Ipamorelin: Selective Growth Hormone Secretagogue Pharmacology

The selectivity result

Raun et al. (Eur J Endocrinol, 1998) titled their paper "Ipamorelin, the first selective growth hormone secretagogue," and that framing is the compound's defining characteristic. Earlier growth hormone-releasing peptides also stimulated ACTH and cortisol release, which limited their usefulness as experimental tools because the growth hormone effect could not be isolated.

The selectivity claim is the reason ipamorelin remains in use in research contexts. If the objective is to stimulate endogenous growth hormone release without confounding adrenal axis activation, this is the compound with the clearest supporting result.

Note that GHS-R1a is the ghrelin receptor, so this is agonism at a receptor with its own physiology including appetite and gastric motility effects. Selectivity in the 1998 sense refers to the hormone release profile, not to receptor exclusivity.

Foundational pharmacology

Ankersen et al. (J Med Chem, 1998) describe a series of highly potent growth hormone-releasing peptides derived from ipamorelin, which is the structure-activity work underlying the compound.

Johansen et al. published twice in 1998 and 1999: a pharmacokinetic evaluation in Xenobiotica with emphasis on nasal absorption, and a report in Growth Hormone and IGF Research that ipamorelin induces longitudinal bone growth in rats. The bone growth result is the clearest in vivo demonstration of a downstream physiological effect.

These four papers from 1998 and 1999 carry most of the primary evidence. Very little primary work on this compound has been published since.

Recent context

Lu et al. (Physiol Behav, 2024) compare anamorelin and ipamorelin as GHS-R1a agonists in cisplatin-induced weight loss in ferrets, reporting that both inhibit weight loss while anamorelin also shows anti-emetic effects centrally. This is the most substantial recent primary work.

Five reviews published in 2026 place ipamorelin among therapeutic peptides in orthopaedics, sports medicine, aesthetics and gerontology. These reviews reflect current interest but add no primary data, and a reader tracing claims back through them will arrive at the 1998 and 1999 papers.