Ipamorelin vs GHRP-2 vs GHRP-6: Growth Hormone Secretagogues Compared

Ipamorelin, GHRP-2 and GHRP-6 are synthetic peptides that act on the same target, the growth hormone secretagogue receptor 1a, also called the ghrelin receptor. They differ in length, sequence and selectivity. GHRP-6 is a hexapeptide described in 1984 [1]; GHRP-2, also called pralmorelin, is a related hexapeptide; Ipamorelin is a pentapeptide described in 1998 as the first selective member of the family [2].

How do the three structures differ?

GHRP-6 is His-D-Trp-Ala-Trp-D-Phe-Lys-NH2, about 873.0 Da. GHRP-2 replaces the first two residues with D-alanine and D-2-naphthylalanine, giving D-Ala-D-2Nal-Ala-Trp-D-Phe-Lys-NH2 at about 818.0 Da. Ipamorelin is shorter: Aib-His-D-2Nal-D-Phe-Lys-NH2, about 711.9 Da. All three end in lysine amide and contain D-amino acids that resist enzymatic breakdown.

What does selective mean here?

In animal studies, GHRP-6 and GHRP-2 increased growth hormone but also adrenocorticotropic hormone and cortisol. Ipamorelin was reported to increase growth hormone without comparable increases in those hormones, which is why its developers called it selective [2]. The distinction comes from animal pharmacology and should be read in that context.

What is the regulatory status of each?

None of the three is approved as a medicine in the United States. Pralmorelin has been used in Japan as a diagnostic agent for testing growth hormone secretion, and clinical reports from that setting exist [3]. As of April 2026, GHRP-2, GHRP-6 and ipamorelin acetate are all on the FDA list of bulk drug substances that may present significant safety risks in compounding [5]. GHRP-2 and its metabolite are also targets of anti-doping urine analysis [4].

How are they identified in the laboratory?

Their masses are distinct enough that mass spectrometry separates all three. Each contains aromatic residues, tryptophan or naphthylalanine, so HPLC detection is straightforward. Because D- and L-residues have identical masses, stereochemical purity requires a chiral method.

Frequently asked questions

Is GHRP-2 the same as pralmorelin?

Yes. Pralmorelin is the nonproprietary name of GHRP-2.

Are these peptides related to ghrelin?

They act on the ghrelin receptor but are not fragments of ghrelin; GHRP-6 was in fact described years before ghrelin itself was identified.

Does FLASK list all three?

Yes: GHRP-2 (10 mg), GHRP-6 (5 mg) and Ipamorelin (5 mg), each with structure data on the product page.