MK-677 (Ibutamoren)

What is MK-677 (ibutamoren)?

MK-677, code name MK-0677 and international name ibutamoren, is an orally active, non-peptide growth hormone secretagogue. In a 1998 human study, it was described as “an orally active, non-peptide mimetic of a growth hormone-releasing peptide.” ^[3] Ghrelin is a hormone produced in the stomach that stimulates both growth hormone release and appetite; because MK-677 stimulates this hormone’s receptor, it is also referred to as a “ghrelin mimetic.” ^[1]

MK-677 was tested in areas such as age-related muscle loss, protein breakdown during calorie restriction and Alzheimer’s disease; these trials were conducted by the research laboratories of a pharmaceutical company, or the study drug was supplied by these laboratories. ^{[1] [3] [5]} A multicenter phase 2b trial was also conducted in recovery after hip fracture. ^[4] These trials did not result in a drug approval: the FDA writes that ibutamoren is an unapproved active ingredient and that its safety and efficacy have not been proven. ^[8]

Its name often appears together with SARMs (selective androgen receptor modulators) on the internet. MK-677 is not a SARM: it acts on the ghrelin receptor, not the androgen receptor. This association comes from marketing; ibutamoren has also been found in analyses of products sold under the SARM name. ^[9] Peptides that stimulate the same receptor by injection are covered in a separate guide: GHRP-2 / GHRP-6 / Hexarelin

What did the two-year trial in older adults show?

The most detailed human data on MK-677 come from the trial published in the Annals of Internal Medicine in 2008. At a US university hospital, 65 healthy adults aged 60–81 (men, and women with and without hormone therapy) were enrolled in a 2-year, double-blind, placebo-controlled trial with a modified crossover design. The primary outcomes were lean body mass and visceral (intra-abdominal) fat at year 1. Diabetes, a body mass index of 35 or above, a history of cancer and untreated hypertension were among the exclusion criteria. ^[1]

Daily MK-677 raised GH and IGF-1 levels to the range of healthy young adults. The increase in lean mass did not lead to a change in strength or function; the authors note as a limitation that the study was not sufficient in duration and number of participants to assess functional outcomes. The 2-year exploratory analyses confirmed the year 1 results. ^[1]

The most common side effects were increased appetite that resolved within a few months (67% in the MK-677 group, 36% with placebo), transient mild leg edema (44% and 27%) and muscle pain (33% and 9%); the differences in edema and muscle pain were not statistically significant. Cortisol rose by a mean of 47 nmol/L; LDL cholesterol fell slightly from baseline. In year 1, tongue adenocarcinoma was seen in an 82-year-old woman receiving MK-677, and a heart attack 7 days after starting the drug in a 68-year-old woman; a man receiving placebo was also diagnosed with kidney cancer. All three were removed from the study. These isolated events alone do not show causality. ^[1]

The trial was an investigator-initiated study funded by the US National Institutes of Health (NIH); the study drug and placebo tablets were supplied by the research laboratories of a pharmaceutical company, and two of the authors worked in these laboratories. ^[1]

What did other human studies find?

In obesity and calorie restriction

In an 8-week randomized, double-blind trial in 24 obese men aged 18–50, IGF-1 rose by about 40% and lean mass increased significantly; total fat and visceral fat did not change significantly. Basal metabolic rate rose at week 2; the increase at week 8 was not significant. Cortisol was not higher than placebo at weeks 2 and 8. ^[2]

In a crossover trial in which 8 healthy volunteers aged 24–39 were put on calorie restriction twice for 14 days, daily nitrogen balance in the second week of restriction was a mean of +0.31 g during the period on MK-677 and −1.48 g during the placebo period; that is, short-term protein breakdown decreased. The first author of the study worked at the research laboratories of the same pharmaceutical company; the result covers only 7 days of use. ^[3]

Why was the hip fracture trial stopped early?

In the multicenter phase 2b trial in which 123 older patients with hip fracture were randomized, 62 to MK-677 and 61 to placebo, the primary outcomes were physical performance measures and IGF-1 level. At week 24, IGF-1 rose by 51.4 ng/mL versus placebo. The difference in stair-climbing power was not significant; a significant difference of 0.7 points was seen in the gait speed score; there was no improvement in other functional measures. The trial was terminated early because of a congestive heart failure safety signal seen in a limited number of patients. The authors concluded that the IGF-1 increase did not translate into improvement in most functional measures and that MK-677 carries an unfavorable safety profile in this patient group. ^[4]

The FDA keeps ibutamoren mesylate on its list of substances for compounded drug bulk ingredients that “may present significant safety risks.” As its rationale, the agency cites the possibility of congestive heart failure in some patients and reports that a randomized, placebo-controlled trial in patients recovering from hip fracture “was terminated early because of a possible congestive heart failure safety signal.” ^[6]

Alzheimer’s disease

In animal studies, IGF-1 increasing amyloid-beta clearance from the brain led to MK-677 being tested in Alzheimer’s disease. In the multicenter trial in which 563 people with mild-to-moderate Alzheimer’s disease were randomized to MK-677 or placebo for 12 months, IGF-1 rose by 60.1% at week 6 and 72.9% at month 12. Nevertheless, there was no significant difference from placebo on four clinical scales (clinician’s global impression, cognitive subscale, activities of daily living and dementia staging); 416 patients completed 12 months. The authors concluded that, although the target was reached, the drug was ineffective in slowing disease progression. The first author of the study worked at the research laboratories of a pharmaceutical company. ^[5]

Blood sugar and insulin resistance

The most consistent metabolic finding with MK-677 is on blood sugar. In the trial in older adults, fasting blood sugar did not change in the placebo group while it rose by a mean of 0.3 mmol/L (5 mg/dL) in the MK-677 group. In 16 people receiving MK-677 and 2 receiving placebo, fasting sugar rose from the normal range into the 101–110 mg/dL range; in 6 people receiving MK-677, it rose into the 110–126 mg/dL range. HbA1c rose by a mean of 0.2 points in the MK-677 group and was above 6% in 8 participants at month 12. Insulin sensitivity (QUICKI index) fell at 12 months. In four participants, the dose was reduced in a blinded manner; in two of them the reason was a fasting sugar increase. ^[1]

In obese men, fasting glucose and insulin did not change; however, the sugar-loading test showed worsening glucose balance at weeks 2 and 8. ^[2] In its warning letter, the FDA lists changes in glucose metabolism and insulin sensitivity among the possible serious side effects of ibutamoren. ^[8] Because people with diabetes were not enrolled in the trial in older adults, the size of the effect in someone with diabetes is unknown. ^[1]

What are the risks?

• Heart failure: The hip fracture trial was stopped early because of this signal; the FDA cites this risk as the rationale for the category 2 decision. ^{[4] [6]}
• Blood sugar: Increase in fasting sugar and HbA1c, reduced insulin sensitivity. ^[1]
• Appetite, fluid retention, muscle pain: These were the most commonly reported side effects in the trial in older adults. ^[1] The FDA adds fatigue to these and writes that long-term effects are unknown and that ibutamoren may interact harmfully with other medications being taken. ^[8]
• Cortisol and prolactin: Cortisol rose by a mean of 47 nmol/L in older adults. ^[1] In obese men, prolactin rose after the first dose; the increase in the area under the curve of prolactin persisted at weeks 2 and 8, while the increase in peak value did not. ^[2]
• Product content: In products sold through unsupervised channels, labels and contents often do not match (section below).

The general framework of side effects reported for peptides and similar substances is in a separate guide: Peptide side effects

What was found in products sold as supplements or under the SARM name?

Because MK-677 is sold as capsules or liquid, it is often marketed with a “supplement” or “research chemical” label. Independent analyses and official inspections show serious problems in these products:

• US, 2016: Of 44 products bought online under the SARM name, only 23 (52%) contained a SARM; 17 products (39%) contained other unapproved drugs, including ibutamoren. In 25% of products there were substances not listed on the label, and in only 41% did the amount of active substance match the label. ^[9]
• Europe and other countries, 5 years: In a market surveillance study conducted by the European network of Official Medicines Control Laboratories with 14 laboratories from 13 countries, 324 samples were examined; among the molecules within the scope of the study, the most frequently reported was ibutamoren. Of the seized products, 65% were presented as drugs and 24% as dietary supplements; the authors note that the latter situation is worrying because the user is unaware of taking an unapproved drug. ^[10]
• US, December 2025: In a warning letter sent for two products marketed as dietary supplements with claims that they support height growth in children and are “hormone-free,” the FDA reported that laboratory analysis detected ibutamoren mesylate not declared on the label in the products. ^[8]

FDA, WADA and Türkiye: what is the legal status?

United States (FDA)

According to the FDA, ibutamoren is legally outside the dietary supplement definition. The rationale is that the substance was allowed to be investigated as a new drug before being marketed as a supplement or food, and that extensive clinical investigations were publicly announced; therefore, products containing ibutamoren sold as supplements are considered unapproved new drugs. ^[8] In the FDA’s supplement ingredients directory, ibutamoren (MK-677, MK-0677, L-163,191) appears on this basis in the category “ingredients excluded from the supplement definition” and links to two warning letters dated December 2025. ^[7]

In addition, ibutamoren mesylate is in the category 2 table for compounded drug bulk ingredients (since September 29, 2023 for 503A and December 29, 2022 for 503B). ^[6] This list is not a drug approval.

Sport (WADA)

In WADA’s list effective January 1, 2026, ibutamoren (MK-677) is named among growth hormone secretagogues and mimetics under S2.2.4 “growth hormone-releasing factors.” Substances in section S2 are prohibited at all times, in and out of competition. ^[11] That undeclared ibutamoren can be found in products labeled as supplements creates an additional risk for athletes. ^[10]

Türkiye

TİTCK (Turkish Medicines and Medical Devices Agency) lists no product containing ibutamoren in its Licensed Human Medicinal Products List dated October 16, 2026. ^[12] The Ministry of Agriculture and Forestry’s Restricted Substances List for Food Supplements dated September 21, 2026 has no line for ibutamoren. ^[14]

Article 19 of Law No. 1262 on Pharmaceutical and Medicinal Preparations (İspençiyari ve Tıbbi Müstahzarlar Kanunu) punishes with imprisonment from one to five years those who manufacture unlicensed preparations and those who knowingly sell, offer for sale or have others sell preparations manufactured in this way. The same article provides the same penalty for those who sell, market or advertise a product that is not a preparation with the claim that it diagnoses or treats diseases; importing preparations made abroad without a license for commercial purposes counts as smuggling. ^[13]

The general framework in Türkiye and the national anti-doping organization are covered in a separate guide: Are peptides legal?

Evidence table: claim, population and limits

Limits of this guide

This page summarizes published human data on MK-677 (ibutamoren) and the decisions of official bodies. It gives no dose, cycle or product sourcing information; the administrations in the studies are only the description of that study. Muscle loss, recovery after fracture, blood sugar or growth problems are conditions requiring physician evaluation; suspected short stature in children requires assessment by a pediatric endocrinology specialist.