Created during growth hormone secretagogue research. Studied as a more targeted approach within the category.
Ipamorelin
Ipamorelin is a synthetic pentapeptide that acts as a growth hormone secretagogue at the ghrelin receptor. It was characterised in the late 1990s at Novo Nordisk and described in the literature as the first selective compound in its class.
Selectivity is the whole story. Earlier secretagogues stimulated growth hormone release but also affected cortisol and prolactin, which complicated interpretation of any result. Ipamorelin was reported to produce growth hormone release without those accompanying changes, which made it valuable as a research tool independently of any application: a cleaner instrument for isolating one variable.
The defining paper is Raun and colleagues in the European Journal of Endocrinology in 1998, characterising selectivity against comparator compounds in animal models. Subsequent work has examined the ghrelin receptor system more broadly. Ipamorelin is frequently studied alongside a GHRH analogue such as CJC-1295, because the two act on different pituitary pathways.