a hand-marked lab notebook — what the literature actually drew out
Tesamorelin is a stabilized GHRH analogue studied for visceral fat and, in one trial, cognition.
A chemist's-notebook digest of the GHRH(1-44) chemistry, the visceral-fat and IGF-1 trials, the single cognition study, and the regulatory line that scopes it all — every figure jotted to its source.
The short version
Tesamorelin is a lab-made copy of the brain's own "make growth hormone" signal — a 44-amino-acid version of GHRH (growth hormone-releasing hormone, the hypothalamic peptide that tells the pituitary to release growth hormone). A small fatty-acid tag on one end keeps the body from chewing it up too fast. It nudges the pituitary to release the body's own growth hormone in natural bursts, which raises IGF-1 (a growth signal the liver makes when growth hormone rises) and trims deep belly fat. It is FDA-approved for one thing only: reducing excess abdominal fat in people with HIV-associated lipodystrophy. Everything else is off-label, and the lab-grade material discussed here is for research, not for people to inject.
Tesamorelin as a Research Peptide: What the Compound Is
Tesamorelin is a synthetic 44-amino-acid analogue of human growth hormone-releasing hormone, GHRH(1-44), with a trans-3-hexenoic acid group bonded to its N-terminus [1]. That single modification is the whole trick: it blocks DPP-IV (dipeptidyl peptidase-IV, a protease that snips native GHRH apart within minutes), so the molecule survives long enough to act [1]. The free base carries the formula C221H366N72O67S at a molecular weight of about 5,135.9 Da; it is supplied as the acetate salt, CAS 218949-48-5.
As a research peptide, tesamorelin sits in an unusual spot. Most compounds catalogued on sites like this are unapproved and rodent-only. Tesamorelin is the opposite — it is FDA-approved (NDA 022505, 2010) and backed by two pivotal Phase 3 human trials [3][4]. But that approval is narrow, covering only HIV-associated lipodystrophy (a fat-redistribution complication of HIV and antiretroviral therapy), and the research-grade powder sold for bench work is not the finished, quality-controlled drug product. This site reads the published record — how tesamorelin works, the studied doses and half-life, and tesamorelin side effects — and marks where the data is solid and where it runs thin.
What the Studies Report Tesamorelin Does
Three effects recur across the trial record. First, visceral-fat reduction: in a 26-week Phase 3 trial of 412 HIV patients, tesamorelin 2 mg/day cut visceral adipose tissue (the deep fat packed around the organs) by 15.2% while placebo rose 5.0% [3]. Second, hepatic-fat reduction: a JAMA trial measured a net liver-fat drop of -2.9% alongside that visceral change [5]. Third, IGF-1 elevation: the same pivotal program raised IGF-1 by 81.0% [3], the pharmacodynamic fingerprint of growth-hormone-axis stimulation.
The selectivity matters. Tesamorelin reduces visceral fat rather than subcutaneous fat (the fat under the skin) or overall body weight. A 2026 meta-analysis pooling five randomized trials reported a visceral-fat reduction of -27.71 cm2 and a hepatic-fat-fraction drop of -4.28% [13]. Every one of these figures comes from the HIV-lipodystrophy evidence base; that is the population in which tesamorelin was studied and approved, and the visceral-fat research is read here with that scope kept in plain view.
Mechanism of Action: GHRH-R Agonism and the GH/IGF-1 Axis
Tesamorelin binds the GHRH receptor (GHRH-R) on pituitary somatotrophs — the cells that make growth hormone — and switches on the Gs/adenylyl-cyclase/cAMP/PKA cascade, the standard signaling chain a receptor of this type uses to tell a cell to act [2]. The pituitary responds by synthesizing and releasing the body's own growth hormone in its natural pulsatile (burst-like) rhythm. That growth hormone then drives the liver to make IGF-1, and growth hormone together with IGF-1 promotes lipolysis (the breakdown of stored fat) preferentially in visceral fat [2].
The distinction from injected growth hormone is the point. Tesamorelin is a secretagogue — it prompts the body to release its own hormone rather than supplying a hormone from outside — so it amplifies a natural rhythm instead of overriding it [9]. The trans-3-hexenoic acid tag is what makes this durable: by resisting DPP-IV, the molecule keeps signaling long enough to matter [1]. A fuller account, including the cognition trial findings, sits on the research page.
Tesamorelin Is a Peptide, Not a Steroid
Tesamorelin is a synthetic GHRH(1-44) peptide analogue — a chain of amino acids — not an anabolic steroid. Steroids are lipid molecules built on a four-ring carbon skeleton that act on intracellular hormone receptors; tesamorelin is a 44-residue peptide that works at a cell-surface receptor (GHRH-R) to trigger the body's own growth-hormone release [2]. The two compound classes share neither structure nor mechanism. Tesamorelin also does not supply growth hormone itself; it is a secretagogue that prompts endogenous, pulsatile secretion [9].
Is Tesamorelin FDA Approved?
Yes — but narrowly. Tesamorelin was approved by the FDA in 2010 (NDA 022505) solely to reduce excess abdominal fat in HIV-infected adults with antiretroviral-related lipodystrophy [6]. That is the entire approved indication. Every other use — general or cosmetic fat loss, anti-aging, growth-hormone optimization, athletic performance, non-HIV fatty-liver disease — is off-label and not FDA-approved. The compound is also prohibited in sport under the WADA Prohibited List, category S2 (peptide hormones, growth factors, and mimetics), in- and out-of-competition. The regulatory status is the first thing this notebook circles, because the scope is the easiest fact to get wrong.
Reviewing the Published Tesamorelin Research
This site is a literature digest, not a vendor and not a clinic. The tesamorelin record is unusually deep for a compound in this catalogue: two pivotal Phase 3 RCTs in HIV-associated lipodystrophy [3][4], a JAMA hepatic-fat trial [5], a healthy-men mechanistic study [7], a cognition trial in older adults [8], an imaging substudy [10], and a 2026 meta-analysis of five trials [13]. Each is summarized in plain English and tied back to its source. The strongest findings — visceral-fat reduction, IGF-1 elevation — are read on the research page; the safety signals are read on the side-effects page; and the full citations sit in the full reference list.