What Is GHRP-6? Structure, Discovery and Status

GHRP-6 is a synthetic six-residue peptide, His-D-Trp-Ala-Trp-D-Phe-Lys-NH2, described in 1984 as acting on the pituitary to release growth hormone specifically [1]. Its formula is C46H56N12O6, its molecular weight about 873.0 Da and its CAS number 87616-84-0. It acts on the growth hormone secretagogue receptor 1a, the receptor later found to respond to the natural hormone ghrelin.

Why does GHRP-6 matter historically?

GHRP-6 came first. Its activity implied a receptor distinct from that of growth hormone-releasing hormone, the receptor was cloned in the 1990s, and the natural ligand, ghrelin, was identified only after that. The investigator behind the original peptides later reviewed that sequence of discoveries [2].

What does its structure look like?

The peptide was designed from earlier enkephalin analogs. It contains two D-residues, D-tryptophan and D-phenylalanine, which resist enzymatic breakdown, two tryptophans that absorb ultraviolet light strongly, and a C-terminal lysine amide shared by the whole family.

What is its status?

GHRP-6 is not approved as a medicine in the United States. As of April 2026 it is on the FDA list of bulk drug substances that may present significant safety risks in compounding [3].

How is it identified in the laboratory?

By mass spectrometry against 873.0 Da and by HPLC purity; its two tryptophans make detection sensitive. Tryptophan can oxidize, adding 16 or 32 Da, so oxidized forms are a common impurity in aged material.

Frequently asked questions

Is GHRP-6 the same as ghrelin?

No. Ghrelin is a natural 28-residue hormone; GHRP-6 is a synthetic hexapeptide that acts on the same receptor.

How does GHRP-6 differ from GHRP-2?

GHRP-2 replaces the first two residues with D-alanine and D-2-naphthylalanine and weighs about 818.0 Da.

Does FLASK list GHRP-6?

Yes, as GHRP-6 5 mg, with structure data on the product page.