Research Commentary
Ipamorelin’s selectivity was a receptor finding, not a body-composition result
Raun and colleagues called ipamorelin the first selective growth hormone secretagogue. Selectivity against cortisol and prolactin is not proof of a clinical outcome.
The growth hormone secretagogue story starts with Bowers and the GHRP series, peptides that release growth hormone and, inconveniently, often move cortisol and prolactin as well. Ipamorelin was published by Raun and colleagues in 1998 as the selective one: growth hormone release with much less of that companion hormone rise, in the models they used. That paper is why the word “selective” is glued to the name.
Selective compared with what
Compared with earlier secretagogues, in the assays and animal experiments of that era. Not compared with exercise, sleep, or an approved growth-hormone prescription in a modern outcome trial. GHRP-2 and GHRP-6 remain different peptides with their own receptor behavior. Blends that combine a GHRH analogue with ipamorelin are a third design again. A 1998 selectivity paper does not describe those blends.
The safety review is the sober companion
Sigalos and Pastuszak, in Sexual Medicine Reviews, surveyed the safety and efficacy claims around growth hormone secretagogues, including ipamorelin, CJC-1295, and the GHRPs. Their usefulness is the tone: interest in the pharmacology, and a refusal to pretend the clinical file matches the marketing. This journal takes the same stance. Link Raun for the pharmacology. Do not let “selective” do the work of a trial that has not been run.