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Body journey · 7 steps

Inside the body with Tesamorelin

Tesamorelin is a lab-made copy of a natural brain hormone that tells the pituitary gland to release growth hormone. It is approved in the US for one narrow use: reducing extra belly fat in adults with HIV who have a fat-distribution problem called lipodystrophy. It is not approved for general weight loss.

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  1. 01Skin

    Injected under the skin

    The medicine is a short chain of amino acids that is injected just under the skin of the belly. From there it seeps into tiny blood vessels. Only a small share of it makes it into the blood.

    For experts +

    Given by subcutaneous injection, tesamorelin has an absolute bioavailability of under 4% in healthy adults (measured with the original formulation). Median Tmax is 0.15 h, and the mean volume of distribution after a single subcutaneous dose of Egrifta WR was 4.8 +/- 1.9 L/kg in healthy subjects. With the original formulation, AUC was 34% higher in HIV-infected patients without lipodystrophy than in healthy subjects, with similar Cmax.[src]

  2. 02Bloodstream

    Gone from the blood within minutes

    Once in the blood, the peptide does not last long. Half of it is gone in about 11 minutes. Even so, that short burst is enough to give the pituitary gland a nudge.

    For experts +

    Mean elimination half-life is 11 minutes after a single subcutaneous dose of Egrifta WR in healthy subjects (26 and 38 minutes in healthy subjects and HIV-infected patients respectively for the original formulation). No formal metabolism studies have been performed in humans. Pharmacokinetics in renal or hepatic impairment, children and elderly patients have not been established.[src][src]

  3. 03Brain

    Switches on the GHRH receptor in the pituitary

    At the base of the brain, the pituitary gland makes growth hormone. It has a docking site for a natural signal called GHRH. Tesamorelin is a copy of that signal, so it fits the same site and switches it on.

    For experts +

    In vitro, tesamorelin binds and stimulates human GHRH receptors with potency similar to endogenous GHRH. The receptor is a class B GPCR that couples to Gs. A cryo-EM structure of GHRH(1-44) bound to the human receptor and Gs (PDB 7CZ5) shows the natural ligand's binding mode; a tesamorelin complex was not found in the sources reviewed, so its pose is inferred from the natural hormone.[src][src]

  4. 04Brain

    Pituitary releases growth hormone

    When the docking site is switched on, the pituitary releases growth hormone into the blood. Levels of other pituitary hormones stayed about the same in the trials.

    For experts +

    GHRH acts on somatotrophs to stimulate synthesis and pulsatile release of endogenous GH. In trials tesamorelin raised GH secretion and thereby IGF-1 and IGFBP-3, with no clinically significant changes in TSH, LH, ACTH or prolactin (label clinical pharmacology). IGF-1 rose 81.0% versus a 5.0% fall on placebo in the first phase 3 trial. This is shown in humans.[src][src]

  5. 05Liver

    The liver makes more IGF-1

    Growth hormone tells the liver and other tissues to make a helper hormone called IGF-1. In the trials, IGF-1 went up a lot. Doctors check IGF-1 levels because nobody knows what long-term high levels do.

    For experts +

    Some, but not all, GH effects are mediated by IGF-1 produced in the liver and peripheral tissues. In the two 26-week phase 3 trials, mean IGF-1 rose by 107 and 108 ng/mL with tesamorelin (mean treatment differences versus placebo 122 and 105 ng/mL); 47% of tesamorelin-treated patients exceeded 2 SDS and 36% exceeded 3 SDS at 26 weeks. The label calls for IGF-1 monitoring, and the effects of prolonged elevation are unknown.[src][src]

  6. 06Fat tissue

    Belly fat around the organs shrinks

    Growth hormone helps the body break down fat, especially the deep fat packed around the organs in the belly. In trials with people who have HIV, that deep fat went down by about 15% compared with placebo. Fat just under the skin stayed about the same.

    For experts +

    GH is lipolytic, and tesamorelin selectively reduced visceral adipose tissue (VAT) on CT: a treatment effect of -15.4% at week 26 in the pooled phase 3 analysis (-24 vs +2 cm2), with no significant change in abdominal subcutaneous fat (-0.6%). The reduction was maintained to week 52 with continued treatment. Triglycerides and the total cholesterol to HDL ratio also improved. These effects are shown in HIV-infected adults with abdominal fat accumulation only.[src][src][src]

  7. 07Liver

    Possible effect on fat in the liver (unapproved, small trials)

    Two small studies in people with HIV found that tesamorelin also lowered fat stored in the liver. These studies are early, and using the medicine for liver fat is not approved anywhere we checked.

    For experts +

    In a 50-patient randomised trial, liver fat fell by a net 2.9 percentage points (lipid-to-water) over 6 months versus placebo (JAMA 2014). In a 61-patient randomised trial in people with HIV and NAFLD, hepatic fat fraction fell by an absolute 4.1% versus placebo at 12 months, and 35% versus 4% reached HFF below 5% (Lancet HIV 2019). These are small, exploratory human trials in HIV only; this indication is unapproved.[src][src]

Schematic animation — real structure where marked

Under the skin

Step 01 of 07

AI-generated illustration · not to scale

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What is real and what is drawn

The scenes are schematic animations made for this page. Shapes, colours, speeds and sizes are chosen to explain, not to measure. Nothing is to scale.

  • Related structure: Experimental structure · cryo-EM 2.6 Å · PDB 7CZ5 (2020). It shows GHRH(1-44) (native hormone), not Tesamorelin. From “Structural basis for activation of the growth hormone-releasing hormone receptor.” Nat Commun 2020. RCSB PDB entry. The coordinates are experimental; the movement into place is illustrative.

Transitions between scales use short clips labelled “AI-generated illustration”. They are generated images, not recordings or simulations.

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