Tesamorelin

Tesamorelin developed from the discovery of human growth hormone–releasing hormone and later efforts to improve the natural hormone’s short biological stability. It retains the complete 44-amino-acid GHRH sequence and adds an N-terminal trans-3-hexenoyl group designed to reduce enzymatic degradation.¹ Initially known as TH9507, tesamorelin entered clinical research as a way to stimulate endogenous pituitary growth hormone rather than administer growth hormone directly. Studies examined its effects on growth hormone, IGF-1, body composition and visceral adipose tissue in adults with HIV-associated lipodystrophy.²–⁶ In 2010, tesamorelin became the active ingredient in an FDA-approved prescription drug for reducing excess abdominal fat in adults with HIV-associated lipodystrophy.¹ ³ This approval is specific: it does not make tesamorelin a general weight-loss medication, and it does not apply to research-grade material sold outside the regulated drug supply chain. Later studies expanded into hepatic fat and other metabolic outcomes. Tesamorelin is therefore unusual among research peptides because its history includes controlled human trials and an indication-specific regulatory approval.

Tesamorelin binds the GHRH receptor, a class B G-protein-coupled receptor on somatotroph cells in the anterior pituitary. Its full GHRH sequence preserves receptor activity, while the N-terminal trans-3-hexenoyl modification improves stability.⁷ Receptor activation stimulates the Gs–adenylyl cyclase pathway, increasing cyclic AMP and activating protein kinase A. These signals support growth hormone synthesis and calcium-dependent secretion from pituitary cells.⁷ ⁸ The released growth hormone then acts on peripheral tissues, particularly the liver, increasing IGF-1 and IGF-binding protein 3.⁹ ² Downstream growth hormone signaling affects lipid mobilization, glucose regulation, protein metabolism and tissue remodeling. Tesamorelin does not directly bind a visceral-fat receptor; changes in visceral adipose tissue occur downstream of pituitary GH-axis stimulation. Randomized trials in adults with HIV-associated lipodystrophy support that indication-specific effect, which should not automatically be generalized to other populations.² Tesamorelin therefore follows the pathway GHRH receptor → cAMP/PKA → endogenous growth hormone → IGF-1/IGFBP-3. Its mechanism depends on a responsive pituitary and differs from direct growth hormone replacement.