Hexarelin is a synthetic hexapeptide secretagogue, more potent than GHRP-6 at releasing growth hormone. It is included partly because its most interesting research literature has nothing to do with GH.

Hexarelin binds CD36 in addition to the ghrelin receptor, and a body of cardiovascular work explores effects on cardiac function that appear to be independent of growth hormone entirely. That work is preclinical and has not produced a clinical programme, but it is a better reason to find the compound interesting than the GH story.

Potent GHS-R1a agonism producing GH release, with cortisol and prolactin effects intermediate between GHRP-6 and the selective agents.

Separately, it binds the scavenger receptor CD36, which is expressed in cardiac tissue and macrophages. Animal work reports cardioprotective effects in ischaemia models that persist in GH-deficient animals, implying a GH-independent pathway.

Tachyphylaxis is marked: the GH response attenuates substantially with repeated dosing over weeks, which limits its usefulness as a sustained GH strategy regardless of anything else.

Preclinical for the cardiac work, early clinical for the endocrine work. Human studies established potent GH release and characterised the attenuation of that response with continued administration.

No clinical outcome trial has been completed for any indication. The cardiac literature is animal work that has not translated, which after two decades is itself informative.

Short human exposure reported flushing, transient hypertension and effects on cortisol and prolactin. Tachyphylaxis means that sustained use produces diminishing endocrine effect while whatever risks exist continue.

No long-term human safety data. Prohibited in sport under WADA's S2 category, and sold as an unverified research chemical.

Never approved. Research chemical, prohibited in sport.