MK-677 vs Ipamorelin
Bottom line
Both work through the same receptor — the ghrelin receptor (GHS-R1a) — to make the pituitary release growth hormone, so both sit in the Growth Hormone Secretagogues class. The practical split is format and duration: MK-677 (ibutamoren) is an oral, non-peptide molecule with a ~24-hour action that sustains GH/IGF-1 all day, while Ipamorelin is an injectable peptide with a short (~2 h) pulse and a notably clean hormonal profile. MK-677 is the more clinically studied; Ipamorelin is the gentler, more pulsatile option. Neither is FDA-approved, and both are banned in sport.
At a glance
| MK-677 | Ipamorelin | |
|---|---|---|
| What it is | Non-peptide spiropiperidine (ghrelin mimetic) | Selective pentapeptide GHRP (ghrelin mimetic) |
| Receptor / mechanism | GHS-R1a (ghrelin receptor) → GH/IGF-1 | GHS-R1a (ghrelin receptor) → GH/IGF-1 |
| Route | Oral (pill) | Subcutaneous injection |
| Half-life / pattern | ~24 h — sustained daily elevation | ~2 h — brief GH pulse (peak ~40 min) |
| Typical dosing | ~25 mg once daily | ~100–300 µg, 1–3×/day (often with CJC-1295) |
| Evidence level | Clinical — human trials up to 2 years | Preclinical/Clinical — GH-release pharmacology; no efficacy RCTs |
| Hormonal selectivity | Ghrelin mimetic; increases appetite markedly | Selective — minimal cortisol/prolactin/appetite effect |
| FDA / legal status | Not approved (development discontinued); WADA S2 | Not approved (development discontinued); WADA S2 |
Key Differences
- Same pathway, different molecules. Unlike GHRH analogs (Sermorelin, CJC-1295), both MK-677 and Ipamorelin act on the ghrelin receptor. So combining them adds little mechanistically — the usual synergistic pairing is a GHRP + a GHRH analog (e.g., CJC-1295 + Ipamorelin), not two ghrelin mimetics.
- Oral vs injectable. MK-677’s non-peptide structure survives the gut, making it the only oral option in this class. Ipamorelin is a peptide destroyed by digestion, so it must be injected.
- Sustained vs pulsatile. MK-677’s ~24-hour half-life produces a continuous rise in GH/IGF-1; Ipamorelin’s short action mimics a discrete, physiologic pulse. Some consider the pulsatile pattern more natural; the sustained pattern is more convenient.
- Depth of evidence. MK-677 is the most clinically studied compound in this category — a 12-month trial (Nass 2008) showed it reliably raised IGF-1 and increased fat-free mass (+1.5 kg vs −0.5 kg placebo), but with no strength/function gain and worsened insulin sensitivity/glucose tolerance. Ipamorelin’s human data is essentially mechanistic/PK (selective GH release); there are no efficacy outcome trials.
- Side-effect profile. MK-677’s ghrelin action reliably increases appetite and is associated with water retention/edema and reduced insulin sensitivity (higher fasting glucose) — a meaningful metabolic consideration. Ipamorelin is described as the “gentle” GHRP: little appetite stimulation and minimal cortisol/prolactin effect, with mild flushing/water retention the usual complaints.
Which Is Which
- Convenience / oral dosing points to MK-677 — one pill a day, sustained IGF-1 — but with the trade-offs of appetite increase and glucose/insulin effects (monitoring is prudent).
- A cleaner, pulsatile profile points to Ipamorelin — though it requires injections and is usually paired with a GHRH analog (CJC-1295) to be worthwhile.
- They are not complementary with each other (same receptor); pairing a GHRP with a GHRH analog is the rationale-backed approach. See CJC-1295 + Ipamorelin.
- Both are unapproved and prohibited in and out of competition under the WADA Prohibited List (Section S2). Long-term safety is unestablished for both. See Regulatory & Legal Status and Evidence Grading Explained.
Not medical advice — See Disclaimer.
References
- Nass R. et al. (2008). “Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults: a randomized trial” (MK-677, 25 mg/day, 12 months). Annals of Internal Medicine.
- Raun K. et al. (1998). “Ipamorelin, the first selective growth hormone secretagogue.” European Journal of Endocrinology, 139(5):552–561.
- Ishida J. et al. (2020). “Growth hormone secretagogues: history, mechanism of action, and clinical development.” JCSM Rapid Communications.
- WADA (2026). Prohibited List, Section S2 (peptide hormones, growth factors, related substances and mimetics).
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