Tesamorelin vs Hexarelin.

Tesamorelin is a synthetic 44-amino-acid analog of human growth hormone-releasing hormone (GHRH/GRF 1-44), stabilized by a trans-3-hexenoic acid group attached to its N-terminus. It is one of the few research peptides in its class that holds full FDA approval, marketed as Egrifta (and the reformulated Egrifta SV / Egrifta WR) by Theratechnologies for a narrow, specific indication. Originally designated TH9507, it is a secretagogue rather than a hormone itself.

Hexarelin (examorelin) is a synthetic hexapeptide growth hormone secretagogue (GHS), structurally derived from the GHRP-6 family of growth hormone-releasing peptides. It is an investigational compound that was studied in the 1990s and 2000s as a potential agent for probing and stimulating growth hormone secretion and, separately, for direct effects on the heart. It is not an approved drug.

Tesamorelin binds the GHRH receptor on the anterior pituitary, stimulating the synthesis and pulsatile release of the body's own growth hormone (GH), which in turn raises hepatic and circulating insulin-like growth factor-1 (IGF-1). Because it works upstream by amplifying endogenous GH secretion, it largely preserves physiological feedback and pulsatility, unlike direct exogenous GH administration. The N-terminal hexenoyl modification confers resistance to degradation (including by dipeptidyl peptidase-IV) and extends its half-life relative to native GHRH. The downstream rise in GH/IGF-1 drives lipolysis, with a notable effect on visceral (intra-abdominal) adipose tissue.

Hexarelin acts as an agonist at the growth hormone secretagogue receptor type 1a (GHS-R1a), the same pituitary/hypothalamic receptor activated by the natural hormone ghrelin. Receptor binding engages Gq/11-phospholipase C signaling, mobilizing intracellular calcium in pituitary somatotrophs and triggering pulsatile growth hormone release; this pathway is distinct from and synergistic with GHRH, and also opposes somatostatin tone. Hexarelin additionally binds CD36, a scavenger receptor expressed in cardiac and vascular tissue, which is the proposed basis for GH-independent cardiovascular effects observed in animal models. Because it is a non-selective secretagogue, it also stimulates ACTH/cortisol and prolactin release to a greater degree than more selective agents.

Human evidence is unusually strong for one specific population: HIV patients with lipodystrophy. Two pivotal phase 3 randomized, placebo-controlled trials and their pooled analysis (Falutz et al., JAIDS 2010 and J Clin Endocrinol Metab 2010) showed roughly a 15-18% reduction in visceral adipose tissue over 26 weeks, with regain after discontinuation, supporting the FDA approval. Stanley et al. (JAMA 2014; PMID 25038357) and a randomized NAFLD trial (Stanley et al., Lancet HIV 2019; PMID 31611038) further demonstrated reductions in liver fat and a lower rate of fibrosis progression in HIV-associated fatty liver disease. Crucially, nearly all rigorous human data come from HIV-positive cohorts; use for general anti-aging, body recomposition, or NAFLD in HIV-negative people is extrapolation and has not been established in large controlled trials. Subcutaneous fat and total weight are largely unaffected, and effects reverse when treatment stops.

Human data exist but are limited to small, short-term, acute physiology studies rather than outcome trials. Acute intravenous hexarelin reliably raised serum growth hormone in healthy volunteers and was compared head-to-head with GH in a controlled human study (Imbimbo/Ghigo group, J Endocrinol Invest 1999, PMID 10342360). Separate small studies reported short-lasting increases in left ventricular ejection fraction and cardiac output in normal subjects, GH-deficient patients, and dilated-cardiomyopathy patients, effects that appeared GH-independent (Bisi/Broglio et al., Endocrine 2001, PMID 11322491). A chronic-administration study found that GH responses desensitized over weeks and characterized effects on the pituitary-adrenal axis and prolactin (Clin Endocrinol 1999, PMID 10341859). Most cardioprotection evidence (CD36-mediated ischemia/reperfusion protection, IL-1 signaling) is preclinical and rodent-based (e.g., Int Heart J 2017, PMID 28321024; review J Geriatr Cardiol 2014, PMID 25278975); none of this advanced to a successful human cardiac outcome trial, and clinical development was discontinued.

The most consistent documented concerns are glucose-related: because it raises GH/IGF-1, tesamorelin can worsen insulin sensitivity and glucose tolerance, and IGF-1 levels are monitored in clinical practice. Common adverse effects in trials included injection-site reactions, arthralgia, myalgia, peripheral edema, and paresthesia; hypersensitivity reactions have occurred. It is contraindicated in pregnancy and in people with active malignancy, since elevated IGF-1 is a theoretical tumor-growth concern, and in those with disrupted hypothalamic-pituitary axis (e.g., pituitary tumor/surgery, head irradiation). The NIH LiverTox database assigns it a low likelihood of causing clinically apparent liver injury. Long-term safety beyond the trial windows, and safety in non-HIV populations, remains poorly characterized.

Documented effects in human studies include hexarelin's lack of GH selectivity: it raises cortisol, ACTH, and prolactin alongside growth hormone, so it does not produce a clean GH signal. A well-described limitation is rapid tachyphylaxis/desensitization, with attenuated GH responses on repeated or continuous dosing demonstrated both in vitro (second-messenger level) and over weeks of human administration. Long-term safety in humans is essentially unknown because no large or extended trials were completed; chronic GHS-driven IGF-1 elevation raises theoretical concerns common to this class (fluid retention, insulin sensitivity changes, and the general caution that growth-promoting signaling could be undesirable in the setting of malignancy), but these are not established for hexarelin specifically. There is no established safety profile for non-clinical/self-administered use.

FDA-approved (2010, as Egrifta; reformulated as Egrifta SV in 2019 and the F8 formulation Egrifta WR in 2023) solely to reduce excess visceral abdominal fat in HIV-infected adults with lipodystrophy. All other uses are off-label, and it is a prescription drug, not a dietary supplement.

Hexarelin is investigational and has never received FDA or EMA marketing approval; its clinical development was discontinued. It is prohibited in sport at all times by WADA as a growth hormone secretagogue / GH-releasing peptide under category S2 of the Prohibited List, and it is generally sold only as a research-use-only chemical.