A reference work, not a recommendation to use: this profile describes mechanism and evidence and does not replace medical advice. The claims come from marketing and forums and are tested here, not endorsed. Manufacture, possession, trade or use may be prohibited; see “Legal status” for details.

Claims checked

  • More muscle mass and less fat

    Small benefit

    Muscle & performance · healthy (older adults) · Human, randomised small studiesEvery study behind this level and result had fewer than 100 participants. Small studies report larger effects on average than large ones, so the result is less certain.

    In the two-year study, lean mass rose by 1.1 kg (placebo −0.5 kg), abdominal and total fat remained unchanged, limb fat increased, and strength and function did not improve [8]. Similar in obesity: more lean mass, no fat loss [5]. Both studies are small (65 and 24 participants) [8][5].

  • Deeper sleep

    Single unconfirmed finding

    Sleep · healthy · Human, randomised small studiesEvery study behind this level and result had fewer than 100 participants. Small studies report larger effects on average than large ones, so the result is less certain.

    A placebo-controlled crossover study with eight young and six older people: about 50% more deep sleep (stage IV) in the younger participants and more REM sleep [7]. An independent replication was not found.

  • Strengthens the bones

    Mixed results

    Recovery & healing · healthy (young men with obesity) · Human, randomised small studiesEvery study behind this level and result had fewer than 100 participants. Small studies report larger effects on average than large ones, so the result is less certain.

    Markers of bone formation and bone resorption rose simultaneously, so turnover increased [6]; in the two-year study, bone density changed in line with increased turnover [8]. Both studies are small (24 and 65 participants) [6][8]. There are no data on fractures.

  • Protects the brain from Alzheimer's

    No benefit

    Cognition & focus · Patients: mild to moderate Alzheimer's disease · Human, randomised manufacturer-fundedAccording to their funding or competing-interest statements, all studies behind this result were paid for, wholly or in part, by the maker of the product or compound, or list employees of the maker among their authors. Manufacturer-funded studies on average come out more favourably for the product.

    RCT with 563 participants over twelve months: despite 60 to 73% higher IGF-1, no difference in any of the four endpoints [9]. According to the affiliation, the first author worked at Merck Research Laboratories; Merck supplied the study drug [9][8]. Prevention in healthy people has not been studied.

  • Speeds recovery after injuries

    No benefit

    Recovery & healing · Patients: older people after hip fracture · Human, randomised

    RCT with 123 participants: only gait speed was better, most functional tests were not; the study was stopped early because of cases of heart failure [10].

small studies: Every study behind this level and result had fewer than 100 participants. Small studies report larger effects on average than large ones, so the result is less certain.

manufacturer-funded: According to their funding or competing-interest statements, all studies behind this result were paid for, wholly or in part, by the maker of the product or compound, or list employees of the maker among their authors. Manufacturer-funded studies on average come out more favourably for the product.

Mechanism of action

Evidence map: MK-677

Each line stands for a published finding; line style and color show where it comes from. The filter hides weaker evidence levels. Sources: see references.

Unlike most agents in this group, MK-677 is not a peptide but a small molecule that works orally. It acts at the same receptor as the peptides GHRP-6 and hexarelin: the ghrelin receptor GHSR-1a in the pituitary and hypothalamus, which was cloned in 1996 as the common target of this class of compounds [1]. In the United States, MK-677 is not approved as a drug; the FDA places it, as a bulk substance for pharmacy compounding, in the category of substances with potential significant safety risks and refers to a heart failure signal [2]; in sport, growth hormone secretagogues are prohibited [3]. Pharmacologically, this class triggers a pulsatile release in which the body's own feedback via somatostatin and IGF-1 is preserved [3].

The early studies showed mainly hormonal effects. In eight healthy volunteers on caloric restriction, MK-677 turned the negative nitrogen balance positive, a sign of reduced protein breakdown [4]. In 24 otherwise healthy men with obesity, IGF-1 rose by about 40% over eight weeks and lean mass increased, but total and abdominal fat did not; basal metabolic rate was increased only temporarily, and the glucose tolerance test worsened after two and eight weeks [5]. In the same group, markers of bone formation and bone resorption rose simultaneously, so overall bone turnover increased [6]. A crossover study with eight young and six older people found longer deep sleep (stage IV, about 50% more in the younger participants) and more REM sleep under MK-677 [7].

The most informative study ran for two years: 65 healthy people between 60 and 81 years of age received MK-677 or placebo. Growth hormone and IGF-1 returned to the levels of young adults. Lean mass rose by 1.1 kg, while it fell by 0.5 kg under placebo; abdominal fat and total fat mass did not change, fat in the limbs increased more, and body weight rose by 2.7 kg versus 0.8 kg. Fasting blood glucose and insulin sensitivity worsened, cortisol rose, and common side effects were increased appetite, mild leg edema, and muscle pain. Crucially, strength and everyday function did not improve despite more lean mass [8].

In disease settings, the compound disappointed. In 563 people with mild to moderate Alzheimer's disease, IGF-1 rose by 60 to 73%, but the course of the disease did not change over twelve months in any of the four endpoints [9]. A study of 123 older people after hip fracture found a benefit only in gait speed, not in most other functional tests, and was stopped early because of cases of heart failure; the authors rate the safety profile in this group as unfavorable [10]. A review of growth hormone secretagogues notes that long-term data on cancer incidence and mortality are lacking and that reduced insulin sensitivity is the most important known disadvantage [11]. In the fitness scene, MK-677 is often combined with SARMs; a case report of a 25-year-old man on MK-677 and LGD-4033 describes sharply elevated liver enzymes, worsened blood lipids, and collapsed testosterone, which mostly returned after discontinuation [12].

Targets

TargetTypeActionKey dataEvidence
Ghrelin receptor GHSR-1aReceptorAgonistcommon target of the growth hormone secretagogues, cloned in 1996 Laboratory[1]
growth hormone–IGF-1 axisHormone axisActivatorIGF-1 raised by about 40% (obesity, 8 weeks) to 73% (Alzheimer's, 12 months); GH and IGF-1 in the range of young adults (healthy older people) Human, randomised[5][8][9]

Effect profile

Which signaling systems the compound affects according to current data. ↑ enhanced, ↓ dampened, ≈ modulated, ○ no effect; dots = evidence level.

  • Dopamineno data
  • Noradrenalineno data
  • Serotoninno data
  • Acetylcholineno data
  • Glutamate · AMPAno data
  • Glutamate · NMDAno data
  • GABAno data
  • Histamineno data
  • Orexinno data
  • Adenosineno data
  • Opioidsno data
  • Melatoninno data
  • Neurotrophinsno data
  • Blood flowno data
  • Nitric oxideno data
  • Energy metabolismmodulated · Lean mass rises, abdominal and total fat remain unchanged; basal metabolic rate higher only temporarily[5][8]
  • Insulin · glucosemodulated · Fasting blood glucose rises, insulin sensitivity falls; glucose tolerance test worsened[5][8][11]
  • Inflammation · oxidativeno data
  • Stress axis↑ · Cortisol elevated in the two-year study; only temporary in obesity[5][8]
  • Testosterone axisno data
  • Endocannabinoidsno data
  • Autophagy · senescenceno data
  • Immune systemno data
  • Lipid metabolismno data
  • Coagulation · fibrinolysisno data
  • Methylationno data

Routes of administration and bioavailability

How much of a compound reaches the blood or target tissue depends on the route into the body and on the dosage form. All routes of administration explained

  • Oral (swallowed) · Tablet or solution

    not determined; effective by mouth (all human studies)

    All studies used oral administration [5][7][8]; the GH increase was stronger after the first dose than after weeks [5].[7][8]

    Human, randomised

Human studies

  • Two years in healthy older people

    RCT, double-blind, placebo-controlled, modified crossover design · healthy (aged 60–81) · n = 65 · 2 years (primary endpoints after 1 year)

    Measured: lean mass, abdominal fat; also strength, function, metabolism

    Result: Lean mass +1.1 kg versus −0.5 kg; abdominal and total fat unchanged; weight +2.7 kg; fasting glucose higher, insulin sensitivity lower, cortisol higher; strength and function unchanged.[8]

    Human, randomised

  • Alzheimer's disease

    RCT, double-blind, multicenter · Patients: mild to moderate Alzheimer's disease · n = 563 · 12 months

    Measured: CIBIC-plus, ADAS-Cog, ADCS-ADL, CDR-sob

    Result: IGF-1 raised by 60.1% (6 weeks) and 72.9% (12 months); no difference in any endpoint.[9]

    Human, randomised

  • After hip fracture

    RCT, double-blind, placebo-controlled, phase 2b · Patients: older people after hip fracture · n = 123 · 24 weeks (stopped early)

    Measured: functional tests, IGF-1

    Result: IGF-1 +51.4 ng/ml; gait speed better, stair-climbing performance and other tests not; stopped because of cases of heart failure.[10]

    Human, randomised

  • Obesity over two months

    RCT, double-blind, placebo-controlled, parallel · healthy (men with obesity) · n = 24 · 8 weeks

    Measured: GH, IGF-1, body composition, energy expenditure

    Result: IGF-1 about +40%, lean mass higher, total and abdominal fat unchanged, basal metabolic rate higher only after 2 weeks, glucose tolerance test worsened.[5]

    Human, randomised

  • Bone metabolism

    RCT, double-blind, placebo-controlled, parallel · healthy (men with obesity) · n = 24 · 8 weeks

    Measured: markers of bone formation and resorption

    Result: Formation markers +15 to +28%, resorption markers +23 to +46%.[6]

    Human, randomised

  • Sleep quality

    placebo-controlled crossover study (young group) or open dose sequence (older group) · healthy (18–30 and 65–71 years) · n = 14 · 7 or 14 days per period

    Measured: sleep EEG

    Result: About 50% more stage IV and over 20% more REM sleep in the younger group; almost 50% more REM sleep in the older group.[7]

    Human, randomised

  • Protein breakdown under caloric restriction

    RCT, double-blind, placebo-controlled, crossover · healthy · n = 8 · 2 × 14 days

    Measured: nitrogen balance

    Result: Balance +0.31 instead of −1.48 grams of nitrogen per day.[4]

    Human, randomised

  • Combination with a SARM (case report)

    case report, self-administration · healthy (25-year-old man) · n = 1 · 5 weeks

    Measured: body composition, blood values

    Result: More body mass, but liver enzymes up to +205%, LDL +40%, HDL −36%, total testosterone −62%; mostly back to baseline after discontinuation.[12]

    Human, non-randomised

Risks and warnings

  • Insulin resistance and higher blood glucose

    In the two-year study, fasting glucose rose and insulin sensitivity fell [8]; in obesity, the glucose tolerance test worsened [5]. A review calls this the most important known disadvantage of the class of compounds [11].

    Human, randomised

  • Heart failure signal

    The study in people after hip fracture was stopped early because of cases of heart failure; the authors rate the safety profile in this group as unfavorable [10].

    Human, randomised

  • Increased appetite, fluid retention, muscle pain

    Most common side effects in the two-year study; the increased appetite subsided after a few months, yet body weight still rose by 2.7 kg [8].

    Human, randomised

  • Cortisol increase

    Cortisol was elevated over two years [8]; only temporary in obesity [5].

    Human, randomised

  • Increased bone turnover

    Formation and resorption markers rose simultaneously [6]; whether this improves or worsens bone strength is open [8].

    Human, randomised

  • Lack of long-term safety

    Data on cancer incidence and mortality with long-term use are lacking [11]; the longest study lasted two years [8].

    No data

  • Combination with SARMs

    A case report on MK-677 plus LGD-4033 describes sharply elevated liver enzymes, worsened blood lipids, and collapsed testosterone [12]; what share MK-677 has in this is unclear.

    Human, non-randomised

  • Product quality

    In an analysis of 44 products sold online as SARMs, 17 (39%) contained a different unapproved active substance, including ibutamoren; 11 (25%) contained undeclared substances, and only 18 (41%) matched the label in amount [17]. Products explicitly sold as MK-677 were not examined separately there.

    Laboratory

  • Doping

    Ibutamoren is listed by name in the 2026 WADA Prohibited List (S2.2.4, growth hormone secretagogues) [16] and in the Annex to the German Anti-Doping Act (II.2.4) [13]; a review also describes the prohibition of the class of compounds [3].

    No data

Interactions

  • LGD-4033 (SARM): In a case report, marked changes in liver enzymes, blood lipids, and testosterone occurred under the combination [12].

Fact check: common claims

  • refuted

    “MK-677 is a peptide”

    It is a small molecule that works by mouth (spiroindoline sulfonamide), not a peptide; it merely acts at the same receptor as the peptides of this group [1].

  • partly supported

    “MK-677 builds muscle and makes you stronger”

    Lean mass rose by about 1 kg, but strength and everyday function did not [8].

  • refuted

    “MK-677 burns fat”

    Abdominal and total fat remained unchanged in both studies, and limb fat even increased [5][8].

  • not supported

    “MK-677 is safer than growth hormone because the body's own regulation is preserved”

    The feedback remains intact [3], but insulin sensitivity, cortisol, and a heart failure signal argue against harmlessness [8][10][11].

  • partly supported

    “MK-677 improves sleep”

    A single small study showed more deep and REM sleep [7]; a replication is lacking.

Pharmacokinetics

Absorption
Effective by mouth [5][8].
Half-life
Not verified.
Metabolism
Not verified.
Entry into the brain
Receptors are located in the pituitary and hypothalamus [1]; no own measurements of brain penetration were found.

Legal status

Germany
Ibutamoren is listed in the Annex to the German Anti-Doping Act (AntiDopG) under II.2.4 (growth hormone releasing factors, group “growth hormone secretagogues (GHS) and their mimetics”) as “ibutamoren, synonym MK-677, Nutrabol”; the closing sentence of the Annex includes “the various salts, esters, ethers, isomers, mixtures of isomers, complexes or derivatives”, thus also salts such as the mesylate [13]. Paraphrase of the provision: under Section 2 paragraph 3 AntiDopG, it is prohibited to acquire, possess, or bring into the country doping agents containing a substance of this Annex in a not insignificant quantity for the purpose of doping in sport in humans. Section 2 paragraphs 1 and 2 prohibit, without a quantity limit, manufacturing, trading in, selling, dispensing, or otherwise placing on the market, prescribing, or administering to another person doping agents containing a substance of Annex I of the International Convention against Doping for the purpose of doping in sport in humans [13]. The version of the prohibited list published in Part II of the Federal Law Gazette is authoritative for this; the 2026 WADA list names ibutamoren under S2.2.4 [16], and the German publication was not checked. No entry in AMVV Annex 1 [14]; a national marketing authorization (AMIce/PharmNet) was not queried.
EU
No centrally authorized or assessed medicinal product containing ibutamoren in the EMA data export (as of October 24, 2026) [15]. Status under food law not verified.
USA
Not approved as a drug. The FDA lists ibutamoren mesylate for pharmacy compounding in category 2 of bulk drug substances with potential significant safety risks (under section 503A since September 29, 2023, under 503B since December 29, 2022) and justifies this with the heart failure signal of the study after hip fracture [2].
Other countries
Sport: The 2026 WADA Prohibited List (in force since January 1, 2026) names under S2.2.4 “growth hormone secretagogues (GHS) and their mimetics [e.g. anamorelin, capromorelin, ibutamoren (MK-677), ipamorelin, lenomorelin (ghrelin), macimorelin and tabimorelin]” (original English wording from the WADA PDF, retrieved October 24, 2026) [16]; likewise a review [3].

Related compounds

GHRP-6same class (German only)Hexarelinsame class (German only)Ipamorelinsame class (German only)

Open questions

  • Why does more lean mass not lead to more strength and better function?
  • Is the heart failure signal from the hip fracture study a real effect?
  • What does the reduced insulin sensitivity do over years, especially with pre-existing conditions?
  • Does the permanent IGF-1 increase raise cancer risk?

References

  1. Howard AD, Feighner SD, Cully DF, Arena JP, Liberator PA, Rosenblum CI, et al. A receptor in pituitary and hypothalamus that functions in growth hormone release. Science. 1996;273(5277):974–7. doi:10.1126/science.273.5277.974 · PubMed
  2. U.S. Food and Drug Administration. Certain bulk drug substances for use in compounding that may present significant safety risks [Internet]. Silver Spring (MD): FDA; [aktualisiert 22.04.2026; abgerufen 24.10.2026]. Verfügbar unter: https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks
  3. Dominikowski A, Rękoś Z, Olejarz M, Szczepanek-Parulska E, Domin R, Ruchała M. The emerging landscape of performance-enhancing peptides modulating GH-IGF1 axis: bridging the gap between clinical evidence and patient self-administration. Front Endocrinol (Lausanne). 2026;17:1822475. doi:10.3389/fendo.2026.1822475 · PubMed
  4. Murphy MG, Plunkett LM, Gertz BJ, He W, Wittreich J, Polvino WM, et al. MK-677, an orally active growth hormone secretagogue, reverses diet-induced catabolism. J Clin Endocrinol Metab. 1998;83(2):320–5. doi:10.1210/jcem.83.2.4551 · PubMed
  5. Svensson J, Lönn L, Jansson JO, Murphy G, Wyss D, Krupa D, et al. 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):362–9. doi:10.1210/jcem.83.2.4539 · PubMed
  6. Svensson J, Ohlsson C, Jansson JO, Murphy G, Wyss D, Krupa D, et al. Treatment with the oral growth hormone secretagogue MK-677 increases markers of bone formation and bone resorption in obese young males. J Bone Miner Res. 1998;13(7):1158–66. doi:10.1359/jbmr.1998.13.7.1158 · PubMed
  7. Copinschi G, Leproult R, Van Onderbergen A, Caufriez A, Cole KY, Schilling LM, et al. Prolonged oral treatment with MK-677, a novel growth hormone secretagogue, improves sleep quality in man. Neuroendocrinology. 1997;66(4):278–86. doi:10.1159/000127249 · PubMed
  8. Nass R, Pezzoli SS, Oliveri MC, Patrie JT, Harrell FE, Clasey JL, et al. 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):601–11. doi:10.7326/0003-4819-149-9-200811040-00003 · PubMed
  9. Sevigny JJ, Ryan JM, van Dyck CH, Peng Y, Lines CR, Nessly ML. Growth hormone secretagogue MK-677: no clinical effect on AD progression in a randomized trial. Neurology. 2008;71(21):1702–8. doi:10.1212/01.wnl.0000335163.88054.e7 · PubMed
  10. Adunsky A, Chandler J, Heyden N, Lutkiewicz J, Scott BB, Berd Y, et al. 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):183–9. doi:10.1016/j.archger.2010.10.004 · PubMed
  11. Sigalos JT, Pastuszak AW. The safety and efficacy of growth hormone secretagogues. Sex Med Rev. 2018;6(1):45–53. doi:10.1016/j.sxmr.2017.02.004 · PubMed
  12. Cardaci TD, Machek SB, Wilburn DT, Heileson JL, Harris DR, Cintineo HP, et al. LGD-4033 and MK-677 use impacts body composition, circulating biomarkers, and skeletal muscle androgenic hormone and receptor content: a case report. Exp Physiol. 2022;107(12):1467–76. doi:10.1113/EP090741 · PubMed
  13. Gesetz gegen Doping im Sport (Anti-Doping-Gesetz – AntiDopG), § 2 Absatz 1 bis 3 (https://www.gesetze-im-internet.de/antidopg/__2.html) und Anlage (zu § 2 Absatz 3), II.2.4: „Ibutamoren, synonym MK-677, Nutrabol“, mit Schlusssatz zu Salzen, Estern, Ethern, Isomeren, Komplexen und Derivaten. Fundstelle der Anlage: BGBl. 2023 I Nr. 67, 1–5. https://www.gesetze-im-internet.de/antidopg/anlage.html (abgerufen am 24.10.2026).
  14. Verordnung über die Verschreibungspflicht von Arzneimitteln (Arzneimittelverschreibungsverordnung – AMVV), Anlage 1 (zu § 1 Nr. 1 und § 5). Stand: zuletzt geändert durch Art. 1 V v. 19.5.2026 (BGBl. 2026 I Nr. 149). https://www.gesetze-im-internet.de/amvv/anlage_1.html (abgerufen am 24.10.2026; kein Eintrag „Ibutamoren“).
  15. European Medicines Agency. Medicines: Datenexport (JSON) der zentral bewerteten Arzneimittel. Amsterdam: EMA; Zeitstempel 24.10.2026. https://www.ema.europa.eu/en/documents/report/medicines-output-medicines_json-report_en.json (abgerufen am 24.10.2026; Suche nach „ibutamoren“ ohne Treffer).
  16. World Anti-Doping Agency. World Anti-Doping Code International Standard: Prohibited List 2026 (in Kraft ab 1. Januar 2026), Abschnitt S2.2.4. Montreal: WADA; 2025. https://www.wada-ama.org/sites/default/files/2025-09/2026list_en_final_clean_september_2025.pdf (englischer Originaltext, abgerufen am 24.10.2026).
  17. Van Wagoner RM, Eichner A, Bhasin S, Deuster PA, Eichner D. Chemical composition and labeling of substances marketed as selective androgen receptor modulators and sold via the internet. JAMA. 2017;318(20):2004–10. doi:10.1001/jama.2017.17069 · PubMed
How this profile was checked

Last reviewed: 2026-10-25. All sources with a DOI or PMID were resolved automatically via Crossref or doi.org and PubMed.

Translated from the German profile (version of 2026-10-25); translation checked on 2026-10-26.

Checked

  • October 25, 2026 (decision q036/E-2, Tilman): `kategorie` changed from “Supplement” to “Nicht zugelassener Wirkstoff”. Basis in the profile: no centrally authorized medicinal product in the EMA data export [15], no entry in AMVV Annex 1 [14], doping agent under the AntiDopG Annex [13] and the WADA list [16], not approved as a drug in the United States [2]. National authorizations (AMIce) and the status under food law remain unverified (research assignment docs/AUFTRAG-RECHTSSTATUS.md). Claims, levels, and results unchanged.
  • October 25, 2026 (q012): The ratings in `versprechen` and `behauptungen` are based only on the abstracts (abstract only checked); full text only for the review [3] (PMC13322892).
  • Cross-check October 24, 2026: Section 2 AntiDopG reread in the statutory text (paragraphs 1 and 2 refer to Annex I of the International Convention against Doping in the version published in Part II of the Federal Law Gazette, paragraph 3 to the Annex to the Act); closing sentence of the Annex “The enumeration includes the various salts, esters, ethers, isomers, mixtures of isomers, complexes or derivatives.” [13]; WADA list 2026, S2.2.4 with “ibutamoren (MK-677)” [16]. Penal provisions (Section 4) not reproduced.
  • Legal status checked against primary sources on October 24, 2026 (package kat-p5): AntiDopG Annex (Federal Law Gazette 2023 I No. 67) in full text, ibutamoren under II.2.4 (not II.2.3), wording “Ibutamoren, synonym MK-677, Nutrabol”, Section 2 paragraph 3 read in the statutory text [13]; AMVV Annex 1 without an entry “Ibutamoren” [14]; EMA data export without a hit [15]; WADA list 2026 loaded as a PDF via the browser (direct retrieval answered with HTTP 202), wording of S2.2.4 as cited [16]. Van Wagoner 2017 at the abstract: 44 products, 23 (52%) with a SARM, 17 (39%) with another unapproved active substance (including ibutamoren), 4 (9%) without an active substance, 11 (25%) with undeclared substances, amount as declared in only 18 (41%) [17].
  • Local check on October 24, 2026: FDA page “Certain bulk drug substances … significant safety risks” (as of April 22, 2026) read: ibutamoren mesylate in category 2 for 503A (since September 29, 2023) and 503B (since December 29, 2022), rationale heart failure signal of the hip fracture study [2]. The earlier statement according to Renke & Chinellato 2026 (“approved compounding substance”) was wrong and was replaced; the review is no longer a source. Key figures [7][8][9][10] rechecked against the abstracts; statements on timing and frequency of intake removed.
  • All abstracts read via PubMed (XML), DOIs and PMIDs reconciled with tools/pruefe_profile.py.
  • Key figures checked against abstracts: receptor cloning [1]; nitrogen balance +0.31 vs. −1.48 g/day, n = 8 [4]; n = 24, IGF-1 ≈ +40%, lean mass ↑, fat unchanged, basal metabolic rate only after 2 weeks, glucose tolerance worsened, cortisol transient [5]; bone markers +15 to +46% [6]; n = 8 + 6, stage IV ≈ +50%, REM > +20% or ≈ +50% [7]; n = 65, lean mass +1.1 vs. −0.5 kg, weight +2.7 vs. +0.8 kg, fasting glucose +0.3 mmol/l, cortisol +47 nmol/l, limb fat +1.1 vs. +0.24 kg, no change in strength or function [8]; n = 563, IGF-1 +60.1% and +72.9%, no effect [9]; n = 123, IGF-1 +51.4 ng/ml, gait speed p = 0.011, stopped because of heart failure [10]; insulin sensitivity as the main concern, missing cancer and mortality data [11]; case report: liver enzymes +205%, LDL +40%, HDL −36%, total testosterone −62% [12].
  • In the full text (PMC13322892): preserved feedback via somatostatin and IGF-1, GH secretagogues on the WADA Prohibited List [3].
  • ClinicalTrials.gov: 8 entries each for “ibutamoren” and for “MK-677” (October 23, 2026); no entry from “Hudson Biotech”.
  • Precision flags (m004, implemented by Claude October 26, 2026, pending confirmation by Tilman): “More muscle mass and less fat” → “kleine_studien”: [5] n = 24, [8] n = 65 (each per abstract).
  • Precision flags (m004, implemented by Claude October 26, 2026, pending confirmation by Tilman): “Deeper sleep” → “kleine_studien”: [7] n = 14 (8 younger, 6 older; abstract).
  • Precision flags (m004, implemented by Claude October 26, 2026, pending confirmation by Tilman): “Strengthens the bones” → “kleine_studien”: [6] n = 24, [8] n = 65 (each per abstract).
  • Precision flags (m004, implemented by Claude October 26, 2026, pending confirmation by Tilman): “Protects the brain from Alzheimer's” → “herstellerfinanziert”: [9] first author affiliated with Merck Research Laboratories according to the affiliation; Merck & Co. supplied the study drug MK-677 according to [8].
  • Cross-check October 26, 2026 (m004, implemented by Claude, pending confirmation by Tilman): evidence for the precision flags that were set (participant numbers or funding and conflict-of-interest statements) carried over from the review notes into the rationale so that readers can verify them; participant numbers rechecked against the PubMed abstracts.

Not verified

  • National marketing authorization (AMIce/PharmNet) and status under food law in Germany and the EU not checked; whether a “not insignificant quantity” has been set for ibutamoren under the German Doping Agent Quantities Ordinance not checked (page not reachable).
  • Pharmacokinetics (half-life, bioavailability): no primary source found.
  • Whether the heart failure signal in [10] was confirmed in further studies or reporting systems.
  • Composition and purity of products explicitly sold as MK-677: no own analysis found; [17] examined products sold as SARMs. The 2025 GEON market surveillance (according to the scope, PMID 40551438) was not read.
  • German publication of the 2026 WADA list in Part II of the Federal Law Gazette not checked; the English original text is cited [16].

No dosages, no sources of supply. This information does not replace medical advice.

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