Research
What Is MK-677 (Ibutamoren)? The Oral GH Secretagogue
MK-677, also called ibutamoren, is one of the few compounds that can raise growth hormone when taken by mouth. It was developed by Merck in the 1990s and tested in several clinical trials before development stopped. It is often grouped with SARMs and peptides, but it is neither. This guide explains what MK-677 is, what the human trials showed, and the side effects that kept it from approval.
Reviewed for accuracy · Last reviewed October 19, 2026
What Is MK-677?
MK-677 (ibutamoren mesylate) is a small, non-peptide molecule that activates the ghrelin receptor, the same receptor targeted by ipamorelin and other growth hormone secretagogues. Merck developed it as an oral alternative to injectable growth hormone.
It is sometimes called a SARM, but it is not one. SARMs act on androgen receptors; MK-677 acts on the ghrelin receptor and does not affect testosterone directly.
How Does MK-677 Work?
- Mimics ghrelin: it activates the ghrelin receptor in the pituitary and hypothalamus, triggering growth hormone release.
- Long-acting: one oral dose works for about a day, so it keeps GH and IGF-1 raised continuously instead of in short pulses.
- Increases appetite: because ghrelin is the hunger hormone, MK-677 strongly increases appetite in many people.
What Does the Research Show?
Healthy older adults. The best-known study (Nass et al., Annals of Internal Medicine, 2008) gave MK-677 or placebo to 65 healthy adults aged 60 to 81 for one year. MK-677 raised GH and IGF-1 to levels typical of young adults and increased fat-free mass by about 1.1 kg. However, it did not improve strength or physical function, and it increased fasting blood sugar and lowered insulin sensitivity.
Hip fracture recovery. A trial in older adults recovering from hip fracture was stopped early after more cases of heart failure were seen in the MK-677 group than with placebo.
Other studies. MK-677 has also been studied for sleep quality, bone turnover and muscle wasting, with modest or mixed results. Merck did not bring it to market.
| Area | What studies show | Evidence type |
|---|---|---|
| GH and IGF-1 | Raised to young-adult levels | Human RCT (1 year) |
| Lean mass | About +1.1 kg fat-free mass | Human RCT |
| Strength and function | No improvement | Human RCT |
| Blood sugar | Higher fasting glucose, lower insulin sensitivity | Human RCT |
MK-677 Side Effects
MK-677 has more human side-effect data than most compounds sold alongside it. Reported effects include:
- Increased appetite, often strong
- Higher blood sugar and insulin resistance, a concern for people at risk of diabetes
- Water retention and swelling in the legs and feet
- Joint and muscle pain, and numbness or tingling in the hands
- Heart failure signal in frail older adults, from the stopped hip-fracture trial
Because MK-677 keeps IGF-1 elevated around the clock, researchers have also raised theoretical long-term concerns about cancer risk, which have not been studied.
Is MK-677 FDA-Approved?
No. MK-677 is not an FDA-approved drug and is not a legal dietary supplement ingredient. Unlike many peptides that the FDA moved off its restricted list in April 2026, ibutamoren remains in the FDA’s Category 2 table of compounding ingredients that may present significant safety risks.
It is also prohibited at all times by WADA as a growth hormone secretagogue.
MK-677 vs Ipamorelin and Other GH Options
| Option | How it is taken | GH pattern | Status |
|---|---|---|---|
| MK-677 (ibutamoren) | Oral | Constant elevation | Not approved; FDA Category 2 |
| Ipamorelin | Injection | Short pulse | Not approved |
| Sermorelin | Injection | Short pulse | Formerly approved; compounded |
| Tesamorelin | Injection | Short pulse | FDA-approved (Egrifta) |
| Growth hormone | Injection | Direct replacement | FDA-approved for GH deficiency |
MK-677 vs ipamorelin. Both act on the ghrelin receptor. Ipamorelin produces short GH pulses with little effect on appetite or cortisol, while MK-677 keeps GH raised all day and strongly increases appetite. The constant elevation is also what drives its blood sugar effects.
Why the oral route matters. Being a pill is MK-677’s main appeal, but the same long action that makes it convenient is linked to its most important side effects.
Buying Research-Grade MK-677: What to Check
Products sold as MK-677 by research suppliers are laboratory chemicals, not medicines. They are not made under drug manufacturing rules, so quality varies a lot between vendors. If you are evaluating an MK-677 supplier for lab research, these are the checks that matter:
- Batch-specific COA: the certificate should match the lot number on your vial, not a generic sample.
- Independent lab: testing should come from a named third-party lab, ideally with a way to verify the report online.
- Identity, not just purity: HPLC purity alone does not confirm the right molecule; look for mass spectrometry (MS) identity confirmation.
- Endotoxin and sterility results: these matter for any injectable research material.
- Correct fill amount: the measured content should be close to the labeled milligrams.
Our Trusted Sources page lists vendors we track, with current community codes. Our guide to reading a certificate of analysis explains each line of a COA.
Key Takeaways
- MK-677 (ibutamoren) is an oral, non-peptide ghrelin-receptor agonist developed by Merck.
- In a one-year trial, it raised GH, IGF-1 and lean mass but did not improve strength.
- It increased blood sugar and insulin resistance, and a hip-fracture trial was stopped over heart failure cases.
- It is not FDA-approved and remains in the FDA’s Category 2 safety-risk table.
- It is banned in sport.
Frequently Asked Questions
What is MK-677?
MK-677 (ibutamoren) is an oral, non-peptide compound that activates the ghrelin receptor to raise growth hormone and IGF-1.
Is MK-677 a SARM?
No. SARMs act on androgen receptors. MK-677 acts on the ghrelin receptor and does not directly affect testosterone.
Does MK-677 build muscle?
In a one-year trial in older adults, it increased fat-free mass by about 1.1 kg but did not improve strength or physical function.
What are the side effects of MK-677?
Increased appetite, higher blood sugar and insulin resistance, water retention, joint pain and tingling. A trial in frail older adults was stopped over heart failure cases.
Is MK-677 FDA-approved?
No. It is not approved, is not a legal supplement ingredient, and remains in the FDA’s Category 2 table of compounding ingredients that may present significant safety risks.
Sources
- Annals of Internal Medicine – Nass et al. (2008), Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults
- Adunsky et al. (2011) – MK-0677 (ibutamoren mesylate) for the treatment of patients recovering from hip fracture
- FDA – Certain bulk drug substances for use in compounding that may present significant safety risks (updated April 22, 2026)
- World Anti-Doping Agency – Prohibited List, S2 peptide hormones, growth factors and related substances
MLCR SCTY provides educational information, not medical or legal advice. Research-use-only products are not intended for human consumption.