Ipamorelin: why it was called the first selective GH secretagogue

Ipamorelin acts on the ghrelin receptor (GHS-R1a). What made it notable in 1998 was selectivity: in the animal studies it raised growth hormone without the cortisol and prolactin rises seen with earlier secretagogues like GHRP-6. Key papers: 1. Raun et al. (Eur J Endocrinol, 1998), the original selectivity study. https://doi.org/10.1530/eje.0.1390552 2. Ahnfelt-Rønne et al. (Endocrine, 2001), comparing GH-releasing peptides at the ghrelin receptor. https://doi.org/10.1385/ENDO:14:1:133 3. Andersen et al. (Growth Horm IGF Res, 2001), on ipamorelin in bone research. https://doi.org/10.1054/ghir.2001.0239 Ipamorelin reached Phase 2 human trials for post-surgical gut recovery but was not developed further. For discussion: does the selectivity seen in rats hold up in the later data? The full write-up is in Guides: Ipamorelin.