A non-peptide, orally active growth hormone secretagogue that mimics ghrelin at the GHS-R1a receptor. Technically not a peptide (it's a small molecule), but included here because it targets the same ghrelin receptor as peptide GH secretagogues and is commonly discussed alongside them. Produces sustained 24-hour GH and IGF-1 elevation from a single oral dose.
MK-677 (ibutamoren mesylate) is a non-peptide, orally active growth hormone secretagogue developed by Merck. While it is not technically a peptide, it is universally discussed alongside peptide GH secretagogues because it targets the same ghrelin receptor (GHS-R1a) and produces similar effects.
MK-677's key advantage over peptide GHRPs is its oral bioavailability — patients take a pill instead of injecting. A single 25mg oral dose produces sustained GH pulsatility and IGF-1 elevation for a full 24 hours, making it the most convenient GH-optimizing compound available.
MK-677 (ibutamoren) occupies a unique position in the GH secretagogue landscape: it is the only orally bioavailable growth hormone secretagogue, eliminating the need for injections that all peptide-based secretagogues require. This oral availability, combined with its long duration of action (~24 hours), made it the most widely used growth hormone-elevating compound in the biohacking and longevity communities before increased regulatory scrutiny.
Technically, MK-677 is a non-peptide small molecule — it's a peptidomimetic that mimics the structure of ghrelin enough to activate the GHS-R1a receptor, but its molecular structure is not a peptide chain. It was developed by Merck and progressed through multiple clinical trials (including studies in elderly patients with hip fractures and GH-deficient adults) but was never brought to market approval.
MK-677 produces sustained 24-hour elevation of GH and IGF-1 levels after a single oral dose, with IGF-1 increases of 40-97% reported in clinical studies. The sustained elevation (rather than the pulsatile release produced by injectable secretagogues like ipamorelin) is both an advantage (convenience) and a potential concern (chronic GH elevation may carry different risks than pulsatile elevation).
MK-677 activates the same GHS-R1a receptor as peptide GHRPs but with distinct pharmacokinetics. Its oral bioavailability and sustained receptor occupancy produce continuous GH pulse amplification rather than the single bolus effect of injected peptides. This more closely mimics the physiological GH secretion pattern of a younger individual.
| Pathway | Effect | Significance |
|---|---|---|
| Oral GHS-R1a agonism | Sustained receptor activation from oral dosing | 24-hour GH pulsatility from single daily dose |
| IGF-1 elevation | 40-90% increase in IGF-1 maintained for months | Anabolic, body composition, and recovery effects |
| No desensitization | Unlike hexarelin, IGF-1 elevation maintained for 12+ months | Suitable for long-term use |
| Appetite increase | Moderate ghrelin-mimetic hunger | Less intense than GHRP-6 but more than ipamorelin |
| Sleep improvement | Increases duration of stage 3/4 (deep) NREM sleep | GH is primarily released during slow-wave sleep |
| Study | Design | Findings | Level |
|---|---|---|---|
| IGF-1 elevation | Phase II, n=187, 2 years | 25mg/day increased IGF-1 by ~40% sustained over 2 years with no tachyphylaxis | Level II |
| Body composition | Clinical studies | Increased lean mass (~1.8 kg) and trend toward decreased fat mass over 8 weeks | Level II |
| Bone density | Phase II, elderly | Increased bone mineral density in postmenopausal women after 18 months | Level II |
| Sleep quality | Clinical studies | Increased REM and stage 4 sleep duration by ~50% | Level II |
| Sarcopenia | Phase II, elderly | Improved physical function and lean mass in elderly hip fracture patients | Level II |
Appetite stimulation: MK-677 significantly increases appetite in most users — a direct consequence of ghrelin-receptor activation. This is the most commonly reported side effect and can be counterproductive for individuals using it during caloric restriction or weight loss protocols.
Water retention and edema: Dose-dependent water retention is common, particularly during the first 2-4 weeks. Some patients experience significant peripheral edema. This is a GH-mediated effect and may require dose reduction.
Blood glucose and insulin resistance: Chronic GH elevation can impair glucose tolerance and increase insulin resistance. Clinical studies showed fasting glucose increases of 5-10 mg/dL in some participants. Patients with pre-diabetes or diabetes should exercise particular caution, and regular glucose monitoring is recommended.
Sleep quality: Some users report improved sleep quality (particularly deeper sleep stages), which is consistent with the known relationship between GH secretion and slow-wave sleep. However, vivid dreams and, less commonly, sleep disturbances have also been reported.
Long-term data: MK-677 has the most extensive long-term human safety data of any GH secretagogue, with published studies of up to 2 years duration. In these studies, sustained IGF-1 elevation was maintained without tachyphylaxis (loss of effect), and no serious drug-related adverse events were reported.
| Jurisdiction | Status |
|---|---|
| FDA | Not approved. Merck discontinued development after Phase II. |
| WADA | Banned under S2 (peptide hormones and growth factors — despite being non-peptide, it targets the same pathway) |
| Availability | Widely available as a research chemical. One of the most popular GH-related compounds in biohacking communities. |