MK-677 (Ibutamoren)

MK-677 (ibutamoren) is an oral compound that mimics ghrelin, the "hunger hormone," at its receptor and prompts the pituitary gland to release the body's own growth hormone (GH). Developed by Merck in the 1990s, it does what it is marketed to do: in randomized human trials it raised GH and IGF-1 reliably, for as long as two years of daily dosing (Ann Intern Med 2008).

That is precisely what makes MK-677 unusual on this site, and what makes its story worth reading carefully. It is a clinical-stage, abandoned compound: one of the most-studied GH secretagogues in humans, tested in hundreds of trial participants across aging, dieting, hip-fracture recovery, and Alzheimer's disease — and it still failed to become a medicine. The Alzheimer's trial was negative despite a 72.9% rise in IGF-1 (Neurology 2008), and the hip-fracture trial was stopped early after more heart-failure events in the treated group (Arch Gerontol Geriatr 2011). The same human data that proves the hormonal effect is the reason the risk signals — rising blood glucose, falling insulin sensitivity, edema, ravenous appetite — are so well documented.

One point of chemistry worth stating plainly: despite being sold on peptide and SARM sites, MK-677 is not a peptide. It is a non-peptide small molecule (a spiropiperidine derivative) engineered specifically so it could be swallowed instead of injected.

MK-677 is an agonist of the growth hormone secretagogue receptor (GHS-R1a) — the same receptor activated by ghrelin and by injectable secretagogue peptides such as ipamorelin and GHRP-6. Activating this receptor in the hypothalamus and pituitary amplifies the body's own pulsatile GH release rather than supplying external GH the way recombinant somatropin does.

• In healthy older adults, 25 mg daily increased mean 24-hour GH concentration by roughly 97% within two weeks, dose-dependently across 2, 10, and 25 mg doses (J Clin Endocrinol Metab 1996).

• IGF-1 — the hormone that mediates much of GH's growth effect — rose from a baseline of 141 µg/L to 265 µg/L after four weeks at 25 mg, reaching the normal range of young adults.

• Because MK-677 is long-acting, a single daily oral dose sustains the effect around the clock; in the two-year Nass trial, GH and IGF-1 remained elevated to young-adult levels throughout dosing (Ann Intern Med 2008).

Ghrelin-receptor activation also explains the compound's two most predictable non-GH effects: strong appetite stimulation and changes in sleep architecture.

MK-677 has no approved indication anywhere. Merck and academic collaborators ran it through an unusually broad clinical program, and each arm ended without a path to approval:

• Healthy aging / sarcopenia: a 2-year NIH-supported trial in 65 healthy adults aged 60–81 restored GH and IGF-1 to young-adult levels and added about 1.1 kg of fat-free mass, but did not improve strength or function, and raised fasting glucose (Ann Intern Med 2008).

• Catabolic states: in a short crossover study of healthy volunteers on a calorie-restricted diet, 25 mg daily flipped nitrogen balance from negative to positive — a genuine anti-catabolic signal, but in an 8-person, 7-day model (J Clin Endocrinol Metab 1998).

• Hip-fracture recovery: a phase IIb trial in 123 elderly patients (62 on MK-677, 61 on placebo) was terminated early over a congestive heart failure safety signal in a limited number of patients; the authors judged the safety profile unfavorable (Arch Gerontol Geriatr 2011).

• Alzheimer's disease: a 563-patient, 12-month randomized trial found no effect on any cognitive or functional endpoint despite clear IGF-1 target engagement (Neurology 2008).

Today MK-677 exists only as a gray-market product. The FDA has issued warning letters to sellers marketing "MK-677 Ibutamoren" alongside SARMs, classifying the products as unapproved new drugs and misbranded (FDA warning letter, 2023). It is not a lawful dietary-supplement ingredient.

Ibutamoren is named explicitly on the WADA Prohibited List as "ibutamoren (MK-677)," in the S2.2.4 growth hormone secretagogue bullet alongside anamorelin, capromorelin, ipamorelin, lenomorelin (ghrelin), macimorelin and tabimorelin. It is a non-Specified Substance, prohibited in and out of competition, with a four-year default sanction.

Because it is sold openly through "research chemical" and supplement channels, it reaches athletes who never intended to dope:

• Yoel Romero (UFC), six months. Ibutamoren was found in an out-of-competition sample collected 16 December 2015. At USADA's request the WADA-accredited laboratory in Salt Lake City analysed an unopened container of the supplement he had used and confirmed it was contaminated with ibutamoren, which was not on the label. That evidence reduced what could have been a two-year sanction to six months, and the product was added to USADA's high-risk supplement list (USADA announcement).

• Tristan Thompson (NBA), 25 games. The Cleveland Cavaliers centre was suspended on 23 January 2024 after testing positive for ibutamoren and the SARM LGD-4033 (ESPN, 23 January 2024).

The Romero case is the one worth reading closely. Proving contamination did not make the violation go away — it only shortened the sanction, and only because a sealed sample of the exact product still existed to be tested. Tested athletes should treat any product listing MK-677, ibutamoren, or "nutrobal" as a guaranteed positive-test risk.

Because MK-677 reached late-stage human trials, its side-effect profile is far better documented than that of most compounds in this catalog — and the documented profile is exactly why development stopped.

• Metabolic effects (the central concern): in the 2-year trial in older adults, fasting glucose rose by about 0.3 mmol/L (roughly 5 mg/dL) and insulin sensitivity declined (Ann Intern Med 2008). In obese men treated for 8 weeks, oral glucose tolerance was impaired at both 2 and 8 weeks (J Clin Endocrinol Metab 1998). This matters most for anyone with prediabetes, diabetes, or a family history of either.

• Cardiac signal in frail patients: the hip-fracture trial was stopped early over a congestive heart failure safety signal in elderly patients (Arch Gerontol Geriatr 2011). Whether this generalizes to young, healthy users is unknown — the point is that GH excess plus fluid retention is not benign in vulnerable hearts.

• Predictable GH/ghrelin effects: increased appetite (often marked), fluid retention and puffiness or edema, transient muscle or joint aches, and lethargy were the common complaints across trials.

Long-term questions remain open by definition: no trial has followed years of continuous use in healthy people, and sustained IGF-1 elevation carries theoretical concerns about promoting the growth of existing malignancies. Unregulated sourcing adds its own risks of mislabeled dose and identity.

MK-677's defining pharmacological feature is oral, once-daily activity. Unlike injectable secretagogues that produce a brief GH pulse, a single daily dose sustains elevated 24-hour GH and IGF-1, which is why every major trial used a simple once-daily schedule.

Two pharmacology points from the trials are worth knowing. First, effects on glucose appeared at the same doses that raised GH — there is no documented dose that separates the benefit from the metabolic cost. Second, IGF-1 elevation persisted throughout 12+ months of continuous dosing in the Nass trial, so "cycling" folklore should not be mistaken for evidence that intermittent use avoids the known risks.

MK-677 is sold as capsules, tablets, powders, or flavored liquids — never as a lyophilized injectable, since oral bioavailability is its entire reason for existing. It is most commonly stocked by vendors that also sell SARMs such as LGD-4033 or RAD-140, and marketing often lumps it in with them; chemically and mechanistically it is neither a SARM nor a steroid, and it has no androgen receptor activity.

In bodybuilding discourse it is frequently combined with injectable secretagogues or SARMs. No controlled human data exists for any such combination, and the FDA's warning letters cover exactly this product category (FDA, 2023).

The MK-677 literature follows a consistent arc: hormone endpoints succeed, clinical endpoints fail.

• Hormones: dose-dependent GH increases and normalization of age-related IGF-1 decline in 32 elderly subjects (JCEM 1996); sustained over 2 years in 65 older adults (Ann Intern Med 2008).

• Body composition: about 1.1 kg fat-free mass gained vs placebo at 12 months (Nass); fat-free mass up but total and visceral fat unchanged after 8 weeks in obese men (JCEM 1998).

• Anti-catabolism: reversed nitrogen loss during caloric restriction in 8 volunteers (JCEM 1998).

• Sleep: improved sleep-quality measures, including a near-50% REM increase in older subjects in a small polysomnography study (Neuroendocrinology 1997).

• Bone: increased markers of both bone formation and resorption in 187 elderly adults — turnover, not proven fracture protection (J Bone Miner Res 1999).

• Clinical outcomes: negative in Alzheimer's disease (n=563, Neurology 2008) and stopped for safety in hip-fracture recovery (n=123, Arch Gerontol Geriatr 2011).

For a deeper walkthrough of these trials, see the MK-677 research and evidence overview.

For deeper dives on this compound, see:

• MK-677 benefits and areas of interest
• MK-677 side effects and safety context
• MK-677 dosing in published trials (educational)
• MK-677 research and evidence overview

Is MK-677 a peptide? No. It is a non-peptide small molecule (a spiropiperidine derivative) designed to survive digestion and work as an oral pill. It gets grouped with peptides because it activates the same ghrelin receptor as injectable secretagogues like ipamorelin and GHRP-6 — the target is shared, the chemistry is not.

Is MK-677 a SARM or a steroid? Neither. It has no androgen receptor activity and no steroid structure. The confusion comes from commerce: it is overwhelmingly sold by the same vendors, and in the same "stacks," as SARMs — a pairing the FDA has targeted in warning letters covering products marketed as "MK-677 Ibutamoren" (FDA, 2023).

Does MK-677 really increase growth hormone? Yes — this is one of the best-established facts about it. In randomized trials, 25 mg daily roughly doubled 24-hour GH concentrations within two weeks and raised IGF-1 into the young-adult range (JCEM 1996), with the effect sustained over two years of dosing (Ann Intern Med 2008). Raising GH is not the same as producing the muscle, fat-loss, or anti-aging outcomes it is marketed for — those endpoints were never demonstrated.

Is MK-677 legal or FDA-approved? It is not an approved drug anywhere, and it is not a lawful dietary-supplement ingredient. Products sold for human consumption are unapproved new drugs in the FDA's framing. Possession is not generally criminalized in the US the way controlled substances are, but selling it for human use is illegal, and quality of gray-market material is unverified.

Does MK-677 raise blood sugar? Yes, measurably. Fasting glucose rose and insulin sensitivity fell in the two-year older-adult trial (Ann Intern Med 2008), and glucose tolerance was impaired within two weeks in obese men (JCEM 1998). This is the most consistent adverse finding in the entire literature.

Is MK-677 banned in sports? Yes. Ibutamoren is named on the WADA Prohibited List under S2 as a growth hormone secretagogue, prohibited at all times, in and out of competition.

Why did MK-677 never become a medicine? Not for lack of testing. The Alzheimer's trial showed no clinical benefit despite raising IGF-1 by 72.9% (Neurology 2008), and the hip-fracture trial was stopped early over heart-failure events (Arch Gerontol Geriatr 2011). No studied population showed a risk–benefit balance worth approving.