MK-677 (Ibutamoren): Benefits, Dosage and Side Effects
MK-677 (ibutamoren): the non-peptide GH secretagogue explained, common research dosing, FDA-flagged and trial-reported side effects, and legal status.
The short version
MK-677, also called ibutamoren, is not a peptide. It is a small oral molecule that raises growth hormone and IGF-1 by acting on the ghrelin receptor. Trials in older adults and obese men found it increased fat-free mass. It has never been FDA-approved, and FDA cites a hip-fracture trial that was stopped early over a possible heart-failure signal.
- MK-677 is a small molecule taken by mouth, not a peptide like CJC-1295 or ipamorelin.
- Never approved by the FDA or any other regulator for any use.
- FDA flags a possible heart-failure signal from a hip-fracture trial that was stopped early.
- Banned at all times in sport under WADA section S2.
MK-677 (Ibutamoren) at a glance
- What it is
- Non-peptide, orally active growth hormone secretagogue (ghrelin receptor agonist)
- Main use
- Developed as an oral, non-injectable alternative to peptide growth hormone secretagogues. Published trials in healthy older adults and obese men found it raised growth hormone and IGF-1 and increased fat-free mass; FDA references a hip-fracture trial that was stopped early. Marketed to consumers as a research chemical for muscle and recovery, a use never approved by any regulator.
- Also called
- Ibutamoren, Ibutamoren mesylate, L-163,191, MK 677
- Molecular formula
- C27H36N4O5S (528.7 g/mol) Structure
- Evidence
- Limited human data
- US status
- Research use only
- Half-life
- Not established in humans
- How it is taken
- By mouth
- Common protocol
- 12.5-25 mg, once daily by mouth; the published 2008 trial dosed each morning, while compounding-pharmacy protocols commonly move dosing to before bed, for 8-12 weeks (common practice, not trial-established) Dosing page
MK-677 is not a peptide. Every other growth-hormone-axis compound on this site (CJC-1295, ipamorelin, sermorelin, GHRP-2, GHRP-6) is a chain of amino acids given by injection. MK-677 (ibutamoren) is a small organic molecule taken as a capsule or liquid. It is usually sold alongside those peptides as if it were one of them.
Dosing: what the human trials used.
What is MK-677?
Ibutamoren is described as an agonist at the ghrelin receptor (GHS-R1a), the same receptor that peptides such as GHRP-2 and GHRP-6 act on. Researchers report that it triggers pulses of growth hormone from the pituitary and raises IGF-1.
Its appeal is that it works by mouth: no mixing, no needle. Raising a hormone level is a mechanism, though, not a proven health benefit.
MK-677 (Ibutamoren) structure
- Molecular formula
- C27H36N4O5S
- Molecular weight
- 528.7 g/mol
- PubChem CID
- 178024
A small non-peptide molecule. It is usually sold as the mesylate salt (ibutamoren mesylate); the diagram is the free base.
Identity checked against ChEMBL (EMBL-EBI).
MK-677 benefits: what the research shows
Small or uncontrolled human studies. Too little to settle the question either way. FDA references a placebo-controlled trial in hip-fracture patients that was stopped early over a possible heart-failure signal. Three published human trials measured MK-677's effect on growth hormone and IGF-1 in healthy older adults and obese men; the dosing page has the doses and findings. None tested muscle strength, athletic performance or any outcome in the younger people most vendors market it to, so efficacy claims for that use remain unverified.
MK-677 has more controlled human data than most compounds sold alongside it. Three published trials (one dose-ranging, two later) gave 25 mg a day by mouth to healthy older adults or obese men. They found it raised growth hormone and IGF-1 and increased fat-free mass.
That is a real, repeated effect on body composition in people, which most research peptides can’t show. The doses, populations and findings are on the dosing page.
FDA also references a fourth randomised trial, in hip-fracture recovery, that was stopped early for safety reasons.
What people who use it report
MK-677 is widely sold as an oral “research chemical”, often combined with SARMs or labelled as one. The US military’s Operation Supplement Safety programme notes that FDA has sent warning letters to companies illegally selling it. Case reports describe it as increasingly used by recreationally active people Cardaci 2022 - Cardaci TD, Machek SB, Wilburn DT 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):1467-1476., in the references below and gaining popularity as a performance-enhancing supplement Cobani 2025 - Cobani E, Amin MS, Hasso M et al. Hepatotoxicity induced by MK-677. BMJ Case Rep. 2025;18(7)., in the references below.
What is documented about people taking it on their own:
- Why people take it. It is marketed to build muscle, reduce body fat and increase energy, according to Operation Supplement Safety.
- Gains, with trade-offs, in one measured case. A 25-year-old man took 15 mg of MK-677 a day with the SARM LGD-4033 for five weeks and let researchers measure him. He gained lean mass (+3.1%) and was stronger than trained non-users in earlier published data. He also gained fat (+15.4%), his LDL cholesterol rose 40%, a liver enzyme roughly tripled and total testosterone fell by about 60%. Most values returned to baseline after he stopped. With two drugs taken together, the case can’t say which did what Cardaci 2022 - Cardaci TD, Machek SB, Wilburn DT 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):1467-1476., in the references below.
- Side effects. Operation Supplement Safety lists anxiety, diarrhoea, fluid retention and swelling, increased hunger, muscle or joint pain, numbness and nausea. One case report describes a man in his early 30s whose liver enzymes rose after two months of MK-677 and returned to normal once he stopped Cobani 2025 - Cobani E, Amin MS, Hasso M et al. Hepatotoxicity induced by MK-677. BMJ Case Rep. 2025;18(7)., in the references below.
I found no published survey of MK-677 users, so none of this shows how often a benefit or problem occurs. Single cases can’t separate MK-677 from placebo, other substances or changes in training and diet. That is why the controlled trials carry more weight.
MK-677 dosage
No dose is FDA-approved. Research-community sources describe 12.5-25 mg by mouth once a day, often before bed to match the night-time growth hormone pulse, in 8-12 week cycles with a 4-week break. That is common practice, not a tested regimen.
The upper end, 25 mg, matches the published human trials. But those trials gave it each morning, continuously, with no breaks. Full sourcing: MK-677 dosage.
MK-677 side effects
The most concrete fact about MK-677’s human safety is its entry on FDA’s list of bulk drug substances that may present significant safety risks. Three other published trials, in older adults and obese men, add the effects listed below.
Rare but serious
That trial, in people recovering from hip fracture, stopped early because of a heart safety signal, not because it reached its planned end.
Reported in studies
The three other trials report a consistent pattern:
- increased appetite
- temporary lower-leg swelling and muscle pain
- higher fasting glucose with reduced insulin sensitivity
- a small rise in cortisol
- lower total testosterone in men
Full findings and doses: MK-677 side effects.
Get emergency care for shortness of breath, rapid or unexplained swelling, chest pain, or signs of a severe allergic reaction. MK-677 is swallowed, not injected, so injection-site reactions don’t apply.
Is MK-677 legal?
US legal status - Research use only
Sold for laboratory research use only. Not approved by the FDA for human use, and cannot be lawfully marketed as a supplement or a medicine. Products sold this way are not made to pharmaceutical quality standards, and their contents are not verified by anyone.
- Not FDA-approved for any use. DailyMed’s only ibutamoren mesylate listing is a bulk powder for animal drug compounding, not a human drug.
- FDA placed ibutamoren mesylate in category 2 of its interim bulk drug substance compounding policies, under both 503A (added 29 September 2023) and 503B (added 29 December 2022). That category is for nominated substances with potential significant safety risks.
- It is sold as an oral research chemical outside the approved supply chain. No regulator checks that a product matches its label.
- WADA’s current Prohibited List names it under S2 (Peptide Hormones, Growth Factors, Related Substances and Mimetics), banned at all times. I confirmed this by searching “ibutamoren” on wada-ama.org on 24 September 2026.
Related reading
- Does MK-677 cause hair loss?
- MK-677 cycle length
- CJC-1295 - an injectable peptide GHRH analogue, for comparison
- Ipamorelin - an injectable peptide growth hormone secretagogue
- Oral peptides - which peptides and lookalikes work by mouth, MK-677 among them
- Research peptides and the law
- Are peptides safe?
Side effects in detail, including hair loss: MK-677 side effects. Compared with an approved GH-axis drug: Tesamorelin vs MK-677.
Regulatory changes for this compound and others, as they happen: US peptide regulation tracker.
How MK-677 (Ibutamoren) compares
Secretagogues (act on the ghrelin receptor). Doses for unapproved compounds are common practice, not trial-established. All growth hormone and muscle peptides →
| Compound | Main use | Evidence | Usual dose | US status |
|---|---|---|---|---|
| Ipamorelin | Investigated for postoperative ileus, reaching Phase 2 before being discontinued for insufficient efficacy. Marketed to consumers for growth hormone release, an application never approved anywhere. | Limited human data | 100-300 mcg, once nightly on 5 days a week in physician-supervised protocols, up to three times daily on an empty stomach in less structured use | Research use only |
| MK-677 (Ibutamoren) | Developed as an oral, non-injectable alternative to peptide growth hormone secretagogues. Published trials in healthy older adults and obese men found it raised growth hormone and IGF-1 and increased fat-free mass; FDA references a hip-fracture trial that was stopped early. Marketed to consumers as a research chemical for muscle and recovery, a use never approved by any regulator. | Limited human data | 12.5-25 mg, once daily by mouth; the published 2008 trial dosed each morning, while compounding-pharmacy protocols commonly move dosing to before bed | Research use only |
| GHRP-2 | Sold to consumers as a growth-hormone-release research chemical for muscle and recovery use, an application never approved anywhere. Historically investigated as a pituitary growth-hormone stimulus and diagnostic agent. | Limited human data | 100-300 mcg, 2 to 3 times daily, on an empty stomach, 5 days a week (5 on, 2 off) | Research use only |
| GHRP-6 | One of the original growth hormone-releasing peptides, studied since the 1980s as a pituitary GH secretagogue. Marketed to consumers for muscle and recovery goals, an application never approved anywhere. | Limited human data | 100-300 mcg, 2 to 3 times daily, on an empty stomach, spaced at least 3-4 hours apart | Research use only |
| Hexarelin | Investigated since the 1990s as a growth hormone-releasing peptide (GHRP), including for growth-hormone stimulation testing. Sold to consumers as a research chemical for muscle and recovery use, an application with no controlled human trial behind it. | Limited human data | 80-160 mcg, once or twice daily (morning and/or before bed), on an empty stomach | Research use only |
Where to buy MK-677 (Ibutamoren) for research
Each vendor is checked against my vendor checklist.
I don't list a vendor for MK-677 (Ibutamoren) yet. Before buying from anyone, work through the vendor checklist.
Common questions
Is MK-677 a peptide?
No. MK-677 (ibutamoren) is a small organic molecule that works when swallowed. It is grouped with peptide growth hormone secretagogues such as CJC-1295 and ipamorelin because it acts on a related pathway, the ghrelin receptor. Chemically it is a different class of compound.
Is MK-677 FDA-approved?
No. FDA has never approved it for anything. DailyMed's only ibutamoren mesylate listing is a bulk powder for animal drug compounding, not a human drug. FDA has placed it in category 2 of its bulk-substance compounding policies over a potential safety risk.
Is MK-677 safe?
FDA says ibutamoren mesylate poses significant safety risks because of possible congestive heart failure in certain patients. It cites a placebo-controlled trial in people recovering from hip fracture that was stopped early over a possible heart-failure signal. There is no long-term human safety data.
Is MK-677 banned in sport?
Yes. The current WADA Prohibited List bans it at all times under section S2, which covers peptide hormones, growth factors, related substances and mimetics.
Is MK-677 a steroid?
No. Ibutamoren is a small-molecule ghrelin-receptor agonist, not a steroid hormone. WADA's Prohibited List keeps them apart: anabolic steroids are under S1 (Anabolic Agents), and ibutamoren is under S2 (Peptide Hormones, Growth Factors, Related Substances and Mimetics).
Does MK-677 affect muscle growth?
No human trial I can verify shows it builds muscle. Three published trials in older adults or obese men on 25 mg a day found fat-free mass increased, but none measured strength or performance, and none enrolled younger adults who train. The hip-fracture trial FDA cites was stopped early over a heart signal and didn't measure muscle either.
Is MK-677 hard on the kidneys?
No kidney-specific risk appears in the sources this page cites. FDA's safety listing for ibutamoren mesylate flags only a heart signal and doesn't mention the kidneys. No flag isn't proof of safety: there is no long-term human safety data for MK-677.
Does MK-677 hurt your liver?
FDA's safety listing flags only a heart signal and doesn't mention the liver. One case report describes a man in his early 30s whose liver enzymes rose after two months of MK-677 and returned to normal after he stopped. A single case can't show how common that is, and no long-term human data confirm or rule out a liver risk.
How long does MK-677 take to work?
No source I can verify says, for muscle or training. Trials measured hormone changes over 2-4 weeks and fat-free mass over 8 weeks to 2 years, in older or obese people, not people who train. Treat any specific timeframe for muscle or performance as unverified.
What is the usual MK-677 dose?
No dose is FDA-approved. Research-community sources describe 12.5-25 mg by mouth once a day, often before bed, in 8-12 week cycles with a 4-week break. That is common practice, not a tested regimen. The published trials used 25 mg, but each morning and continuously. See the dosing page for the sourcing.
What are the side effects of MK-677?
FDA's safety flag is a possible heart-failure signal from a hip-fracture trial stopped early. Three other published trials report increased appetite, temporary fluid retention and muscle pain, higher fasting glucose with lower insulin sensitivity, a small cortisol rise, and lower testosterone in men. Full detail is on the MK-677 side effects page.
References (7 sources)
Bibliographic detail is fetched from PubMed, not written by me - so a citation here cannot drift from the paper it names. Study design comes from PubMed's own tags rather than my judgement.
- 1.Cardaci TD, Machek SB, Wilburn DT 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):1467-1476.Case reportPMID 36303408
- 2.Copinschi G, Leproult R, Van Onderbergen A et al. Prolonged oral treatment with MK-677, a novel growth hormone secretagogue, improves sleep quality in man. Neuroendocrinology. 1997;66(4):278-86.Clinical trialPMID 9349662
- 3.Cobani E, Amin MS, Hasso M et al. Hepatotoxicity induced by MK-677. BMJ Case Rep. 2025;18(7).Case reportPMID 40675653
- 4.FDA - Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks. Ibutamoren mesylate entry: category 2 under 503A and 503B, congestive heart failure risk, hip-fracture RCT terminated early.- US Food and Drug Administrationregulatory
- 5.DailyMed - AX Pharmaceutical Corp, ibutamoren mesylate powder. Listed as a bulk ingredient for animal drug compounding, not an FDA-approved human drug product.- DailyMed, US National Library of Medicinelabel
- 6.WADA Prohibited List search tool - searching "ibutamoren" returns one result, classified under S2 (Peptide Hormones, Growth Factors, Related Substances and Mimetics), prohibited at all times. Verified by keyword search on 2026-09-24.- World Anti-Doping Agencyregulatory
- 7.Operation Supplement Safety (US Department of Defense), 23 February 2024 - Performance-enhancing substance: MK-677 (ibutamoren). Notes FDA warning letters to companies illegally selling it, that it is marketed to build muscle, reduce body fat and increase energy and often combined with or sold as a SARM, and lists reported side effects.- Operation Supplement Safety, US Department of Defenseregulatory