MK-677
Growth hormone In trials Human trials
Also called Ibutamoren, Ibutamoren mesylate, L-163,191
Not a peptide, but it acts on the same receptor as the peptide growth hormone secretagogues. It is an orally active ghrelin receptor agonist, which is unusual: most of this class must be injected. A single daily capsule raises growth hormone and IGF-1 for about 24 hours.
Evidence at a glance
- Evidence
- Human trials — Studied in people
- Status
- Reached clinical trials
- Dosing
- A dose has been tested in humans
Despite good trial data it was never approved — development stopped. It raises blood glucose and reduces insulin sensitivity, and the fat-free mass it adds includes water. Sustained IGF-1 elevation carries the same theoretical cancer concern as other growth signalling.
What studies report
- Raised IGF-1 in older adults to levels typical of young adults in a 2-year trial
- Increased fat-free mass by about 1.1 kg versus placebo in that trial
- Did not reduce fat mass, unlike injected secretagogues
- Trialled for hip-fracture recovery and muscle wasting
How it works
Agonist at the ghrelin receptor (GHS-R1a) — the same target as GHRP-2, GHRP-6 and ipamorelin — but orally bioavailable and long-acting.
Where it acts
Pituitary glandThe library groups this compound under Growth hormone. The diagram shows that target, not every tissue it reaches.
Illustrated
AI-generated subject illustration; not a depiction of the compound or evidence of its effects.
Why people take it
Reasons people seek it out — not a list of proven effects.
In practice Unapproved use
- Popular precisely because it is oral and once daily
- Water retention and increased appetite are commonly reported
- Often run in cycles rather than continuously, over concerns about sustained IGF-1 elevation
Reported real-world use, not evidence and not a recommendation.
Dosing
What was tested Evidence
- 25 mg daily, oral2 yearsTrial in healthy older adults→ IGF-1 restored to young-adult levels; +1.1 kg fat-free mass; no fat loss
- 25 mg daily, oralUp to 24 weeksHip fracture recovery trial→ Improved gait speed in some measures
What people report using Not evidence
- 12.5–25 mg once daily, on an empty stomach
- Often cycled over concerns about sustained IGF-1 elevation
Reported for reference, not as instruction. Nothing here is a recommendation to take anything, and most of these compounds are not approved for human use.
Status: Reached phase 2 and 3 trials for several indications. Never approved; development discontinued.
- Route
- Oral capsule — a small molecule, so digestion is not a barrier
- Formula
- C27H36N4O5S
- Molecular weight
- 528.7 g/mol
- CAS
- 159752-10-0
- Available as
- 25 mg capsules
Search PubMed for MK-677 → We link a live search rather than a fixed citation list, so it stays current and nothing here is a reference we have not checked.
Compared with
Side-by-side pages for the compounds this one is most often confused with or taken alongside.
Educational information only. Nothing here is medical advice, a dosing protocol, or a recommendation to use any compound. Most entries describe substances not approved for human use. Talk to a licensed clinician before acting on anything you read here. How to read these entries.