Ipamorelin was identified as the first truly selective GH secretagogue — it potently releases growth hormone without increasing cortisol, prolactin, or other hormones like older GHRP compounds do.
200x dose with no cortisol riseEven at 200 times the effective GH-releasing dose, ipamorelin did not increase cortisol, ACTH, or prolactin — unprecedented selectivity
What the researchers found
Ipamorelin released GH with potency similar to GHRP-6 but did not increase ACTH, cortisol, prolactin, or FSH even at doses 200-fold higher than effective GH-releasing doses, making it the first truly selective GH secretagogue.
Why it matters
Older GH-releasing peptides boosted cortisol and prolactin along with GH, limiting their therapeutic use. Ipamorelin's selectivity means it could stimulate growth hormone without these unwanted hormonal side effects.
How the study worked
Clinical pharmacology study describing ipamorelin's development from a chemistry program. Tested in vitro and in vivo including human subjects. GH, cortisol, ACTH, prolactin, and other hormones measured after various doses.
What this study cannot tell us
Clinical data available at time of publication was limited. Long-term safety and efficacy studies were not yet completed. Selectivity in healthy volunteers may differ from patient populations.
How to read the evidence
Strong evidence from comprehensive pharmacological characterization including human clinical data showing selectivity across a wide dose range.
When this study was published
Published in 1998. Ipamorelin has since become one of the most studied and commonly referenced GH secretagogues in the field.
The bigger picture
The quest for a clean GH-releasing agent has been a major goal in endocrinology. Ipamorelin's selectivity represented a breakthrough, showing it was possible to separate GH release from other hormonal effects. This principle has influenced all subsequent GH secretagogue development.
Questions still open
- What structural features give ipamorelin its selectivity?
- Does ipamorelin maintain selectivity during long-term use?
- Can ipamorelin treat GH deficiency states without the side effects of other secretagogues?
Common questions
Why is selectivity important for a GH peptide?
How does ipamorelin compare to GHRP-6?
Read the original research
Ipamorelin, the first selective growth hormone secretagogue.
European journal of endocrinology, 139(5), 552-61
Citation
Raun, K; Hansen, B S; Johansen, N L; Thøgersen, H; Madsen, K; Ankersen, M; Andersen, P H. (1998). Ipamorelin, the first selective growth hormone secretagogue.. European journal of endocrinology, 139(5), 552-61.