GHRP-2 vs GHRP-6

Side by side

GHRP-2 Medium and GHRP-6 Medium are synthetic peptides that act on the growth hormone secretagogue receptor, the receptor ghrelin uses, and both are named in S2.2.4 of WADA's 2026 List ¹. They were developed in the same era and are often grouped together, but their histories diverged. The table is read from our encyclopedia entries.

GHRP-2: from laboratory peptide to diagnostic test

GHRP-2 is the one that became a product, in one country and for one purpose. According to our entry, it is approved in Japan only, as pralmorelin, a single-dose intravenous test for growth hormone deficiency ¹. Its validation study gave 100 micrograms intravenously after an overnight fast to 77 healthy adults and 58 patients with severe deficiency by the insulin tolerance test; growth hormone peaked within 60 minutes in everyone, at 84.6 µg/L on average in the healthy group ². It has also been studied as a test for adrenal failure: a peak cortisol below 11.6 µg/dL after GHRP-2 predicted secondary adrenal insufficiency with 89.7% sensitivity and 88.9% specificity ³.

Outside diagnosis, a trial in men with prolonged critical illness found that a continuous GHRP-2 infusion reactivated growth hormone secretion and normalised IGF-1 and its binding proteins ⁴. And in lean healthy men, a GHRP-2 infusion before a buffet meal raised food intake by 35.9%, with every participant eating more ⁵.

GHRP-6: a research tool that stayed one

GHRP-6's studies are mostly 1990s endocrine experiments. In healthy men, overnight intravenous doses raised growth hormone to an average of 15.4 ng/mL against 5.5 on placebo, and also raised ACTH and cortisol ⁶. Taken by mouth by short children, it raised growth hormone close to the response to the maximally effective intravenous dose ⁷. Assessed as a test of pituitary reserve in children, its responses overlapped too much between deficient and normal children to diagnose individuals ⁸, which may help explain why GHRP-2, not GHRP-6, became the diagnostic. According to our entry, GHRP-6 was never approved anywhere, and the FDA lists it in 503A Category 3 and 503B Category 2 ¹.

Where GHRP-6 still worked

GHRP-6's most interesting human results come from conditions in which the GHRH route falters. In 11 people with an underactive thyroid, GHRH released far less growth hormone than in controls (peak 4.1 against 24.9 µg/L), while GHRP-6 did better (12.6 against 22.1) ⁹. In patients with cortisol excess, from disease or from glucocorticoid drugs, GHRH barely worked, but GHRP-6 still released growth hormone ¹⁰. These studies show the two receptor routes behaving differently in disease; they did not lead to a treatment, and the same receptor action underlies GHRP-2's use as a diagnostic.

What they share: appetite and stress hormones

Both raise more than growth hormone. GHRP-6's rise in ACTH and cortisol is documented in healthy men ⁶, and GHRP-2's cortisol response is strong and consistent enough to be used as a diagnostic for adrenal failure ³. The appetite effect documented for GHRP-2 ⁵ fits their shared action on the ghrelin receptor. That is the main contrast with ipamorelin, which in animal studies released growth hormone without raising ACTH or cortisol; our ipamorelin vs GHRP-6 comparison covers that difference.

How the differences add up (as of October 3, 2026)

GHRP-2 has the stronger human record and a narrow approval in Japan as a diagnostic; GHRP-6 has a longer list of small physiological studies and no approval anywhere. Neither is approved in the US, and neither has evidence for the long-term body-composition or anti-ageing uses they are sold for. Our three-way comparison with hexarelin adds desensitisation and hunger. Both are prohibited at all times in sport ¹. Doses on this page are those in our entries' sources, not recommendations.

Frequently asked questions

What is the difference between GHRP-2 and GHRP-6?

Both release growth hormone through the ghrelin receptor and raise cortisol. GHRP-2 is approved in Japan as pralmorelin, a diagnostic test for growth hormone deficiency; GHRP-6 was never approved.

Does GHRP-2 increase appetite?

In one study of lean men, a GHRP-2 infusion raised food intake at a buffet meal by 35.9%.

Are GHRP-2 and GHRP-6 legal?

Neither is FDA-approved; GHRP-6 cannot be compounded in the US, and both are banned in sport under WADA's S2.2.4.

Related on Grey Peptides

• GHRP-2
• GHRP-6
• Ipamorelin vs GHRP-6

Sources

1. Grey Peptides dataset records for both compounds (status, half-life and studied doses as sourced on each entry); read October 2, 2026.
2. Chihara, K., et al. (2007). A simple diagnostic test using GH-releasing peptide-2 in adult GH deficiency. Eur J Endocrinol, 157(1), 19-27. PMID: 17609397
3. Arimura, H., et al. (2016). Investigation of the clinical significance of the growth hormone-releasing peptide-2 test for the diagnosis of secondary adrenal failure. Endocr J, 63(6), 533-44. PMID: 27020037
4. Van den Berghe, G., et al. (2002). The combined administration of GH-releasing peptide-2 (GHRP-2), TRH and GnRH to men with prolonged critical illness evokes superior endocrine and metabolic effects compared to treatment with GHRP-2 alone. Clin Endocrinol (Oxf), 56(5), 655-69. PMID: 12030918
5. Laferrère, B., et al. (2005). Growth hormone releasing peptide-2 (GHRP-2), like ghrelin, increases food intake in healthy men. J Clin Endocrinol Metab, 90(2), 611-4. PMID: 15699539
6. Frieboes, R. M., et al. (1995). Growth hormone-releasing peptide-6 stimulates sleep, growth hormone, ACTH and cortisol release in normal man. Neuroendocrinology, 61(5), 584-9. PMID: 7617137
7. Bellone, J., et al. (1995). Growth hormone-releasing effect of oral growth hormone-releasing peptide 6 (GHRP-6) administration in children with short stature. Eur J Endocrinol, 133(4), 425-9. PMID: 7581965
8. Pombo, M., et al. (1996). Growth hormone releasing hexapeptide-6 (GHRP-6) test in the diagnosis of GH-deficiency. J Pediatr Endocrinol Metab, 9 Suppl 3, 333-8. PMID: 8887178
9. Pimentel-Filho, F. R., et al. (1997). Growth hormone responses to GH-releasing peptide (GHRP-6) in hypothyroidism. Clin Endocrinol (Oxf), 46(3), 295-300. PMID: 9156038
10. Borges, M. H., et al. (1997). Different effects of growth hormone releasing peptide (GHRP-6) and GH-releasing hormone on GH release in endogenous and exogenous hypercortisolism. Clin Endocrinol (Oxf), 46(6), 713-8. PMID: 9274702

Educational information, not medical advice. Each dose in this guide names its source, an approved label or a published study. None is a recommendation for you. An unapproved compound has no established safe or effective human dose, and products sold for “research use only” are not made or tested for people. Talk to a doctor before acting on anything on this site, including before you start, stop or change any medicine or dose.