secretion that does not require exogenous GHRH or GHRP administration.
• IGF-1 elevation (downstream) — Elevated GH pulses drive hepatic IGF-1 synthesis. Clinical data show ~40–80% increases in total serum IGF-1 in older adults after weeks of MK-677 therapy, generally into the mid-to-upper-normal range for healthy young adults.
• Appetite stimulation — Ghrelin is the "hunger hormone," and GHSR-1a activation in the hypothalamic arcuate nucleus drives NPY/AgRP orexigenic signaling. MK-677 meaningfully increases appetite in most users — useful for weight/muscle gain, less useful for lean-mass preservation during a deficit.
• Cortisol and prolactin selectivity — Unlike some earlier GH secretagogues, MK-677 is relatively selective for GH axis activation; cortisol and prolactin elevations are mild compared to GHRP-6 or hexarelin.
• Slow-wave sleep (SWS) effect — Increased GH release during early sleep is a natural physiological pattern, and MK-677 amplifies that. Some trials document increased stage 3/4 sleep and REM density; user reports commonly describe intense, vivid dreaming.
• Insulin signaling modulation — Elevated GH and IGF-1 tone antagonizes insulin action at the peripheral tissue level (lipolysis, hepatic glucose output). This is the mechanistic basis for MK-677's dose-dependent impact on fasting glucose and HbA1c in longer trials (Nass 2008).

What the Research Shows

The MK-677 human evidence base is unusually deep for a non-approved compound because Merck ran a serious clinical development program. Key findings:

• Healthy older adults — 12-month RCT (Nass et al., Ann Intern Med 2008; PMID 18981485) — 65 healthy adults aged 60–81 randomized to MK-677 25 mg/day vs placebo for 12 months. Results: GH and IGF-1 restored to healthy-young-adult levels, fat-free mass increased by 1.1 kg (vs −0.5 kg placebo), no improvement in strength or physical function, and worsening of insulin sensitivity. This is the single most-cited MK-677 paper and sets the realistic expectation ceiling.
• Postmenopausal osteoporosis (Murphy et al., JCEM 2001; PMID 11238495) — 292 women with osteoporosis randomized to alendronate, MK-677, combination, or placebo for 12–18 months. MK-677 alone did not produce significant BMD gains at most sites; combination with alendronate attenuated alendronate's suppressive effect on bone formation but did not add BMD at sites other than femoral neck.
• Elderly bone turnover (Murphy et al., JBMR 1999) — 187 healthy and functionally impaired elderly adults. MK-677 increased osteocalcin and urinary N-telopeptide (markers of bone turnover), consistent with amplified bone remodeling without clear net BMD effect.
• Obese young males (Svensson et al., JCEM 1998; PMID 9661080) — 8-week trial with MK-677 in obese subjects. Increases in GH, IGF-1, fat-free mass, and energy expenditure; increases in bone turnover markers.
• Hip fracture recovery — Bach trial — Randomized, double-blinded, placebo-controlled study of MK-677 in elderly hip-fracture recovery. Measured functional outcomes and safety over 6 months.
• Hip fracture recovery — Adunsky trial — Parallel study in 123 elderly hip-fracture patients, terminated early due to an observed increase in congestive heart failure (6.5% ibutamoren vs 1.7% placebo). This is the single most important safety signal in the MK-677 literature and is why the compound is specifically contraindicated in adults with preexisting CHF.
• GH deficiency adults — Merck-era Phase 2 trials showed MK-677 restored GH/IGF-1 in adult GHD patients with oral dosing, supporting the original development hypothesis.
• Short-term healthy subjects — Multiple shorter-duration studies showed consistent GH/IGF-1 elevation, increased fat-free mass, and dose-dependent appetite stimulation at 10–25 mg oral daily.
• Structural pharmacology (Nature Communications 2021) — Cryo-EM characterization of ibutamoren bound to GHSR-1a, clarifying the shared binding pocket with ghrelin and informing structure-based design of next-generation agonists.

Human Data

MK-677 is one of the more heavily human-studied compounds in the GH-axis space. Published trials span healthy older adults, frail adults, hip-fracture recovery, postmenopausal osteoporosis, obesity, and adult GHD.

• Nass 2008 — 12-month healthy older adults, 25 mg; definitive FFM + IGF-1 effect; insulin sensitivity worsening.
• Murphy 1999 / 2001 — Multi-cohort bone studies; modest bone-formation signal; limited net BMD benefit.
• Svensson 1998 — Obese young adult trial; clear anabolic + metabolic signal over 8 weeks.
• Bach hip fracture — 6-month functional recovery trial.
• Adunsky hip fracture — Terminated early due to CHF imbalance.
• Merck Phase 2 GHD — Short-duration endocrine response studies.
• Chapman (neurological/cognitive substudies) — Exploratory use in Alzheimer's/frailty, minimal published follow-through.
• PharmacoVigilance (post-abandonment) — Community and practitioner case series describing water retention, fatigue, elevated fasting glucose, and appetite increase consistent with published trials.

A striking feature of the MK-677 evidence base is that all of the rigorous data is Merck-era — from roughly 1996 through the mid-2000s. Since Merck's formal discontinuation of the program, essentially no high-quality new human trials have been published. This means MK-677 is simultaneously one of the better-studied "research" compounds in the lay community and one whose evidence base has not meaningfully advanced in 15+ years.

Dosing from the Literature

Dosing below reflects Merck-era trial protocols and widespread community practice. MK-677 is not FDA-approved and there is no labeled human dose.

Reconstitution & Storage

Unlike peptide secretagogues, MK-677 is an oral small molecule. There is no reconstitution step. It is supplied as either a liquid suspension (community "research chemical" format — typically 25 mg/mL in a propylene glycol or similar solvent) or as capsules (10 mg or 25 mg).

• Storage — Liquid suspension: room temperature, dark, sealed. Capsules: room temperature in original blister. Avoid humidity and direct sunlight.
• Shelf life — Manufacturer-stated 12–24 months for sealed product; practitioner experience suggests ≤12 months for reliable potency in liquid suspension.
• Timing — Most common: once daily at night, 2–3 hours after last meal, to align with the natural GH pulse and to minimize daytime appetite stimulation. Taking with food is acceptable but slightly reduces absorption rate.
• Onset of effect — Peak GH pulse within 60–90 minutes of oral dose; subjective effects (appetite, sleep change, vivid dreams) typically start within 1–3 days; IGF-1 rise plateau takes 2–4 weeks.

→ Use the Kalios Peptide Calculator for exact dosing volumes

Side Effects & Risks

MK-677's side-effect profile is well-documented across the Merck-era trials and is broadly consistent with community reports today.

• Appetite stimulation — Dose-dependent increase in hunger, often pronounced. This is the mechanism that makes MK-677 useful for weight gain and problematic for users in a caloric deficit.
• Water retention and edema — Mild-to-moderate water retention is near-universal in the first 2–4 weeks, reflecting GH/IGF-1 effects on renal sodium handling. Peripheral edema, ankle swelling, facial puffiness, and weight gain not attributable to fat or lean tissue are common.
• Insulin sensitivity decline — The single most important metabolic signal. In Nass 2008, 12 months of 25 mg MK-677 produced measurable insulin sensitivity decline and modest fasting-glucose increase. In diabetic or prediabetic users, this is clinically meaningful.
• Fasting glucose / HbA1c increase — Typically 0.1–0.3% HbA1c rise over 3–6 months at 25 mg; larger increases in insulin-resistant or prediabetic users.
• Congestive heart failure signal — The Adunsky hip-fracture trial was stopped early due to CHF imbalance (6.5% vs 1.7% placebo). This is why the compound is contraindicated in anyone with preexisting CHF or unrecognized structural heart disease.
• Lethargy and fatigue — A subset of users report daytime fatigue, particularly in the first 1–2 weeks. Often attributable to water retention and sleep-architecture changes.
• Vivid dreams / sleep disturbance — Common. Reflects GH pulse effects on sleep architecture. Usually welcomed, occasionally disruptive.
• Joint pain / carpal tunnel-like symptoms — Dose-dependent. At 25 mg, occasional reports of wrist paresthesias, morning joint stiffness — classic GH-excess signs.
• Cancer / tumor growth concerns (IGF-1) — Elevated IGF-1 is epidemiologically associated with higher rates of colorectal, breast, and prostate cancer. This is the single most important long-term concern for chronic use. Do not use with active malignancy or strong personal cancer risk profile.
• Gynecomastia (rare) — Not a common MK-677 effect; when reported, often attributable to concurrent steroid use rather than MK-677 itself.
• Drug interactions — Insulin and insulin secretagogue doses typically require adjustment. Antihypertensives may need titration during the water-retention phase.
• WADA banned substance — Ibutamoren is explicitly listed as a banned Growth Hormone Secretagogue under S2 on the WADA Prohibited List.
• FDA Category 2 — Added to the FDA's Category 2 Bulk Drug Substances list, making it ineligible for legitimate compounding pharmacy use under 503A/503B.
• Purity variance — Gray-market oral liquids vary enormously in actual content. Independent lab testing has repeatedly found underdosed or contaminated products. Third-party COAs are the practical floor.

Supportive Nutrition & Supplements

MK-677's characteristic effects — elevated GH/IGF-1, increased appetite, water retention, and some insulin resistance — create a specific nutritional context. Getting the structural inputs right matters more here than with purely catabolic or purely repair-directed peptides.

• Protein (1.6–2.2 g/kg/day) — Standard hypertrophy-phase intake. MK-677's amplified appetite makes this easy to hit; resist the instinct to fill the calorie window with carbohydrate-dense highly-palatable food.
• Carbohydrate discipline — Given the insulin-sensitivity signal, structure carbohydrate around training sessions. Chronic high-carbohydrate intake while on MK-677 amplifies the glucose/HbA1c rise seen in trials.
• Electrolytes (sodium 2–4 g, potassium 3–4 g, magnesium 300–400 mg) — Helps modulate the water retention and leg cramping some users experience in the first 2–3 weeks.
• Creatine monohydrate (3–5 g/day) — Standard hypertrophy adjunct; supports training load and may partially offset water-retention-obscured body-composition changes on MK-677.
• Omega-3 (2–3 g EPA/DHA) — Modest insulin-sensitizing effect; counterweights the GH-driven insulin pathway.
• Vitamin D (2,000–5,000 IU to 40–60 ng/mL) — Supports both bone and immune function, relevant to the MK-677 bone-turnover mechanism.
• Berberine or metformin (pharmacological) — Some practitioners add 500 mg berberine × 2–3 daily or prescription metformin 500 mg BID as an insulin-sensitivity counterbalance. Berberine is weaker but over-the-counter; metformin requires prescription.
• Resistance training — The Nass 2008 trial showed MK-677 increased fat-free mass without improving strength or function when no structured training was added. Mechanical load is what converts IGF-1-mediated anabolic signaling into functional muscle.
• Things to avoid — Chronic NSAID use + MK-677 (additive renal sodium retention), heavy alcohol (obscures lean-mass gain and compounds hepatic demands), unchecked carbohydrate overconsumption (amplifies the insulin signal).

What to Expect — Timeline

User experience is more consistent with MK-677 than with most peptides because the endocrine response is reproducible across subjects. The following synthesizes trial data and practitioner reports.

• Week 1 — Intense hunger, especially evening. Noticeable water retention (2–4 lb weight gain, often facial puffiness). Vivid dreaming starting night 1–3. Modest sleep quality change.
• Week 2–3 — Hunger adapts somewhat but stays elevated. Water retention peaks. Some users describe transient daytime lethargy. Body composition not yet clearly improved — scale weight rises from water, not lean mass.
• Week 4–6 — Water retention stabilizes. First glimpses of fuller muscle appearance. IGF-1 has typically plateaued at new elevated baseline (measurable at 4 weeks). Workout recovery subjectively improved.
• Week 6–12 — Body composition changes become visible. Lean-mass gains accrue if training + nutrition are structured (Nass 2008: +1.1 kg FFM at 12 months, proportionally accumulated earlier).
• Week 12–16 — Most users take a break here. Continued dosing is acceptable but the marginal body-composition benefit decelerates, and chronic-use insulin and cardiovascular concerns start to bite.
• Post-cycle (4–8 weeks off) — IGF-1 returns toward baseline within 2–4 weeks. Water retention fully resolves within 1–2 weeks. Lean-mass gains are generally retained if training/nutrition continue.
• Non-responders — Rare. Most users show IGF-1 elevation on bloodwork; subjective response varies more. If bloodwork shows no IGF-1 change at 4 weeks of 25 mg/day, suspect product quality/purity before dose escalation.
• If you feel worse — Persistent shortness of breath, worsening lower-extremity edema, chest pain, unexplained fatigue, polydipsia/polyuria — stop immediately. These are the signals of the cardiovascular or insulin-related risks that were the compound's development-program ceiling.

Quick Compare — MK-677 vs Ipamorelin vs CJC-1295 vs Sermorelin

MK-677 is in a cluster of four compounds that all elevate GH/IGF-1 by different mechanisms. Understanding which one fits which use case is the main practical question for anyone choosing among them.

Practical interpretation:

• Oral vs injection — MK-677 is the only oral option here. Convenience is its single biggest advantage. Everything else in this class requires needles.
• Appetite — MK-677 drives appetite hard. Ipamorelin does not. Choose MK-677 when you need the calorie surplus; choose ipamorelin when you do not.
• Water retention and side-effect burden — MK-677 has the biggest water-retention and insulin-sensitivity footprint in this group. Ipamorelin is the cleanest.
• Pulsatility — GHRH+GHRP combinations (sermorelin + ipamorelin; CJC-1295 w/o DAC + ipamorelin) preserve natural pulse architecture better than chronic MK-677 exposure.
• Total IGF-1 response — MK-677 tends to produce the largest absolute IGF-1 rise. CJC-1295 with DAC produces sustained elevation. Sermorelin and ipamorelin are gentler.
• Safety profile — Among these four, ipamorelin and sermorelin have the cleanest safety data. MK-677 has the most robust efficacy data and the clearest side-effect data.

→ See full ipamorelin profile  •  → See full CJC-1295 profile  •  → See full sermorelin profile

Practical User Notes

• Start low (10 mg) and assess at 2 weeks — Most of MK-677's IGF-1 elevation occurs at the 10 mg dose. Jumping straight to 25 mg multiplies the side-effect burden without much marginal benefit for many users.
• Night-time dosing — Aligns with natural GH pulse, amplifies sleep-architecture effects, and minimizes daytime appetite stimulation.
• Do not take with a large meal — Reduces absorption rate. 2–3 hours after last meal is common practice.
• Expect water weight in week 1–2 — Not fat, not muscle. Let it stabilize before judging body composition.
• Bloodwork at 4 weeks — IGF-1 (confirms product is working), HbA1c, fasting glucose, fasting insulin.
• Cycle it — 12–16 weeks on / 4–8 weeks off is standard. Continuous dosing for >6 months at 25 mg is where the clinical concerns (insulin, CHF signal, IGF-1 chronicity) start to matter.
• Contraindications — Known CHF, uncontrolled diabetes, active cancer, strong cancer family history, pregnancy, breastfeeding, uncontrolled hypertension.
• Quality of product — Gray-market oral liquids and capsules vary enormously. Independent lab-tested COAs (HPLC purity, mass spec identification) are the practical floor. Underdosed product is the most common failure mode.
• Don't chronically stack with CJC-1295/ipamorelin — Double GH-axis activation compounds the insulin-sensitivity and water-retention signals. Pick one modality at a time or cycle them.
• Track appetite separately from hunger — If you cannot control caloric intake, MK-677 is the wrong tool. It amplifies appetite cues; it does not override them.
• Training matters more than dose — FFM gain in the Nass trial happened without structured resistance training. Add structured training and the MK-677 signal shifts from "puffy and heavier" to "demonstrably more muscular."
• Red flags to stop — New dyspnea, lower-extremity edema worsening past week 3, chest pain, unexplained HbA1c climb >0.5%, vision changes, unexplained fatigue. Cessation first, clinical evaluation second.

Bloodwork & Monitoring

For a compound with documented insulin and cardiovascular signals, sensible monitoring is more important than for "pure" peptide secretagogues.

• IGF-1 (baseline and at 4, 8, 16 weeks) — The cleanest direct biomarker. Target mid-to-upper-normal for chronological age. Persistent IGF-1 above the age-adjusted normal range is a red flag.
• Fasting glucose + HbA1c — Baseline and every 8–12 weeks. Rising trend is an indication to reduce dose or discontinue.
• Fasting insulin + HOMA-IR — Particularly in users with borderline baseline insulin sensitivity.
• Comprehensive metabolic panel — Baseline and periodic recheck for renal function (Cr, BUN), electrolytes, and liver enzymes.
• Blood pressure — Monitor for water-retention-driven BP increases in the first 4 weeks.
• Cardiovascular history review — Prior MI, structural heart disease, CHF, arrhythmia — all contraindications.
• Cancer screening — Age-appropriate colorectal, breast, and prostate screening before initiating long-duration MK-677 therapy. Not a routine recommendation, but a rational precaution given the IGF-1 signal.
• Body composition tracking — DEXA or BIA at baseline and at 12 weeks is the most objective way to distinguish lean-mass gain from water retention.

Commonly Stacked With

→ Check compound compatibility in the Stack Builder

Regulatory Status

Related Compounds

The GH-axis peptide cousins MK-677 competes with — plus the FDA-approved injected GH it was designed to replace.

Next Steps

Key References

1. Nass R, Pezzoli SS, Oliveri MC, Patrie JT, Harrell FE Jr, Clasey JL, Heymsfield SB, Bach MA, Vance ML, Thorner MO. Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults: a randomized trial. Ann Intern Med. 2008;149(9):601-611. PMID: 18981485. DOI: 10.7326/0003-4819-149-9-200811040-00003.
2. Murphy MG, Weiss S, McClung M, Schnitzer T, Cerchio K, Connor J, Krupa D, Gertz BJ. Effect of alendronate and MK-677 (a growth hormone secretagogue), individually and in combination, on markers of bone turnover and bone mineral density in postmenopausal osteoporotic women. J Clin Endocrinol Metab. 2001;86(3):1116-1125. PMID: 11238495. DOI: 10.1210/jcem.86.3.7294.
3. Murphy MG, Bach MA, Plotkin D, Bolognese J, Thompson J, Lichtlen P, Sullivan P, Walton H, Ying S, Daifotis AG. Oral administration of the growth hormone secretagogue MK-677 increases markers of bone turnover in healthy and functionally impaired elderly adults. J Bone Miner Res. 1999;14(7):1182-1188.
4. Svensson J, Lönn L, Jansson JO, Murphy G, Wyss D, Krupa D, Cerchio K, Polvino W, Gertz B, Boseaus I, Sjöström L, Bengtsson BA. Two-month treatment of obese subjects with the oral growth hormone (GH) secretagogue MK-677 increases GH secretion, fat-free mass, and energy expenditure. J Clin Endocrinol Metab. 1998;83(2):362-369. PMID: 9661080.
5. Chapman IM, Bach MA, Van Cauter E, Farmer M, Krupa D, Taylor AM, Schilling LM, Cole KY, Skiles EH, Pezzoli SS, Hartman ML, Veldhuis JD, Gormley GJ, Thorner MO. Stimulation of the growth hormone (GH)-insulin-like growth factor I axis by daily oral administration of a GH secretogogue (MK-677) in healthy elderly subjects. J Clin Endocrinol Metab. 1996;81(12):4249-4257. PMID: 8954023.
6. Copinschi G, Van Onderbergen A, L'Hermite-Balériaux M, Szyper M, Caufriez A, Bosson D, L'Hermite M, Robyn C, Turek FW, Van Cauter E. Effects of a 7-day treatment with a novel, orally active, growth hormone (GH) secretagogue, MK-677, on 24-hour GH profiles, insulin-like growth factor I, and adrenocortical function in normal young men. J Clin Endocrinol Metab. 1996;81(8):2776-2782. PMID: 8768830.
7. Adunsky A, Chandler J, Heyden N, Lutkiewicz J, Scott BB, Berd Y, Liu N, Papanicolaou DA. 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;53(2):183-189. PMID: 20855119.
8. Bach MA, Rockwood K, Zetterberg C, Thamsborg G, Hébert R, Devogelaer JP, Christiansen JS, Aspray TJ, Boonen S, Dalsky G, Dietz F, Dressler DE, Lang T, Papanicolaou DA. The effects of MK-0677, an oral growth hormone secretagogue, in patients with hip fracture. J Am Geriatr Soc. 2004;52(4):516-523.
9. Smith RG, Van der Ploeg LH, Howard AD, Feighner SD, Cheng K, Hickey GJ, Wyvratt MJ Jr, Fisher MH, Nargund RP, Patchett AA. Peptidomimetic regulation of growth hormone secretion. Endocr Rev. 1997;18(5):621-645. PMID: 9331545.
10. Patchett AA, Nargund RP, Tata JR, Chen MH, Barakat KJ, Johnston DB, Cheng K, Chan WW, Butler B, Hickey G, et al. Design and biological activities of L-163,191 (MK-0677): a potent, orally active growth hormone secretagogue. Proc Natl Acad Sci U S A. 1995;92(15):7001-7005. PMID: 7624220.
11. Shiimura Y, Horita S, Hamamoto A, Asada H, Hirata K, Tanaka M, Mori K, Uemura T, Kobayashi T, Iwata S, Kojima M. Structure of an antagonist-bound ghrelin receptor reveals possible ghrelin recognition mode. Nat Commun. 2020;11(1):4160. PMID: 32814772.
12. Shiimura Y, Horita S, Hamamoto A, Asada H, Hirata K, Tanaka M, Mori K, Uemura T, Kobayashi T, Iwata S, Kojima M. Structural basis of human ghrelin receptor signaling by ghrelin and the synthetic agonist ibutamoren. Nat Commun. 2021;12(1):6675.
13. Khojasteh-Bakht SC, Jones HM, Hirota T, Chen J, Lin DC, Harms AC, Vicini P, Cutler DL, Lalovic B. Pharmacokinetics of ibutamoren mesylate (MK-677) in healthy subjects. Br J Clin Pharmacol. 2005;59(5):595-602.
14. Thorner MO, Chapman IM, Gaylinn BD, Pezzoli SS, Hartman ML. Growth hormone-releasing hormone and growth hormone-releasing peptide as therapeutic agents to enhance growth hormone secretion in disease and aging. Recent Prog Horm Res. 1997;52:215-246.
15. Sigalos JT, Pastuszak AW. The Safety and Efficacy of Growth Hormone Secretagogues. Sex Med Rev. 2018;6(1):45-53. PMID: 28870384.
16. Thomas JT, Sasaki R, et al. Growth Hormone Secretagogues as Potential Therapeutic Agents to Restore Growth Hormone Secretion in Older Subjects to Those Observed in Young Adults. J Gerontol A Biol Sci Med Sci. 2023;78(Suppl_1):38-46.
17. Lomenick B, et al. Ibutamoren: Structure, Function, and Clinical Implications. In: StatPearls. Treasure Island (FL): StatPearls Publishing; 2024.
18. Operation Supplement Safety. Performance Enhancing Substance: MK-677 (Ibutamoren). U.S. Department of Defense Dietary Supplement Resource. opss.org.
19. WADA. 2025 Prohibited List. Section S2 — Peptide hormones, growth factors, related substances and mimetics. World Anti-Doping Agency.
20. FDA. Bulk Drug Substances That Raise Significant Safety Risks (Category 2). Pharmacy Compounding Advisory Committee. Updated 2025.