MK-677 vs GHRP-2 — Non-Peptide Oral vs Peptide Injectable Ghrelin-Receptor Agonists
MK-677 (ibutamoren, oral non-peptide) vs GHRP-2 (pralmorelin, injectable peptide): shared receptor target, different chemistry, different regulatory status. UK research-literacy comparison.
| Feature | MK-677 | GHRP-2 |
|---|---|---|
| Chemical class | Non-peptide small molecule (piperidine derivative) | Synthetic hexapeptide |
| Receptor | GHS-R1a (ghrelin receptor) | GHS-R1a (ghrelin receptor) |
| Route | Oral (bioavailable) | Subcutaneous / intranasal (peptide, poor oral bioavailability) |
| Half-life | ~4-6 hours | ~30-45 minutes |
| GH-secretion pattern | Amplified pulsatile GH release (physiological pattern) | Amplified pulsatile GH release (physiological pattern) |
| IGF-1 elevation | Sustained IGF-1 rise into younger-adult range (Chapman 1996) | Transient GH pulse; IGF-1 rise depends on dose frequency |
| Landmark human trial | Chapman 1996 JCEM — elderly healthy adults, sustained GH/IGF-1 amplification | Furuta 2004 (pharmacology overview); regulatory use only in Japan for GH-deficiency diagnostic testing |
| Bone-turnover evidence | Yes (Murphy 1999 J Bone Miner Res) — markers ↑ in elderly adults | Limited standalone bone data |
| Approved indication | None — Merck development discontinued | Japan only — pralmorelin as GH-deficiency diagnostic (KP-102) |
| UK MHRA status | Not licensed — research chemical | Not licensed — research chemical |
| WADA status | Prohibited (S2.2 — GH secretagogues) | Prohibited (S2.2 — GH secretagogues) |
| Dosing cadence in research | Once daily (long half-life) | Multiple daily (short half-life) |
Mechanism differentiation
Both compounds activate the same receptor — GHS-R1a, the ghrelin receptor. Both amplify pulsatile GH release rather than driving a sustained non-pulsatile GH signal (which is what exogenous recombinant GH produces). The difference between them is chemistry, not pharmacology at the receptor.
MK-677 is a small-molecule piperidine derivative. Its oral bioavailability and 4-6 hour half-life make daily oral dosing practical. That property was what motivated Merck's development programme in the 1990s — GH-deficiency and osteoporosis indications wanted a once-daily oral option.
GHRP-2 is a synthetic hexapeptide. Poor oral bioavailability (typical of peptides), short (~30-45 minute) plasma half-life. In clinical research, that meant multi-daily subcutaneous or intranasal dosing. In Japan, pralmorelin reached limited licensed use as a diagnostic agent (KP-102, "Kaken 102") for the standard GH-deficiency stimulation test — a single-dose diagnostic use, not a chronic therapy.
Evidence base
Neither compound has a modern outcomes-trial evidence base — both peaked in clinical research in the late 1990s to early 2000s.
MK-677 landmark trials: Chapman 1996 (GH/IGF-1 axis stimulation in elderly), Murphy 1998 (catabolism reversal), Murphy 1999 (bone-turnover markers), Murphy 2001 (osteoporosis — negative on BMD). The negative BMD result contributed to Merck discontinuing the programme.
GHRP-2 evidence: primarily pharmacology and PK studies, plus the Japanese diagnostic-agent development. No modern outcomes trials. WADA-monitored via urinary metabolite detection.
Regulatory context
Neither is a licensed medicine in the UK. Both are on the WADA prohibited list (S2.2 category — GH secretagogues). Both are sold as "research chemicals" via online supplement / grey-market channels, none of which have regulatory sanction for human use.
Advertising either compound for human use in the UK falls under MHRA rules for unlicensed-medicine advertising — see the POM advertising hub.
Related pages
- MK-677 monograph
- GHRP-2 monograph
- Ipamorelin monograph — selective peptide GHS comparator
- GH axis mechanism map
- Peptides and sports anti-doping
Verdict — research-question matching
Same receptor target, but effectively different tools. MK-677's oral bioavailability and once-daily dosing made it a viable candidate for chronic indications like osteoporosis; when the osteoporosis programme did not produce a licensable BMD gain, its development stopped. GHRP-2 is a research peptide that reached limited licensed use only as a GH-deficiency diagnostic (Japan). Neither is a UK medicine. Both are WADA-prohibited. A UK reader looking at either compound is looking at published mechanism and PK research on an unapproved product — not at anything with a UK regulatory pathway.
References
Peer-reviewed sources for the claims above. Where an editor has verified study type, sample size, outcome and limitation, the citation is rendered as a card; otherwise as a plain reference. Links open PubMed or the journal DOI.
- Chapman IM, Bach MA, et al.. Stimulation of the growth hormone (GH)-insulin-like growth factor I axis by daily oral administration of a GH secretogogue (MK-677) in healthy elderly subjects. Journal of Clinical Endocrinology and Metabolism. 1996;81(12) :4249-4257 · PMID: 8954023
- Murphy MG, Bach MA, et al. (MK-677 Study Group). Oral administration of the growth hormone secretagogue MK-677 increases markers of bone turnover in healthy and functionally impaired elderly adults. Journal of Bone and Mineral Research. 1999;14(7) :1182-1188 · PMID: 10404019
- Sigalos JT, Pastuszak AW. The Safety and Efficacy of Growth Hormone Secretagogues. Sexual Medicine Reviews. 2018;6(1) :45-53 · PMID: 28400207
- n/a. Pralmorelin: GHRP 2, GPA 748, growth hormone-releasing peptide 2, KP-102 D, KP-102 LN, KP-102 D-LN. Drugs in R&D. 2004;5(4) :236-239 · PMID: 15230633
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