Tesamorelin is a GHRH analogue peptide that selectively reduced visceral fat across the HIV-lipodystrophy trials.

The short version

Tesamorelin is a lab-made copy of a natural body signal called GHRH (the brain's own "make growth hormone" message), tweaked so it lasts longer in the blood. Instead of injecting growth hormone directly, it nudges your own pituitary gland to release more of its own GH in the natural rhythm. That GH then raises IGF-1 (a growth signal the liver makes when GH rises), and together they break down fat — especially the deep belly fat packed around the organs. In its main trials it cut that deep fat by about 15%. It is FDA-approved for one job only: reducing excess deep belly fat in people with HIV-related fat changes. Every other use is off-label.

What the tesamorelin literature has established

Tesamorelin is a synthetic 44-amino-acid analogue of human growth-hormone-releasing hormone — GHRH(1-44) — carrying a trans-3-hexenoyl group at its N-terminus that resists DPP-IV cleavage and extends its activity over native GHRH ^[1]. In the pivotal 26-week Phase 3 trial of 412 adults with HIV-associated abdominal fat accumulation, tesamorelin 2 mg/day reduced visceral adipose tissue (VAT — the deep fat around the abdominal organs) by 15.2%, while placebo rose 5.0%; triglycerides fell 50 mg/dL and IGF-1 (insulin-like growth factor-1, a liver-made growth signal) rose 81.0% ^[1].

The effect held. Over 52 weeks of continued dosing, VAT reduction was sustained at -18% versus baseline, and a 2026 meta-analysis of five randomized controlled trials pooled a VAT reduction of -27.71 cm2 alongside a -4.28% hepatic-fat-fraction drop and a +1.42 kg gain in lean mass, with no serious adverse events reported ^[2][12]. This is an unusually mature evidence base for a research peptide: extensively trialed, FDA-reviewed, and consistent across studies.

What the data does not show is just as clearly marked here. The pivotal efficacy trials were all run in HIV-positive adults on antiretroviral therapy; no large general-population fat-loss trial has been completed, and visceral fat reaccumulates within weeks of stopping ^[2]. The pages below walk the record in order — read tesamorelin and visceral fat for the flagship track, the mechanism of action for how it works, or the full reference list for every citation.

Tesamorelin the Peptide: Structure and the GHRH Analogue Class

Calling tesamorelin a "tesamorelin peptide" is precise, not loose: it is a true peptide hormone, a chain of 44 amino acids with a molecular weight of 5135.9 Da and the empirical formula C221H366N72O67S, supplied clinically as the acetate salt ^[1]. Its sequence mirrors full-length human GHRH(1-44), the hypothalamic peptide that tells the pituitary to make growth hormone.

The single structural difference from native GHRH is the engineering that matters. A trans-3-hexenoic-acid group conjugated to the N-terminus blocks dipeptidyl peptidase-IV (DPP-IV) — the enzyme that rapidly chews up natural GHRH — so tesamorelin survives long enough in plasma to drive a meaningful GH pulse ^[1][7]. That places it in the GHRH-analogue class: a molecule that amplifies the body's own growth-hormone rhythm rather than supplying growth hormone from outside. For the molecule-by-molecule contrast with the older truncated GHRH(1-29) fragment, see tesamorelin vs sermorelin.

Mechanism in Brief: GHRH-R, Pulsatile GH, and IGF-1

Tesamorelin binds the GHRH receptor (GHRH-R) on pituitary somatotroph cells — the GH-making cells — and activates the Gs/adenylyl-cyclase/cAMP/PKA cascade that drives synthesis and pulsatile release of endogenous growth hormone ^[1]. That GH then signals the liver to produce IGF-1, and the GH/IGF-1 pair activates hormone-sensitive lipase to break down fat preferentially in visceral depots ^[1].

The distinction from injected growth hormone is the whole point: tesamorelin works upstream, amplifying the body's own pulsatile GH rhythm rather than flooding the system with a constant external supply ^[1]. In healthy men, 2 mg/day for two weeks raised mean overnight GH by 0.5 ug/L and IGF-1 by 181 ug/L while leaving insulin sensitivity intact ^[4]. The full pathway, kinetics, and dose data live in the mechanism of action module.

Is Tesamorelin a Steroid or a Growth Hormone?

Tesamorelin is neither. It is not an anabolic steroid — those are synthetic derivatives of testosterone with an entirely different chemistry and mechanism. And it is not exogenous (externally supplied) growth hormone either. It is a peptide GHRH analogue: it stimulates the pituitary to release the body's own GH in its natural pulsatile bursts ^[1].

That upstream mechanism is why its metabolic profile differs from recombinant GH. Where injected GH delivers a continuous external dose, tesamorelin amplifies the existing rhythm and lets normal feedback loops still operate ^[4]. The practical signature in trials was selective visceral-fat reduction with insulin sensitivity preserved in healthy men ^[4].

FDA Approval Scope: HIV-Associated Lipodystrophy Only

Tesamorelin is FDA-approved — and the scope is narrow and worth stating precisely. It was approved in the United States in 2010 (NDA 022505) to reduce excess abdominal visceral fat in HIV-infected adults with lipodystrophy, a fat-redistribution complication of HIV and its therapy ^[5]. That is the only FDA-approved indication.

Every other use — general or cosmetic fat loss, anti-aging, growth-hormone optimization, performance, non-HIV fatty-liver disease — is off-label and investigational, not FDA-approved ^[5]. Research-grade tesamorelin supplied for laboratory work is not the approved finished drug product and carries no human-use approval. Tesamorelin is also prohibited in sport under WADA category S2. The FDA approval scope and the labeled contraindications are detailed on the about and FAQ pages.