How a single trans-3-hexenoyl group turns native GHRH into a longer-lived analogue, what the phase 3 and liver-fat trials actually found, what preclinical work showed, and how to handle tesamorelin in the lab.
Tesamorelin is the full 44-residue sequence of human growth hormone-releasing hormone (GHRH) with one small addition: a trans-3-hexenoyl group attached to the N-terminal tyrosine [6]. Among the peptides studied in GH-axis research, it is unusual in one respect. Alongside its preclinical work it has a substantial human clinical literature, including two phase 3 trials, a pooled analysis and randomized trials on liver fat. It is the active ingredient of Egrifta, which the FDA approved in November 2010 [9] to reduce excess abdominal fat in patients with HIV-associated lipodystrophy [3]. The tesamorelin sold by Northbridge Research Labs is a research-grade material. It is not Egrifta, has not been evaluated by the FDA, and is not intended for human use.
This overview explains why the N-terminal modification matters, summarizes what the trials reported as trial findings, describes the preclinical record, and closes with practical notes for laboratory work.
Native GHRH is a 44-amino-acid amidated peptide [1]. Its weakness is the N-terminal Tyr-Ala pair. In a 1986 study, GHRH(1-44)-NH2 incubated with human plasma was cleaved to GHRH(3-44)-NH2 with a half-life of 17 minutes, and the product retained less than one-thousandth of the original biological activity. After intravenous administration to healthy volunteers, the intact peptide had a half-life of 6.8 minutes. The authors attributed this to a plasma dipeptidyl aminopeptidase [5], the enzyme now known as DPP-4.
Tesamorelin, developed as TH9507, addresses this weak point directly. The non-clinical pharmacology report describes it as hGRF(1-44)-NH2 minimally modified by a trans-3-hexenoyl moiety on Tyr1. The modification made the peptide resistant to DPP-4, slowed its in-vitro degradation in rat, dog and human plasma, and prolonged plasma elimination in vivo [6]. The peptide chain itself is unchanged, so receptor recognition relies on the same 44 residues as the native hormone.
The design differs from approaches that extend exposure much further. Albumin-binding GHRH analogues such as CJC-1295 with DAC circulate for days. Tesamorelin remains a short-lived peptide: in dogs its apparent elimination half-life was 21 to 45 minutes [6]. That difference matters for anyone studying GH pulsatility, discussed below.
Tesamorelin acts at the GHRH receptor on pituitary somatotrophs. It stimulates the synthesis and release of the body's own GH rather than supplying GH directly [3]. GH in turn drives hepatic IGF-1 production. Because the peptide acts upstream, somatostatin tone and IGF-1 feedback stay in the loop.
The clearest human data on what this means for GH secretion come from a two-week study in 13 healthy men. Tesamorelin increased mean overnight GH, GH pulse area and basal GH secretion, and IGF-1 rose by 181 μg/L. Insulin-stimulated glucose uptake, measured by euglycemic clamp, did not change significantly [2]. For researchers, the result is that tesamorelin amplifies pulsatile secretion rather than replacing it with a flat, continuous signal.
The product page summarizes this literature briefly. The findings below are reported as results of the named trials, in the specific populations studied, using the pharmaceutical product under trial conditions.
The first phase 3 trial randomized 412 people with HIV and abdominal fat accumulation to tesamorelin or placebo for 26 weeks, with visceral adipose tissue (VAT) measured by CT as the primary endpoint. VAT decreased by 15.2% with tesamorelin and increased by 5.0% with placebo. Triglycerides fell by 50 mg/dL versus a 9 mg/dL rise, and IGF-1 increased by 81.0% versus a 5.0% decrease. Glycemic measures did not differ significantly between groups. Adverse event rates were similar, but more participants in the tesamorelin group withdrew because of an adverse event [1].
In the 26-week extension of that trial, the VAT reduction was sustained at 18% over 52 weeks in participants who continued on tesamorelin. In those switched to placebo, VAT reaccumulated [7]. A pooled analysis of both phase 3 trials covered 806 participants. At week 26 it reported a placebo-adjusted VAT difference of -15.4%, with no significant change in abdominal subcutaneous fat (placebo-adjusted difference -0.6%) and a mean IGF-1 increase of 108 ng/mL versus a 7 ng/mL decrease on placebo [8]. A review of the program reported serious adverse events in fewer than 4% of participants over 26 weeks, and noted that most events were local site reactions or effects known to accompany GH therapy, such as arthralgia, headache and peripheral oedema [3].
Two later trials looked at the liver. In a 6-month randomized trial of 50 people with HIV and abdominal fat accumulation, tesamorelin reduced VAT (placebo-adjusted difference -42 cm²) and liver fat (net -2.9% in lipid-to-water ratio). Fasting glucose rose at 2 weeks, but the difference was not significant at 6 months [4]. A 12-month multicentre trial then enrolled 61 people with HIV and non-alcoholic fatty liver disease. It reported an absolute reduction in hepatic fat fraction of 4.1 percentage points relative to placebo, a 37% relative reduction from baseline. At 12 months, 35% of the tesamorelin group and 4% of the placebo group had a hepatic fat fraction below 5% [11].
A 12-month randomized trial in 60 people with abdominal obesity and reduced GH secretion reported a placebo-adjusted VAT difference of -35 cm². Triglycerides, C-reactive protein and carotid intima-media thickness also improved. Abdominal subcutaneous fat did not change significantly, and fasting glucose, 2-hour glucose and HbA1c were unchanged [10].
Across these trials, one pattern keeps appearing: visceral fat falls while subcutaneous fat is largely preserved, alongside a clear rise in IGF-1. For a laboratory scientist, that depot selectivity is the most interesting open question, and the trials describe it without explaining it. These are findings about a licensed medicine in defined patient groups. They do not describe the effects of any other material, and they are not guidance for any use of a research compound.
The non-clinical program is described in a single 2007 paper. Plasma GH and IGF-1 rose markedly in pigs, rats and dogs given repeated tesamorelin. In subchronic toxicity studies lasting up to 4 months in rats and dogs, body weight gain increased, although the increase did not scale with the amount given. Dogs showed a more pronounced anabolic effect and more evident adverse findings, including liver and kidney changes, anaemia and organ-weight effects. These findings were reversible, and the authors attributed them to prolonged exposure to supraphysiological GH and IGF-1 [6]. The paper is a useful reference for species differences in response and for the endpoints worth monitoring in animal studies.
Northbridge Research Labs sends every batch for independent third-party testing. The certificate of analysis for tesamorelin lot TSM10001 (10 mg, tested August 2026) reports 99.47% purity and is published on our COA page.
Note: Tesamorelin from Northbridge Research Labs is supplied for laboratory research use only. It is not Egrifta or any other approved medicine, and it is not for human or veterinary use. Clinical trial results above are reported as published findings about the pharmaceutical product and are not guidance for any use.
Studied compound
Tesamorelin
The same material this research covers — 99%+ purity, independently tested, with the certificate for each batch published online.
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Research Use Only: The information in this article is for educational and research purposes only. All products mentioned are intended for laboratory research use only and are not approved for human or veterinary use.