# Tesamorelin: What the GHRH-Analogue Research Actually Measured > Tesamorelin is a 44-amino-acid GHRH(1-44) analogue. In HIV lipodystrophy it cut visceral fat 15.2% and raised IGF-1 81%. Plain-English digest of the trials, mechanism, and regulatory scope, cited. A stripped-back reading of the literature: the mechanism, the pivotal-trial numbers, the half-life, and the exact regulatory line — every quantitative claim cited to its study. ## The short version Tesamorelin is a lab-made copy of a natural signal called GHRH (the brain's own "make growth hormone" message), tweaked so the body breaks it down more slowly. Given as a daily injection, it nudges the pituitary gland to release the body's own growth hormone in normal bursts, which raises IGF-1 (a growth signal the liver makes when growth hormone rises) and burns off visceral fat (the deep belly fat packed around the organs). In the studies that matter — adults living with HIV who had abnormal belly-fat buildup — 2 mg a day cut visceral fat by 15.2% over 26 weeks [1]. It is FDA-approved for that one HIV use and nothing else. ## What is tesamorelin? Tesamorelin is a synthetic 44-amino-acid analogue of human growth hormone-releasing hormone, GHRH(1-44) [8]. It carries a trans-3-hexenoic acid group on its N-terminus (one end of the peptide chain). That modification blocks the enzyme DPP-IV (a protease that normally chops up native GHRH within minutes), so tesamorelin stays active in the bloodstream longer than the hormone it imitates [8]. Its free base has the formula C221H366N72O67S and a molecular weight near 5,135.9 Da; it is supplied clinically as the acetate salt. The compound was approved in the United States in 2010 (NDA 022505) to reduce excess abdominal fat in HIV-infected adults with antiretroviral-related lipodystrophy [5]. A 2013 review of the GHRH-growth-hormone-IGF-1 axis in HIV identifies it as the only FDA-approved agent for reducing excess abdominal fat in HIV-associated lipodystrophy [6]. Every other use — general or cosmetic fat loss, anti-aging, performance, non-HIV fatty liver — is off-label and investigational [14]. This site reads the published record on [how tesamorelin works](/), summarizes [what the research shows](/research), and marks the regulatory line precisely. ## Tesamorelin as a peptide: structure of the stabilized GHRH(1-44) analogue Tesamorelin is a peptide hormone analogue, not a steroid and not a GLP-1 receptor agonist. The molecule reproduces the full 44-amino-acid sequence of native GHRH(1-44) and adds a single trans-3-hexenoyl group at the N-terminus [8]. That group is the entire engineering trick: native GHRH is cleaved at its second amino-acid position by DPP-IV almost as fast as it appears, while the modified N-terminus resists that cleavage, extending the peptide's plasma activity [8]. The term tesamorelin peptide is precise — it is a 44-residue chain, roughly fifteen residues longer than the truncated GHRH(1-29) sequence used by sermorelin. That length difference, and the N-terminal stabilization, are the structural basis for [tesamorelin vs sermorelin](/vs-sermorelin) comparisons. As a peptide, it carries a CAS number of 218949-48-5 and the drug class "growth hormone-releasing hormone receptor agonist." ## What does tesamorelin do? Tesamorelin prompts the pituitary to release the body's own growth hormone in natural pulses, which raises IGF-1 and promotes breakdown of visceral fat [4]. The clearest demonstration is the pivotal 26-week trial: in 412 HIV patients with abdominal fat accumulation, 2 mg/day reduced visceral adipose tissue by 15.2% while placebo rose 5.0%, cut triglycerides by 50 mg/dL, and raised IGF-1 by 81.0% [1]. What it does not do is supply growth hormone directly. It amplifies the body's existing rhythm rather than flooding the system with exogenous hormone — a distinction that shapes its metabolic profile [4]. The effect is also selective: it preferentially reduced visceral fat, generally without significant change in subcutaneous fat or BMI [13]. The [doses studied in trials](/dosage) were all once-daily, and the [tesamorelin side effects](/side-effects) reported track the growth-hormone axis it activates. ## Tesamorelin mechanism of action Tesamorelin binds the growth hormone-releasing hormone receptor (GHRH-R, a Gs-coupled receptor on the surface of pituitary somatotroph cells), activating the cAMP/PKA cascade (an internal chemical-messenger relay) that drives synthesis and pulsatile secretion of endogenous growth hormone (GH) [4]. The released GH then signals the liver to produce IGF-1, and GH and IGF-1 together activate lipolysis (the breakdown of stored fat) preferentially in visceral adipose tissue [6]. The mechanism was confirmed directly in 13 healthy men: 2 mg/day for two weeks raised mean overnight GH by 0.5 ug/L and increased IGF-1 by 181 ug/L, while neither fasting glucose nor insulin-stimulated glucose uptake changed significantly [4]. Because the compound resists DPP-IV, it sustains this GHRH-receptor signaling longer than native GHRH would [8]. ## Is tesamorelin a steroid? No — it's a GHRH peptide Tesamorelin is not a steroid. Steroids are lipid molecules built on a four-ring carbon skeleton; tesamorelin is a 44-amino-acid peptide hormone analogue [8]. It is also not a GLP-1 receptor agonist — it belongs to a different drug class entirely and was studied for a different indication. It works through the growth-hormone axis: GHRH receptor, then pulsatile GH, then IGF-1, then visceral lipolysis [4][6]. The confusion is understandable because all three classes touch metabolism and fat, but the mechanism and the molecule are distinct. ## Is tesamorelin FDA approved? Yes — but narrowly. Tesamorelin was approved in the United States in 2010 (NDA 022505) only to reduce excess abdominal fat in HIV-infected adults with antiretroviral-related lipodystrophy [5]. The NIH LiverTox monograph records that approval and assigns the drug a likelihood score of E for liver injury (an unlikely cause), noting no attributable liver-injury cases in trials [5]. Every other application — general visceral-fat reduction, cosmetic weight loss, anti-aging, cognitive enhancement, non-HIV fatty liver — is off-label and falls outside the approved indication [14]. A 2013 axis review names it the only FDA-approved agent for HIV-associated abdominal fat [6]. ## Tesamorelin half-life and plasma clearance Plasma exposure is short. Population pharmacokinetic modeling estimated an apparent plasma clearance near 1,060 L/h with no clinically relevant demographic covariates, and a roughly 13% higher absorbed fraction by day 14 than day 1 [16]. Secondary sources (the FDA label and Mayo Clinic) describe a terminal half-life on the order of 26 to 38 minutes. The biological effect outlasts the molecule. Despite rapid plasma clearance, the downstream IGF-1 elevation tesamorelin triggers persists across the dosing interval — which is why a once-daily regimen was the one studied [16]. This split between a fast-clearing peptide and a sustained hormonal signal is the defining feature of its [half-life and clearance](/dosage). --- Tesamorelin read down to its numbers — one GHRH(1-44) analogue, the visceral-fat and IGF-1 figures left standing alone against the studies that measured them, and the approved-for-HIV-lipodystrophy line drawn exactly where the off-label field begins; an editorial reference plate, not a clinic, a vendor, or a prescription.