MK-677 Safety Questions: What Studies Report

MK-677 (also written MK-0677, ibutamoren) is an orally active growth hormone secretagogue that has been studied in humans, rodents and horses. A large share of public interest concerns safety: whether it affects fertility, the liver, blood sugar or hormone levels. This page summarises only what the verified published papers listed in the References section actually reported, organised by study, model, dose and duration. This page is for educational purposes only and is not medical advice; consult a licensed physician about any health question or any compound.

What the Verified Literature Covers

The body of published work on MK-677 that this page draws on is small and heterogeneous. It includes one randomised controlled trial in older adults with Alzheimer's disease, two single-subject case reports, one rodent growth study and one analytical detection study in horses. No two of these share the same population, endpoint or duration, so they cannot be pooled.

Fertility and Reproductive Outcomes: What Studies Report

This is the most searched safety question about MK-677, and the plainest answer available from the verified literature is that no study in this set measured fertility. None of the five papers reported sperm concentration, motility or morphology, time to conception, testicular volume, or any pregnancy or offspring outcome in humans.

The randomised trial in Alzheimer's disease enrolled older adults and was designed around cognitive and functional progression endpoints, not reproductive ones; researchers reported that the study found no clinical effect on Alzheimer's disease progression, and fertility was outside its scope entirely (PMID 19015485). The 2025 hepatotoxicity case report described liver injury and did not report reproductive endpoints (PMID 40675653).

The closest the literature comes to hormone-related measurement in a person using MK-677 is a case report in which one individual used LGD-4033 (a selective androgen receptor modulator) together with MK-677; researchers reported changes in body composition, circulating biomarkers, and skeletal muscle androgenic hormone and receptor content (PMID 36303408). Because two compounds were used simultaneously in a single person, the study cannot attribute any hormonal observation to MK-677 by itself, and it did not report semen analysis or fertility outcomes.

Why the absence of data is not the same as an absence of risk

Statements circulating online that MK-677 "does" or "does not" cause infertility are not supported by the papers above in either direction. An endpoint that was never measured cannot be described as safe or unsafe on the basis of those studies. The honest summary of this evidence set is: unmeasured, unknown, and not addressed by any human trial listed here.

Liver Findings: What Studies Report

A 2025 case report published in BMJ Case Reports described hepatotoxicity induced by MK-677 in a single patient (PMID 40675653). A case report documents one individual's clinical course as assessed by the treating clinicians; it establishes that such a presentation has been described and published, but a single case cannot quantify how often liver injury occurs, at what exposure, or in whom.

No controlled trial in this verified set was designed to test hepatic endpoints as its primary outcome. The 12-month randomised trial in Alzheimer's disease reported on disease progression and on tolerability during treatment, and researchers reported that it did not demonstrate a clinical benefit on progression (PMID 19015485). Readers comparing a case report against a randomised trial should note that the two answer different questions: one describes what happened to one person, the other describes average differences between groups.

Hormonal and Metabolic Measures in a 12-Month Trial: What Studies Report

The largest human dataset in this set is the randomised, placebo-controlled trial of MK-677 in patients with mild-to-moderate Alzheimer's disease, published in Neurology in 2008. Participants received 25 mg of MK-677 daily or placebo for 12 months, and the study reported that the compound raised serum insulin-like growth factor 1 (IGF-1) while producing no clinical effect on the progression of Alzheimer's disease (PMID 19015485). Researchers reported that the trial also tracked safety and tolerability measures over the treatment year, including metabolic parameters such as fasting blood glucose.

Two points follow directly from the published design. First, the population was older adults with a neurodegenerative diagnosis — not healthy younger adults, athletes, or people of reproductive age — so the reported tolerability profile describes that population under that dose and duration. Second, the trial's negative primary result concerned cognition and function; it does not speak to any other claimed use.

Combined Use With Other Compounds: What Studies Report

The 2022 case report in Experimental Physiology followed one individual using LGD-4033 and MK-677 together, and researchers reported impacts on body composition, circulating biomarkers, and skeletal muscle androgenic hormone and receptor content (PMID 36303408). The report's structure — a single participant, two compounds, no control — means that attribution of any individual finding to either compound is not possible from the data as published.

This matters for safety interpretation because much online discussion of MK-677 describes experiences in which several substances were used at once. Published case reports of that pattern, including this one, document what was observed rather than what caused it.

Animal Data on Growth: What Studies Report

A 2018 study in Yonsei Medical Journal examined the effect of orally active MK-677 on somatic growth in rats (PMID 30450851). Growth secretagogue research in rodents is typically conducted to characterise the growth hormone/IGF-1 axis under controlled conditions, and the study reported outcomes relating to somatic growth after oral administration in that animal model.

Rodent findings do not translate directly to humans. Species differ in growth hormone pulsatility, growth-plate biology and metabolism, and rodent dosing is normalised to body weight rather than to any human exposure. The rat study did not report human fertility, liver or cardiovascular outcomes.

Detection and Anti-Doping Context: What Studies Report

A 2023 paper in Drug Testing and Analysis reported the detection of MK-0677 in equine hair following oral administration (PMID 36354265). The study's purpose was analytical: to establish whether and how the compound can be identified in a hair matrix for doping-control purposes in horses.

This is not a safety study and did not report adverse events, but it is relevant context for two reasons. It confirms that MK-677 is treated as a controllable substance within regulated sport testing frameworks, and it demonstrates that residues can be recovered from hair long after administration in that species.

Populations and Endpoints With No Published Human Data

Based strictly on the verified papers summarised here, the following were not examined in any human study listed:

• Fertility and reproduction — no semen analysis, hormone-axis fertility assessment, conception or pregnancy outcome was reported in any of the five papers.
• Pregnancy and lactation — no human data were reported.
• Children and adolescents — the randomised trial enrolled adults with Alzheimer's disease (PMID 19015485); growth endpoints in this set were reported only in rats (PMID 30450851).
• Long-term use beyond 12 months — the longest human exposure reported here was the 12-month treatment period of the Alzheimer's trial (PMID 19015485).
• Cancer risk, cardiovascular events or kidney endpoints as primary outcomes — not reported as designed endpoints in any paper in this set.

Regulatory Status

MK-677 is not an approved medicine in the United States; it has been studied as an investigational growth hormone secretagogue and is commonly labelled for research use only. It is not a dietary supplement ingredient, and its presence in sport is monitored through anti-doping analysis, which is the context of the equine hair detection work (PMID 36354265).

How to Read This Evidence

1. Match the claim to the model. Effects reported in rats (PMID 30450851) are rodent findings, not human findings.
2. Weigh design. One randomised placebo-controlled trial (PMID 19015485) carries different information than a single case report (PMID 40675653).
3. Check for co-exposure. Where two compounds were used together, attribution is not possible (PMID 36303408).
4. Distinguish "no effect found" from "not studied." The Alzheimer's trial found no effect on disease progression; fertility, by contrast, was simply never measured.

Questions about personal risk, existing conditions, medications or reproductive plans belong with a licensed physician who can review an individual's history. This page reports literature only.

References

• Hepatotoxicity induced by MK-677 (BMJ Case Reports, 2025)
• LGD-4033 and MK-677 use impacts body composition, circulating biomarkers, and skeletal muscle androgenic hormone and receptor content: A case report (Experimental Physiology, 2022)
• Effect of the Orally Active Growth Hormone Secretagogue MK-677 on Somatic Growth in Rats (Yonsei Medical Journal, 2018)
• Detection of the growth hormone secretagogue MK-0677 in equine hair following oral administration (Drug Testing and Analysis, 2023)
• Growth hormone secretagogue MK-677: no clinical effect on AD progression in a randomized trial (Neurology, 2008)