Ibutamoren
Also sold as: MK-677, MK-0677, Ibutamoren Mesylate, L-163,191, Oratrope
Ibutamoren (MK-677) is not approved by FDA, which states that its safety and efficacy have not been established; FDA has determined that it is excluded from the definition of a dietary supplement; and FDA has placed ibutamoren mesylate in Category 2 of its 503A bulk drug substances list — substances that raise significant safety risks — over the potential for congestive heart failure. It does have real human trial data, and that data is largely negative: in a 2008 two-year placebo-controlled trial of 65 healthy adults aged 60 to 81, researchers reported that fat-free mass increased but that the gain produced no change in strength or function, while fasting glucose rose and insulin sensitivity decreased.
Which molecule this is. Not a peptide, despite being sold throughout the research-peptide market and routinely catalogued alongside GHRPs. Ibutamoren is an orally active non-peptide spiropiperidine — a ghrelin-receptor (GHS-R1a) agonist that acts as a growth hormone secretagogue. This distinction is not pedantry: FDA's Category 2 rationale for the surrounding peptides (ipamorelin, GHRP-2, GHRP-6, kisspeptin-10) turns on immunogenicity and peptide-related impurities. Ibutamoren's does not. Its listed risk is pharmacological, and it is cardiac. FDA lists the mesylate salt, which is the form nominated and the form sold.
FDA status
FDA has not approved this and it is not in active development toward approval. That says nothing about whether it is being sold — most substances in this category are.
Not an FDA-approved drug for any indication, and not in active development toward approval. That says nothing about whether it is sold — it is.
503A compounding
FDA has identified significant safety risks with this substance.
Present by name, as 'Ibutamoren Mesylate', in Category 2 of the list updated 2026-05-14 — verified by fetching and text-extracting the document directly. Category 2 contains exactly six substances: Cesium Chloride, Domperidone, Germanium Sesquioxide, Ibutamoren Mesylate, Kisspeptin-10, and Quinacrine Hydrochloride for intrauterine administration. Ibutamoren is therefore one of the few compounds in this corpus whose Category 2 status is current fact rather than a stale claim about a withdrawn nomination. It is also listed under 503B (designated 2022-12-29). Category 2 is not the criminal line either: the Watkins indictment (D. Utah, 1:26-cr-00015, 2026-04-01) charges misbranding under 352(b), which is why Category 1 substances appear in the same indictment as Category 2 and unlisted ones. Sourcing and labeling are the line.
Evidence
There is human data, but efficacy is not established. This includes programmes that were tested and failed.
Administration check run per-study, not inferred from counts. Both trials below were opened and confirmed to have ADMINISTERED ibutamoren orally to human participants — neither measures an endogenous analyte as a biomarker, so the trap that voids the apparent human evidence for MOTS-c and TB-500 does not apply. In a 2008 two-year double-blind placebo-controlled modified-crossover trial of 65 healthy adults aged 60-81 (Nass et al., Ann Intern Med, PMID 18981485), researchers administered oral MK-677 or placebo daily and reported that GH and IGF-I rose into the young-adult range and mean fat-free mass increased by 1.1 kg versus a 0.5 kg decrease on placebo. The authors also reported that the fat-free mass gain did not translate into strength or function, that fasting glucose rose and insulin sensitivity decreased, that cortisol rose, and that limb fat increased more than on placebo. Limitations, stated by the authors: 'Study power (duration and participant number) was insufficient to evaluate functional end points in healthy elderly persons.' The scope-limiting phrase is the authors' own and is kept: they stated the limitation for the population they studied, not as a general claim about the drug. In a 2011 multicenter randomized placebo-controlled Phase IIb trial of 123 elderly hip fracture patients (Adunsky et al., Arch Gerontol Geriatr, PMID 21067829), researchers administered oral MK-0677 or placebo daily and reported that IGF-1 rose by 51.4 ng/ml while most functional performance measures did not improve; the trial was terminated early for a congestive heart failure signal, and the authors concluded an unfavorable safety profile in that population. The precise statement: real, adequately-blinded human administration data exists, and it is largely NEGATIVE on the outcomes people buy this compound for. Ibutamoren reliably raises GH and IGF-1 — that pharmacodynamic effect is well established and is not in dispute. What is not established is that the hormonal change produces clinical benefit: the two trials that looked for strength and function did not find it. 'Promising but unproven' here means tested and failed, not untested. No FDA approval for any indication was ever granted; Merck's development programme did not yield one. Separately, NCT05364684 (ibutamoren in nonalcoholic fatty liver disease) was checked and is a legitimate registration — Massachusetts General Hospital, Phase 2, started 2022-08-10, COMPLETED, results posted. It is unrelated to the eight-registration Hudson Biotech cluster contaminating this vertical. Its results were not read for this record, so no outcome is claimed from it and it is not relied on for the tier.
“Increased fat-free mass did not result in changes in strength or function.”Checked against the source on .
What FDA found
FDA’s own words. These are the most citable thing on this site, and the least likely to appear anywhere funded by someone selling the compound.
FDA placed ibutamoren mesylate in Category 2 — bulk drug substances that raise significant safety risks — for both 503A (2023-09-29) and 503B (2022-12-29) compounding, on the basis of a cardiac signal seen in a human trial.
Unlike the seven substances before PCAC on 23-24 July 2026, ibutamoren has no briefing document and is not on that agenda — its status is settled rather than pending, so there is no 'we propose not adding' language to quote and no advisory-committee outcome to await. Do not compress the category into the legal bar: these are two distinct facts, and an earlier draft of this note fused them into one causal claim ('Category 2 placement means it cannot be used in compounding'). It does not mean that. What bars lawful use is the baseline section 503A(b)(1)(A) requirement, which would bite identically on a Category 1 or an unlisted substance; Category 2 is the separate fact that FDA declines to extend its Category 1 enforcement forbearance. FDA's guidance says in terms that Category 2 substances 'may be eligible for inclusion on the 503A bulks list' — see the interim-policy finding below, which carries both mechanisms in FDA's own words. Note what FDA's rationale rests on: not an absence of data, but the presence of it. The trial FDA cites is Adunsky et al. 2011 (PMID 21067829), which is the same trial the market cites as evidence ibutamoren 'works' for recovery. It is the reason FDA calls it unsafe.
Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks — FDA, 29 September 2023“Ibutamoren mesylate poses significant safety risks due to the potential for congestive heart failure in certain patients. The agency is aware of a randomized, placebo-controlled trial assessing ibutamoren mesylate for the treatment of patients recovering from hip fracture that “was terminated early due to a potential safety signal of congestive heart failure.””
Checked against the source on .FDA states that ibutamoren is not an FDA-approved active ingredient and that its safety and efficacy have not been established, and that the long-term effects of ibutamoren use are unknown.
The flattest, most quotable statement of ibutamoren's approval status in FDA's own voice, and it is not in the bulks list — it is in a consumer health-fraud notification. Word-for-word identical language appears in the Agebox warning letter (MARCS-CMS 718252, 2025-12-19) — two documents, but one firm and one laboratory finding, so treat this as FDA saying it twice rather than as independent corroboration. An earlier draft of this note also cited the Musclepower Enterprise letter (MARCS-CMS 719339, 2025-12-12) for this language. That letter does not contain it: it carries the dietary-supplement exclusion determination and nothing about approval status or side effects. The citation was removed rather than softened. Read the finding against the record's own evidence note: 'not approved' and 'safety and efficacy have not been established' are true, and are NOT the same claim as 'untested'. Merck ran real placebo-controlled human trials. Nothing came of them. The middle of the ellipsis is FDA's adverse-effect enumeration, quoted in full in the finding below.
Agebox iKids Growth Day Formula may be harmful due to hidden ingredient — FDA, 23 September 2025“Ibutamoren (also known as MK-677) is an active ingredient not approved by FDA, and therefore its safety and efficacy have not been established. Ibutamoren is a growth hormone secretagogue that stimulates the release of growth hormone. ... Long-term effects of ibutamoren use are unknown and may pose additional health risks.”
Checked against the source on .FDA has determined that ibutamoren is excluded from the definition of a dietary supplement, because it was authorized for investigation as a new drug and substantial clinical investigations were instituted and made public before it was ever marketed as a supplement or food.
The most useful finding on this record for anyone reading a label, and the one with the sharpest irony in it. The drug-exclusion clause bites BECAUSE Merck did the clinical work: the very existence of the public IND is what forecloses the supplement route forever. A compound with no trials behind it would not be excluded on this ground. So the trials the market cites as proof ibutamoren works are, verbatim, FDA's stated reason it cannot lawfully be sold as a supplement. There is no combination of formulation, labeling or disclaimer that cures this — the exclusion attaches to the substance, not to the marketing.
Warning Letter — Agebox Inc., MARCS-CMS 718252 — FDA, 19 December 2025“Based on available evidence, ibutamoren has been authorized for investigation as a new drug, substantial clinical investigations of ibutamoren as a new drug have been instituted, and the existence of such investigations has been made public, and ibutamoren was not marketed as a dietary supplement or as a conventional food prior to such authorization. Therefore, FDA has determined that ibutamoren is excluded from the definition of a dietary supplement under section 201(ff)(3)(B)(ii) of the FD&C Act, 21 U.S.C. 321(ff)(3)(B)(ii).”
Checked against the source on .In a warning letter, FDA enumerated the adverse effects it associates with ibutamoren: increased appetite, water retention, fatigue, muscle pain, potential alterations in glucose metabolism and insulin sensitivity, and increased potential for congestive heart failure in certain individuals.
Notable for being broader than the Category 2 entry, which cites only the congestive heart failure signal. Here FDA independently names the glucose and insulin-sensitivity effects, the edema and the muscle pain — which is the full published adverse-event profile of the 2008 Nass trial (PMID 18981485), reassembled in FDA's voice without the trial's favorable body-composition result beside it. The context matters and is not incidental: FDA's laboratory analysis had found ibutamoren mesylate UNDECLARED in products sold for children aged five and older, so this list was written about children who were given the drug without anyone knowing.
Warning Letter — Agebox Inc., MARCS-CMS 718252 — FDA, 19 December 2025“Use of ibutamoren may cause serious side effects including increased appetite, water retention, fatigue, muscle pain, potential alterations in glucose metabolism and insulin sensitivity, and even may increase the potential for congestive heart failure in certain individuals.”
Checked against the source on .FDA's interim policy defines Category 2 as substances that were nominated with enough information to evaluate and that may still be eligible for the 503A bulks list, but for which FDA has identified significant safety risks in compounding — and for which it therefore does not intend to adopt the enforcement policy it applies to Category 1.
The finding that stops this record from saying something FDA did not say. Two mechanisms live in this guidance and they are constantly fused into one. Mechanism one, the statutory bar, which is what actually makes ibutamoren unusable: 'a bulk drug substance that is not the subject of an applicable USP or NF monograph or is not a component of an FDA-approved drug product cannot be used in compounding unless it appears on a list promulgated as a regulation ... A drug product compounded from a bulk drug substance that does not meet any of these three conditions is not eligible for the exemptions in section 503A and may violate the FD&C Act.' That bar does not care about categories. Mechanism two, the enforcement forbearance, which is what the category actually governs: FDA states it 'does not intend to take action against a State-licensed pharmacy, Federal facility, or licensed physician compounding a drug product using a bulk drug substance' meeting none of the three statutory conditions, but only 'if all of the following circumstances are present: (1) The bulk drug substance appears in 503A Category 1 on FDA's website'. Ibutamoren mesylate is in Category 2, so that forbearance is not extended to it. Read those together and the honest sentence is narrow: Category 2 does not make ibutamoren illegal to compound — the statutory bar already did that — it means FDA has not said it will refrain from acting against a compounder who uses it anyway. Note also what Category 2 does NOT mean, because the inverse error is just as common: FDA's own definition says these substances 'may be eligible for inclusion on the 503A bulks list'. Category 2 is a pending safety determination, not a permanent ban.
Interim Policy on Compounding Using Bulk Drug Substances Under Section 503A of the Federal Food, Drug, and Cosmetic Act — Guidance for Industry — FDA, 7 January 2025“503A Category 2 – Substances Nominated for the Bulks List That Raise Significant Safety Risks: These substances were nominated with sufficient supporting information to permit FDA to evaluate them, and they may be eligible for inclusion on the 503A bulks list. However, FDA has identified significant safety risks relating to the use of these substances in compounding pending further evaluation and, therefore, does not intend to adopt the policy described for the substances in Category 1.”
Checked against the source on .FDA lists ibutamoren mesylate in the table of substances currently in Category 2 — not in the separate list of substances previously in Category 2 whose nominations were withdrawn by the nominators.
A structural finding, and the one that separates ibutamoren from most of this corpus. FDA's page carries two distinct lists, and which list a substance is on is the whole question. BPC-157, MOTS-c, TB-500, epitalon, KPV, semax and the rest sit in the withdrawn list — their nominators walked away, and the market misreads that departure as FDA relenting. Ibutamoren mesylate sits in the live table, by name, with its designation dates in the adjacent column, verified against the list updated 2026-05-14. Nothing here moved sideways. Neither list is a route to lawful supply, but only one of them is a standing FDA safety determination, and ibutamoren is on it.
Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks — FDA, 29 September 2023“Bulk drug substances that may present significant safety risks have been placed in category 2 under the interim policies. ... Bulk drug substances nominated but withdrawn ... This list of bulk drug substances previously in category 2 of the interim policies were withdrawn by the nominators.”
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Documented safety signals
A randomized, double-blind, placebo-controlled Phase IIb trial of 123 elderly hip fracture patients was terminated early for a congestive heart failure signal. The authors concluded that MK-0677 has an unfavorable safety profile in this population, and that the rise in IGF-1 was not paralleled by improvement in most functional performance measures.
This is the trial FDA relies on for the Category 2 designation. An earlier draft of this entry reported the congestive-heart-failure events as a 4-of-62 versus 1-of-61 split. Those per-arm counts are not in the abstract this entry cites — the abstract says only 'a limited number of patients' — and the draft attributed them to unspecified 'secondary reporting' while citing PubMed. A number sourced to a document that does not contain it is the defect this site exists to correct, so the counts are removed rather than re-attributed to a source we have not read. What the abstract does carry, verbatim, is the termination, the unfavorable safety conclusion, and the arm sizes (n = 62 MK-0677, n = 61 placebo). The population was elderly hip fracture patients, who carry elevated baseline cardiac risk — this signal should not be silently generalized to healthy younger users, nor dismissed as irrelevant to them.
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, 1 September 2011“Trial was terminated early due to a safety signal of congestive heart failure in a limited number of patients.”
Checked against the source on .In the 2008 two-year trial in healthy older adults, researchers reported that fasting blood glucose rose an average of 0.3 mmol/L (5 mg/dL) and insulin sensitivity decreased in the MK-677 group, and that cortisol rose by 47 nmol/L.
Reported in the trial the market cites most often for the fat-free mass result. The same paper that supplies the favorable body-composition number also supplies the glucose, insulin-sensitivity and cortisol findings, and reports that the fat-free mass gain did not produce strength or function gains.
Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults: a randomized trial — Annals of Internal Medicine, 4 November 2008“Fasting blood glucose level increased an average of 0.3 mmol/L (5 mg/dL) in the MK-677 group (P = 0.015), and insulin sensitivity decreased.”
Checked against the source on .The most frequent side effects in the 2008 trial were an increase in appetite that subsided within a few months, and transient mild lower-extremity edema and muscle pain.
Edema is worth reading alongside the congestive heart failure signal from the hip fracture trial rather than in isolation, given fluid retention is a recognized consequence of raising GH/IGF-1. The two reports are consistent with one mechanism; that connection is ours and is not asserted by either paper or by FDA.
Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults: a randomized trial — Annals of Internal Medicine, 4 November 2008“The most frequent side effects were an increase in appetite that subsided in a few months and transient, mild lower-extremity edema and muscle pain.”
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Questions people actually ask
Every answer cites the document behind it. Where the honest answer is “nobody knows”, that is the answer you will get.
- Is MK-677 legal in 2026?
No, MK-677 (ibutamoren) has no lawful route to consumer sale in the United States. FDA has determined that ibutamoren is excluded from the definition of a dietary supplement under section 201(ff)(3)(B)(ii) of the Federal Food, Drug, and Cosmetic Act, so it cannot be sold as a supplement; it is not an FDA-approved drug; and FDA has told a firm selling an ibutamoren-containing product that its products are "unapproved new drugs introduced or delivered for introduction into interstate commerce in violation of sections 505(a) and 301(d) of the Federal Food, Drug, and Cosmetic Act." Note who that violation runs to: FDA addressed it to the seller, not to buyers.
Warning Letter — Agebox Inc., MARCS-CMS 718252 — FDA, 19 December 2025“As described below, these products are unapproved new drugs introduced or delivered for introduction into interstate commerce in violation of sections 505(a) and 301(d) of the Federal Food, Drug, and Cosmetic Act (FD&C Act), 21 U.S.C. 355(a) and 331(d).”
Checked against the source on .- Did FDA approve ibutamoren (MK-677)?
No. FDA has never approved ibutamoren (MK-677) for any indication or population. FDA states directly that ibutamoren "is an active ingredient not approved by FDA, and therefore its safety and efficacy have not been established" and that "long-term effects of ibutamoren use are unknown and may pose additional health risks." Ibutamoren was developed as an investigational drug and taken into human trials, but that development programme never produced an approval.
Agebox iKids Growth Day Formula may be harmful due to hidden ingredient — FDA, 23 September 2025Checked against the source on .- Is there any human evidence that MK-677 builds muscle?
There is real human trial evidence for MK-677 (ibutamoren), and it does not support a strength or function benefit. In a 2008 two-year randomized, double-blind, placebo-controlled trial of 65 healthy adults aged 60 to 81 (Nass et al., Annals of Internal Medicine, PMID 18981485), researchers administered oral MK-677 or placebo and reported that growth hormone and IGF-I rose into the young-adult range and mean fat-free mass increased by 1.1 kg versus a 0.5 kg decrease on placebo — but concluded that "increased fat-free mass did not result in changes in strength or function." The same trial reported that fasting glucose rose and insulin sensitivity decreased. MK-677 raises GH and IGF-1 reliably; that hormonal effect is well established. What the trials did not find is that the hormonal change delivers the outcome.
Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults: a randomized trial — Annals of Internal Medicine, 4 November 2008“Increased fat-free mass did not result in changes in strength or function.”
Checked against the source on .- Can I get MK-677 from a compounding pharmacy?
No. FDA placed ibutamoren mesylate (MK-677) in Category 2 of both the 503A list (September 29, 2023) and the 503B list (December 29, 2022) — bulk drug substances that raise significant safety risks — and it remains there on the list updated May 14, 2026. FDA's stated reason is that "ibutamoren mesylate poses significant safety risks due to the potential for congestive heart failure in certain patients," and that the agency "is aware of a randomized, placebo-controlled trial assessing ibutamoren mesylate for the treatment of patients recovering from hip fracture that 'was terminated early due to a potential safety signal of congestive heart failure.'" Ibutamoren is one of only six substances in 503A Category 2, alongside cesium chloride, domperidone, germanium sesquioxide, kisspeptin-10, and quinacrine hydrochloride for intrauterine administration.
Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks — FDA, 29 September 2023“Ibutamoren mesylate poses significant safety risks due to the potential for congestive heart failure in certain patients. The agency is aware of a randomized, placebo-controlled trial assessing ibutamoren mesylate for the treatment of patients recovering from hip fracture that “was terminated early due to a potential safety signal of congestive heart failure.””
Checked against the source on .- What does Category 2 actually mean — is it a ban?
No, Category 2 is not a ban, and it is not what makes MK-677 unavailable. Two separate things are at work in FDA's interim policy guidance. First, the statutory bar: FDA states that "a bulk drug substance that is not the subject of an applicable USP or NF monograph or is not a component of an FDA-approved drug product cannot be used in compounding unless it appears on a list promulgated as a regulation," and that a drug compounded from a substance meeting none of those three conditions "is not eligible for the exemptions in section 503A and may violate the FD&C Act." That bar applies regardless of category. Second, the enforcement policy: FDA says it does not intend to take action against a state-licensed pharmacy, federal facility, or licensed physician compounding with a nominated substance, but only "if all of the following circumstances are present: (1) The bulk drug substance appears in 503A Category 1 on FDA's website." Ibutamoren mesylate is in Category 2, so that forbearance does not extend to it. FDA defines Category 2 substances as ones that "may be eligible for inclusion on the 503A bulks list" but for which it "has identified significant safety risks relating to the use of these substances in compounding pending further evaluation." So Category 2 means FDA has not promised to refrain from acting against a compounder who uses it — not that the question is permanently closed.
Interim Policy on Compounding Using Bulk Drug Substances Under Section 503A of the Federal Food, Drug, and Cosmetic Act — Guidance for Industry — FDA, 7 January 2025“However, FDA has identified significant safety risks relating to the use of these substances in compounding pending further evaluation and, therefore, does not intend to adopt the policy described for the substances in Category 1. ... However, at this time, until a substance has been evaluated and is identified in a final rule as being included or not included on the 503A bulks list, FDA does not intend to take action against a State-licensed pharmacy, Federal facility, or licensed physician compounding a drug product using a bulk drug substance that is not a component of an FDA-approved drug product, the subject of an applicable USP or NF monograph, or on the 503A bulks list codified at 21 CFR 216.23(a), if all of the following circumstances are present: (1) The bulk drug substance appears in 503A Category 1 on FDA's website ...”
Checked against the source on .- Is MK-677 banned in sport?
Yes. MK-677 is named on the World Anti-Doping Agency's 2026 Prohibited List, which came into effect on 1 January 2026. It appears at S2.2.4 under growth hormone releasing factors, in the entry for "growth hormone secretagogues (GHS) and their mimetics [e.g. anamorelin, capromorelin, ibutamoren (MK-677), ipamorelin, lenomorelin (ghrelin), macimorelin and tabimorelin]." Class S2 is prohibited at all times — both in-competition and out-of-competition — and WADA states that all prohibited substances in the S2 class are non-Specified Substances.
World Anti-Doping Code International Standard: Prohibited List 2026 — World Anti-Doping Agency, 1 January 2026“growth hormone secretagogues (GHS) and their mimetics [e.g. anamorelin, capromorelin, ibutamoren (MK-677), ipamorelin, lenomorelin (ghrelin), macimorelin and tabimorelin]”
Checked against the source on .- Has ibutamoren been found in products that don't list it on the label?
Yes. FDA laboratory analysis confirmed that Agebox iKids Growth Day Formula — a product promoted and sold to stimulate growth in children ages five and older — contained ibutamoren that was not listed on the product label. FDA advised consumers not to purchase or use the product in a health fraud notification dated September 23, 2025, and issued a warning letter to Agebox Inc. on December 19, 2025 stating that the failure to disclose ibutamoren mesylate rendered the products misbranded under section 502(a) of the Federal Food, Drug, and Cosmetic Act. FDA also states that it is unable to test and identify all products marketed as dietary supplements that have potentially harmful hidden ingredients.
Agebox iKids Growth Day Formula may be harmful due to hidden ingredient — FDA, 23 September 2025“FDA laboratory analysis confirmed that Agebox iKids Growth Day Formula contains ibutamoren not listed on the product label.”
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