Bones & muscles Non-peptide ghrelin mimetic
MK-677 (ibutamoren)
Regulatory status
Status at a glance
503A compounding status
Category 2 (significant safety risks)
FDA has identified this substance as raising significant safety risks. FDA’s interim policy does not cover it, so 503A pharmacies generally may not compound with it.
- Also known as
- Ibutamoren
- FDA approval
- Not FDA-approved for any use
- 503B outsourcing
- Not determined
- Anti-doping (WADA)
- On the WADA Prohibited List
- DEA schedule
- Not a controlled substance
About peptide status
Most peptides discussed here are not FDA-approved for any use, and products labeled “research use only” are not for human use. Removal from Category 2 does not authorize compounding. PCAC votes are non-binding recommendations; FDA and HHS make the final decisions.
This is not medical or legal advice, and we do not publish dosing, sourcing or reconstitution information. Talk with a licensed clinician before using any peptide.
If you think you are having a medical emergency, call 911.
Key takeaway
MK-677 (ibutamoren) is an orally active, non-peptide drug that mimics the hunger hormone ghrelin to raise the body's own growth hormone, sold on the wellness market for muscle, sleep, and appetite. In a randomized trial of 65 healthy adults aged 60 to 81 (Nass 2008), fat-free mass rose 1.1 kg on MK-677 versus a 0.5 kg loss on placebo over 12 months (P < 0.001), yet strength and function did not improve and fasting glucose rose. A large Alzheimer's trial failed. As of 2026 it is not FDA-approved and is banned in sport.
At a glance
- FDA status
- Non-FDA-approved, investigational drug; a small molecule, not a peptide
- What it is
- Orally active ghrelin-mimic growth hormone secretagogue
- Research
- Human trials show it raises growth hormone, IGF-1, and lean mass, but not strength or function, with metabolic signals
- Sport
- Prohibited by WADA at all times
- Evidence strength
- Moderate research
Summary
MK-677 is an oral ghrelin mimic that raises growth hormone. See what human trials show, the metabolic concerns, and why it is not FDA-approved.
What is MK-677?
MK-677, also called ibutamoren, is an orally active compound that mimics ghrelin to stimulate the body's own growth hormone. Despite being grouped with "peptides" in wellness marketing, it is a non-peptide small molecule. It was investigated by a pharmaceutical company but never approved, and it is sold through gray-market and "research chemical" channels for muscle, sleep, and appetite. It is not an approved medicine or a legitimate dietary supplement.
How does it work?
MK-677 activates the growth hormone secretagogue (ghrelin) receptor, prompting the pituitary to release growth hormone in pulses, which raises IGF-1. Its distinguishing feature is that it is orally bioavailable, unlike the injectable peptide secretagogues. This describes the mechanism; the human trials below show what it does and does not achieve.
Is it FDA-approved?
Safety note
Status: Non-FDA-approved, investigational drug; a small molecule, not a peptide
Category: Wellness and performance · Primary body area: Bones & muscles
No. MK-677 is investigational and was never FDA-approved for any indication. It is not a legitimate dietary supplement (it is an unapproved drug) and is widely sold through gray-market channels. In sport, it is banned at all times, and WADA explicitly lists ibutamoren among prohibited growth hormone secretagogues. FDA's May 14, 2026 list places ibutamoren mesylate in 503A Category 2, bulk substances that raise significant safety risks.
What does the research show?
Editor’s note
Evidence strength: Moderate research (2 human · 0 animal/cell studies)
It has genuine multi-year human trials showing it raises growth hormone, IGF-1, and lean mass, but efficacy for meaningful functional outcomes is unproven, there are negative trials and metabolic safety signals, and it is not approved.
It has real human trials with a mixed picture. According to PubMed, two trials define it:
| Trial | Participants | Duration | Main finding |
|---|---|---|---|
| Nass 2008, randomized trial | 65 healthy adults aged 60 to 81 | 2 years | MK-677 raised growth hormone and IGF-1 |
| Sevigny 2008, trial | 563 people with mild to moderate Alzheimer's disease | 12 months | Raised IGF-1 but found no significant difference from placebo on any of 4 clinical scales |
In the Nass trial's first year, fat-free mass rose 1.1 kg on MK-677 and fell 0.5 kg on placebo (P < 0.001), but strength and function did not improve. Body weight rose 2.7 kg versus 0.8 kg on placebo, and fasting glucose rose 5 mg/dL. MK-677 was also associated with:
- Increased appetite
- Weight gain
- Mild fluid retention
- Higher fasting glucose
- Reduced insulin sensitivity
So it reliably raises growth hormone and lean mass, but without demonstrated functional benefit, with metabolic concerns, and with negative results for disease.
Sources: a 2-year trial in older adults (Nass et al., Annals of Internal Medicine, 2008, DOI: 10.7326/0003-4819-149-9-200811040-00003) and a 12-month Alzheimer's trial (Sevigny et al., Neurology, 2008, DOI: 10.1212/01.wnl.0000335163.88054.e7), indexed on PubMed; and the WADA Prohibited List. This document is educational, is not medical advice or a health claim, and is not an offer to sell any product.
Registered human trials
2 registered human trials on ClinicalTrials.gov that we reviewed
Sources
- [1]
- [2]
- [3]
- [4]
- PMID 19015485
- [5]
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