Tesamorelin (TH9507) Peptide vs Ipamorelin

Tesamorelin and Ipamorelin both stimulate growth hormone release but act on fundamentally different receptor systems, making them mechanistically complementary rather than interchangeable. Tesamorelin (TH9507) is a synthetic analogue of endogenous growth hormone releasing hormone (GHRH) and acts directly on the GHRH receptor (GHRHR) — the same pathway as naturally occurring GHRH. It is the only GHRH analogue with clinical approval, having been authorised by the FDA as Egrifta for the reduction of excess abdominal fat in HIV-infected patients with lipodystrophy, giving it an unusually strong human evidence base for a research peptide. Ipamorelin, by contrast, is a selective growth hormone releasing peptide (GHRP) — a pentapeptide that activates the ghrelin receptor (GHSR-1a). Because it targets a different receptor to Tesamorelin, simultaneous activation of both pathways produces additive GH release, and preclinical studies frequently combine the two to maximise GH pulse amplitude while preserving selectivity. Ipamorelin is particularly noted in the research literature for its selectivity: unlike earlier GHRPs such as GHRP-6 and GHRP-2, it does not significantly elevate cortisol or prolactin, which has made it a preferred tool for studies where GH-specificity is important.