Compound family

GH secretagogues (GHRPs)

In one sentenceGhrelin-receptor agonists that trigger a growth-hormone pulse. Good diagnostic tools — and one oral member, MK-677, with a year-long trial showing a little more lean mass and no less fat.
Compounds5
Best gradeB MK-677 (ibutamoren)
Approved medicines1 of 5
Prohibited in sport5 of 5

What this family is

The growth-hormone-releasing peptides mimic ghrelin, the stomach hormone, at its receptor in the pituitary and hypothalamus. GHRP-6 was the first, GHRP-2 followed, hexarelin is the most potent, and ipamorelin was designed to be selective — a strong growth-hormone pulse with little effect on cortisol or prolactin. All four peptides raise growth hormone measurably and reliably in single-dose studies; GHRP-2 is approved in Japan as a diagnostic test on exactly that basis. MK-677, ibutamoren, is the odd one out: a small molecule that does the same job by mouth, and the only member with a year-long randomised trial.

That is where the peptides' evidence stops. MK-677's 65-person trial in older adults found about 1.1 kg more fat-free mass than placebo over a year, no change in total or visceral fat, and more appetite — a real result, and a modest one. Ipamorelin's only randomised trial tested it for post-operative gut recovery in 117 patients and found no benefit; development ended. Hexarelin's one study of continued use found the growth-hormone response fades within weeks and body composition did not change. GHRP-2 and GHRP-6 also stimulate appetite, which is measurable, and have no trial of the muscle-building or fat-loss use they are sold for.

Every member is prohibited in sport at all times. None is an approved medicine for any therapeutic use; MK-677's development was abandoned after a negative Alzheimer's trial.

Grade counts across the family: 0 × A · 1 × B · 4 × C · 0 × D. The best grade here, B, means probable, not settled. How LYO grades →

The compounds, graded

Every member with its best-supported outcome grade, human-trial count and regulatory status. Each opens the full evidence page.

MK-677 (ibutamoren)

B

An oral, non-peptide growth-hormone secretagogue — the one with a year-long randomised trial, which found more lean mass and no less fat.

Human trials2 large RCTs (n=65 over 2 yr; n=563 over 1 yr) + small studies
StatusNot approved

Ipamorelin

C

Selective GH secretagogue. One real randomised trial in humans — and it was negative.

Human trials1 RCT (negative) + small early-phase
StatusNot approved

GHRP-2

C

A GH-releasing peptide approved in Japan as a diagnostic — not as the muscle drug it is sold as.

Human trialsDiagnostic-grade + small studies
StatusApproved (diagnostic, Japan)

GHRP-6

C

The original GH-releasing peptide — a good diagnostic tool, an unproven physique drug.

Human trialsDiagnostic studies + small work
StatusNot approved

Hexarelin

C

A potent GH-releasing peptide whose effect fades with continued use — and that was never developed further.

Human trialsEarly-phase human studies
StatusNot approved

Comparisons

Questions

Is ipamorelin the safest GH secretagogue?
It is the most selective in pharmacology — the growth-hormone pulse comes with little cortisol or prolactin. Selectivity in a single-dose study is not a safety record; long-term use has not been studied in any of them.
Do GHRPs build muscle?
No controlled trial in healthy adults has shown it for the peptides. MK-677, the oral member, raised fat-free mass by about 1.1 kg over a year in adults over 60 — lean tissue, not measured strength — while leaving fat unchanged. That is the only body-composition trial in the family.
Why does hexarelin stop working?
Tolerance: in the one study of repeated dosing, the growth-hormone response fell over a few weeks. That finding is a large part of why the compound was never developed further.

Written and maintained by LYO Research — how pages are written and checked. Reviewed 23 September 2026. Grades count human evidence only. Not medical advice. Correct this page →