Ipamorelin, the first selective growth hormone secretagogue — VialBase Research

Summary

This foundational study established ipamorelin as the first truly selective growth hormone secretagogue. Unlike other GH-releasing peptides (GHRP-6, GHRP-2, hexarelin), ipamorelin stimulates GH release without significantly affecting cortisol, ACTH, or prolactin levels, even at high doses.

Key Findings

• Ipamorelin releases GH with potency similar to GHRP-6
• Does NOT increase cortisol or ACTH secretion (unlike GHRP-6 and GHRP-2)
• Does NOT significantly increase prolactin levels
• Selectivity maintained even at doses 200x the effective GH-releasing dose
• GH release is dose-dependent and reproducible
• Acts through the ghrelin/GHS receptor (GHS-R1a) at the pituitary

Methodology

In-vivo studies in swine comparing ipamorelin with GHRP-6 and GHRH. Intravenous bolus dosing at multiple dose levels. GH, cortisol, ACTH, and prolactin measured via serial blood sampling. Selectivity assessed by comparing hormone profiles across dose ranges.

Limitations

• Animal study (swine) — selectivity needs confirmation in human dose-response studies
• Single-dose pharmacology — no chronic dosing data
• No body composition or functional outcomes assessed
• Ghrelin receptor agonism means potential appetite stimulation (not assessed)
• Commercial development for ipamorelin not pursued to regulatory approval

Relevance to Content

The defining paper for ipamorelin’s key selling point: selectivity. This is why ipamorelin is preferred over older GHRPs in peptide therapy — it releases GH without the cortisol spikes or prolactin elevation that other GH secretagogues cause. Essential citation for any content comparing GH secretagogues or explaining why ipamorelin is favored.

See Also

• Parent compound: Ipamorelin