GHRP-2 vs GHRP-6

Two near-identical growth-hormone-releasing peptides — is there any real difference?

No head-to-head trial — cross-trial comparison
In one paragraphBoth are six-amino-acid ghrelin mimics that reliably raise growth hormone, and both perform well enough as a diagnostic stimulus to substitute for the insulin tolerance test. GHRP-2 is approved in Japan for exactly that purpose and has the better-quantified appetite data; GHRP-6 is the older molecule and drives hunger more prominently. Neither has a controlled trial for muscle, fat or body composition, and both are banned in sport.

Side by side

C GHRP-2C GHRP-6
LYO overall gradeCC
Approved anywhereYes — Japan, as a diagnostic (pralmorelin)No
Diagnostic performancePeak GH 1.36 vs 84.6 µg/l, deficient vs healthyAs sensitive and specific as the insulin tolerance test
Appetite effect+35.9% food intake in healthy men (n=7)Increases hunger; less well quantified
Body-composition evidenceNoneNone
SelectivityRaises cortisol and prolactin more than ipamorelinRaises cortisol and prolactin; the least selective of the group
Reported side effects (diagnostic dose)FlushingFlushing only
Sport (WADA)Prohibited at all times (S2)Prohibited at all times (S2)
Verdict

For the one use either is genuinely evidenced — provoking a measurable growth-hormone response for diagnosis — GHRP-2 has the formal approval. For everything they are actually sold for, the evidence is identical: none.

The same molecule class, a decade apart

GHRP-6 came first, and the work that produced it led to the discovery of ghrelin and its receptor — a genuine contribution to endocrinology. GHRP-2 followed as a refinement: slightly more potent at releasing growth hormone for a given dose, and the one that a pharmaceutical company took far enough to earn an approval.

Functionally they are close cousins. Anyone claiming a large practical difference between them for physique purposes is describing something no trial has measured.

The use that is actually evidenced

Testing whether someone's pituitary can release growth hormone traditionally means an insulin tolerance test, which deliberately induces hypoglycaemia and is dangerous for people with epilepsy or heart disease. A GH-releasing peptide does the same job without that risk, which is why both were studied as diagnostic agents.

GHRP-2 separates the groups cleanly: peak growth hormone averaged 1.36 µg/l in deficient patients against 84.6 in healthy controls. GHRP-6, tested against the insulin tolerance test directly, was found to be as sensitive and specific for diagnosing adult GH deficiency. This is real, useful, approval-grade work — and it involves a single injection, not a course.

Hunger is the difference people notice

Because they mimic ghrelin, both increase appetite. That effect is best quantified for GHRP-2: healthy men infused with it ate 35.9% more at a buffet meal than on saline, with every participant increasing intake. GHRP-6 is generally described as the hungrier of the two, though the human data behind that comparison are thinner.

For someone using these to gain weight, the appetite effect may be doing more of the work than the growth hormone. No trial has separated the two.

Questions people actually ask

Which is stronger?
GHRP-2 is more potent at releasing growth hormone per dose. Neither has been shown to produce a clinical outcome, so 'stronger' refers only to the hormone marker.
Do they build muscle?
No controlled human trial has tested either for muscle or body composition. The claim is extrapolated from an acute growth-hormone rise.
Is GHRP-2 legal because Japan approved it?
Japan approved pralmorelin as a diagnostic agent — a single injection to test pituitary function. That is not an approval for repeated use, and it does not apply outside Japan. Both are prohibited in sport at all times.

References

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