Tesamorelin

Overview

Tesamorelin is a synthetic analog of human growth hormone-releasing hormone (GHRH) developed by Theratechnologies Inc. of Montreal, Canada. It is the first and, as of 2026, the only GHRH analog to receive FDA approval, marketed under the brand names Egrifta and Egrifta SV for the reduction of excess visceral abdominal fat in HIV-infected patients with lipodystrophy.

HIV-associated lipodystrophy is a metabolic complication characterized by abnormal fat redistribution, including accumulation of visceral adipose tissue (VAT), often in the trunk and dorsocervical region. This condition is associated with antiretroviral therapy and contributes to cardiovascular risk, insulin resistance, and reduced quality of life. Tesamorelin was approved by the FDA in November 2010 following demonstration of significant VAT reduction in pivotal clinical trials.

Structurally, tesamorelin is the full 44-amino-acid sequence of human GHRH(1-44) with a trans-3-hexenoic acid modification at the N-terminus. This modification confers improved metabolic stability while preserving full agonist activity at the GHRH receptor (GHRHR) on anterior pituitary somatotroph cells.

Unlike exogenous growth hormone (GH) administration, which bypasses the hypothalamic-pituitary axis and can cause sustained supraphysiological GH and IGF-1 levels, tesamorelin stimulates endogenous GH secretion in a pulsatile, physiological manner. This mechanism preserves negative feedback regulation and is associated with a more favorable safety profile regarding glucose metabolism and other GH-related adverse effects.

Structure and Sequence

Tesamorelin consists of the full native human GHRH(1-44)-NH₂ sequence with a single N-terminal modification:

Sequence: trans-3-hexenoic acid-Tyr-Ala-Asp-Ala-Ile-Phe-Thr-Asn-Ser-Tyr-Arg-Lys-Val-Leu-Gly-Gln-Leu-Ser-Ala-Arg-Lys-Leu-Leu-Gln-Asp-Ile-Met-Ser-Arg-Gln-Gln-Gly-Glu-Ser-Asn-Gln-Glu-Arg-Gly-Ala-Arg-Ala-Arg-Leu-NH₂

• Molecular formula: C₂₂₁H₃₆₆N₇₂O₆₇S₁
• Molecular weight: approximately 5,135.9 g/mol
• CAS Number: 218949-48-5
• Key modification: Trans-3-hexenoic acid group attached to the N-terminal tyrosine, providing resistance to aminopeptidase degradation

The C-terminal amidation is present as in native GHRH(1-44)-NH₂. The compound is supplied as a lyophilized powder for reconstitution and subcutaneous injection.

Mechanism of Action

GHRH Receptor Activation

Tesamorelin binds to and activates the GHRH receptor (GHRHR), a class B G-protein coupled receptor expressed primarily on somatotroph cells of the anterior pituitary gland. Receptor activation triggers:

1. Gαs-coupled signaling — stimulation of adenylyl cyclase, increasing intracellular cAMP
2. PKA activation — protein kinase A-mediated phosphorylation cascades
3. GH gene transcription — increased expression of the GH1 gene
4. GH secretion — exocytotic release of stored GH from secretory granules

The resulting GH secretion occurs in a pulsatile pattern that mimics normal physiology, as opposed to the continuous elevation produced by exogenous GH injection.

Downstream Effects of Endogenous GH Release

The GH released in response to tesamorelin acts through:

• Direct lipolytic effects — GH stimulates hormone-sensitive lipase in adipose tissue, particularly visceral fat
• IGF-1 generation — hepatic production of insulin-like growth factor-1, which mediates many of GH's anabolic effects
• Metabolic modulation — improved lipid profiles, potential effects on insulin sensitivity

Preferential Visceral Fat Reduction

Tesamorelin demonstrates a preferential effect on visceral adipose tissue over subcutaneous fat. This selectivity is thought to relate to the higher density of GH receptors and greater lipolytic responsiveness of visceral adipocytes compared to subcutaneous adipocytes. The clinical significance is substantial, as visceral fat is more strongly associated with metabolic and cardiovascular risk than subcutaneous fat.

Research Summary

Pharmacokinetics

• Administration: Subcutaneous injection (abdomen)
• Bioavailability: approximately 4% (typical of peptide subcutaneous delivery)
• Tmax: approximately 0.15 hours (peak GH response occurs later, at approximately 0.5-1 hour)
• Half-life: approximately 26-38 minutes (tesamorelin itself); GH pulsatile release extends functional duration
• Dosing: 2 mg once daily (subcutaneous, abdominal injection)
• Steady-state GH/IGF-1: IGF-1 levels rise and stabilize within 2-4 weeks of daily administration
• Metabolism: Proteolytic degradation; the N-terminal modification slows but does not prevent enzymatic cleavage
• Clearance: Primarily renal and hepatic proteolysis

Tesamorelin's short plasma half-life is deceptive in terms of clinical effect — the compound triggers a downstream GH pulse and IGF-1 generation that extends the functional duration far beyond the peptide's own presence in circulation.

Dosing Protocols

Tesamorelin is FDA-approved as Egrifta for HIV-associated lipodystrophy.

FDA-Approved Protocol

• Dose: 2 mg (2,000 mcg) subcutaneous injection, once daily
• Timing: Before bed or morning on empty stomach
• Injection site: Abdomen (rotate sites)
• Cycle: Continuous use; clinical trials ran 26–52 weeks

Reconstitution (10 mg vial)

• Add 5.0 mL bacteriostatic water → 2.0 mg/mL concentration
• 2 mg dose = 1.0 mL per injection
• One 10 mg vial = 5 daily doses

Common Discussion Topics

Comparison to Exogenous Growth Hormone

Tesamorelin is frequently compared to direct GH administration (somatropin). Key distinctions include:

• Tesamorelin preserves pulsatile, physiological GH secretion with intact negative feedback
• Exogenous GH produces continuous supraphysiological levels that suppress endogenous production
• Tesamorelin has demonstrated a more favorable glucose metabolism profile
• Exogenous GH typically produces more dramatic effects on lean mass and strength
• Tesamorelin is FDA-approved only for HIV lipodystrophy, while somatropin has multiple approved indications

Cognitive Enhancement Research

Research from Massachusetts General Hospital has demonstrated improved cognitive function in HIV-positive patients treated with tesamorelin, particularly in executive function and verbal memory. The STAY-FIT trial is evaluating tesamorelin in age-related cognitive decline in HIV-negative populations. These findings have generated significant interest in tesamorelin as a potential cognitive compound, though the evidence base remains limited.

Discontinuation and Fat Reaccumulation

Clinical trials have consistently shown that visceral fat reduction achieved with tesamorelin reverses upon treatment discontinuation. VAT begins to reaccumulate within weeks of stopping the drug, returning to baseline levels over several months. This has implications for treatment duration and cost-benefit analyses.

Off-Label Interest

Despite its narrow FDA-approved indication, tesamorelin has attracted off-label interest for general anti-aging applications, body composition optimization, and cognitive enhancement. The compound's mechanism of stimulating endogenous GH production in a physiological manner is appealing compared to exogenous GH. However, data outside the HIV lipodystrophy population remains limited.

Related Compounds

• Mod GRF 1-29 — A modified GHRH fragment (CJC-1295 without DAC) that acts on the same GHRH receptor but with different pharmacokinetics
• Semaglutide — A GLP-1 agonist for weight management, sometimes compared in discussions about visceral fat reduction
• Tirzepatide — A dual incretin agonist for weight management and metabolic disease