Tesamorelin: What the Research on a Stabilised GHRH Analogue Actually Shows

Unlike most research peptides, tesamorelin has a full phase 3 programme behind it. Developed by Theratechnologies under the code TH9507, it was approved in the US as Egrifta in November 2010 (Traynor, 2010). That makes it well documented, and also easy to overstate, because the approval covers one narrow use.

Structure: native GHRH with a protective cap

Tesamorelin keeps the entire 44-amino-acid sequence of natural GHRH, an amidated hypothalamic peptide (YADAIFTNSYRKVLGQLSARKLLQDIMSRQQGESNQERGARARL-NH2), and adds a trans-3-hexenoyl group, a six-carbon acyl chain with a double bond at position 3, to the N-terminal tyrosine (Ferdinandi et al., 2007). The formula is C₂₂₁H₃₆₆N₇₂O₆₇S, molecular weight about 5,136 daltons (CAS 218949-48-5). Sermorelin, by contrast, is the unmodified 29-residue fragment, covered in our sermorelin overview.

The cap exists because native GHRH is fragile. A plasma dipeptidyl peptidase strips its first two residues, leaving GHRH(3-44), with under a thousandth of the original activity; in volunteers, intact GHRH had a half-life below seven minutes (Frohman et al., 1986). The hexenoyl group makes tesamorelin resistant to this DPP-4 cleavage, slowing its breakdown in rat, dog and human plasma in vitro (Ferdinandi et al., 2007). It remains short-lived, with an elimination half-life measured in minutes (FDA, 2019).

Mechanism: amplifying the GH/IGF-1 axis from upstream

Tesamorelin binds GHRH receptors on pituitary somatotrophs and stimulates the synthesis and pulsatile release of endogenous growth hormone (GH). GH acts on liver, muscle, bone and fat, partly directly and partly through IGF-1, and is both anabolic and lipolytic (FDA, 2019).

Because tesamorelin acts upstream rather than replacing GH, release stays pulsatile. In 13 healthy men, two weeks of tesamorelin increased overnight GH, pulse area and basal secretion and raised IGF-1, while clamp-measured insulin sensitivity did not change significantly (Stanley et al., 2011). The clinical rationale was that excess visceral fat, in HIV and in obesity, goes with reduced GH secretion (Stanley et al., 2011; Makimura et al., 2012).

The visceral fat trials behind the 2010 approval

Visceral fat accumulates in many people with HIV on antiretroviral therapy, a pattern associated with increased cardiovascular risk (Falutz et al., 2007). The phase 3 trials measured visceral adipose tissue (VAT) by CT scan:

• First phase 3 trial (412 people, 26 weeks): VAT fell 15.2% on tesamorelin and rose 5.0% on placebo; triglycerides fell and IGF-1 rose 81%. Glycaemic measures did not differ, but more tesamorelin recipients withdrew because of adverse events (Falutz et al., 2007).
• Confirmatory trial (404 people, 26 weeks): VAT fell 10.9% against 0.6% on placebo, with no change in limb or abdominal subcutaneous fat (Falutz et al., 2010a).
• Pooled analysis (806 people analysed): a placebo-adjusted VAT reduction of 15.4% at 26 weeks, and VAT about 17.5% below baseline in those continuing to 52 weeks (Falutz et al., 2010b).

The effect was not durable: when participants switched to placebo, VAT reaccumulated (Falutz et al., 2008).

The FDA approved Egrifta on 10 November 2010 for reducing excess abdominal fat in HIV-infected patients with lipodystrophy (Traynor, 2010). Health Canada followed in 2014. Ferrer's European application was withdrawn in 2012, when the EMA's scientific committee held the provisional view that it could not be approved (EMA, 2012). There is no UK marketing authorisation; the tesamorelin on our UK tesamorelin page is supplied as research material, not a licensed medicine.

Beyond HIV, a 12-month trial in 60 adults with abdominal obesity and reduced GH secretion found reductions in VAT, triglycerides, C-reactive protein and carotid intima-media thickness without worsening glucose (Makimura et al., 2012).

Liver fat: the NAFLD and MASLD research

In 2023, non-alcoholic fatty liver disease (NAFLD) was renamed metabolic dysfunction-associated steatotic liver disease (MASLD) (Rinella et al., 2023); the tesamorelin trials use the older term. Because visceral and liver fat tend to travel together, Steven Grinspoon's group at Massachusetts General Hospital tested both. In a six-month trial of 50 people with HIV, tesamorelin reduced VAT and, modestly, liver fat; the authors called the study preliminary (Stanley et al., 2014).

The follow-up trial enrolled 61 people with HIV and a hepatic fat fraction of at least 5%. Over 12 months, hepatic fat fraction fell 4.1 percentage points more on tesamorelin than on placebo, a 37% relative reduction, and 35% of the tesamorelin group ended below 5% against 4% on placebo (Stanley et al., 2019). On paired biopsies, a secondary endpoint, fibrosis progressed in 2 people (10.5%) on tesamorelin and 9 (37.5%) on placebo, but existing fibrosis did not improve and the NAFLD activity score did not change significantly. Glucose and HbA1c did not differ. Gene expression in the same biopsies showed increased oxidative phosphorylation and reduced inflammation and tissue repair pathways (Fourman et al., 2020).

Two caveats apply. Nearly all of this work comes from one group, and a 2020 paper from that group discloses that Massachusetts General Hospital has a royalty and licence agreement with Theratechnologies for tesamorelin (Fourman et al., 2020). And the peer-reviewed evidence is HIV-specific. A phase 2 trial in 51 adults with obesity and NAFLD, not selected for HIV (NCT03375788), finished in January 2025 and has posted summary results, but no peer-reviewed report had appeared at the time of writing. A NASH programme outside HIV, announced by Theratechnologies in 2020, still lacked a partner in its fiscal 2023 annual report, and no such trial is registered.

Cognition: one positive trial, then mixed results

GHRH, GH and IGF-1 act on the brain and decline with age. A University of Washington trial randomised 152 adults aged 55 to 87, 66 with mild cognitive impairment, to tesamorelin or placebo for 20 weeks (Baker et al., 2012). Tesamorelin had a favourable effect on cognition, similar in both groups and driven mainly by executive function. IGF-1 rose 117%, and adverse events, described as mild, were reported by 68% on tesamorelin against 36% on placebo. An imaging substudy of 30 participants found higher brain GABA levels, but these did not correlate with cognitive changes (Friedman et al., 2013).

Later trials have not confirmed the effect. An open-label phase 2 trial in 73 people with HIV and abdominal obesity found no significant difference in cognition versus standard care after six months (Ellis et al., 2025), and a 10-week pilot in 22 adults found no significant changes in its standard analyses (Stewart et al., 2026). One positive trial justifies further study; it does not establish an effect.

An honest evidence assessment

The human evidence is stronger than for most research peptides, but it is concentrated in one question.

The visceral fat effect is reproducible, but VAT on a scan is a surrogate marker. No trial has shown fewer heart attacks, strokes or deaths, and the US label states that long-term cardiovascular safety has not been established and that the drug is not indicated for weight loss (FDA, 2019). The EMA committee's 2012 concerns were similar: no demonstrated health benefit from the fat reduction, trial participants with more abdominal fat than typical European patients, and no long-term safety data (EMA, 2012).

On safety, the trials reported GH-related effects such as arthralgia, headache and peripheral oedema, plus injection-site reactions (Dhillon, 2011). Average glucose was stable, but the label reports HbA1c of 6.5% or more in 5% of tesamorelin recipients against 1% on placebo at 26 weeks, and anti-tesamorelin antibodies in about half of participants (FDA, 2019). Raised IGF-1 is both the expected effect and the main theoretical concern, which the EMA committee linked to possible cancer risk and worsening diabetic eye disease (EMA, 2012). Two manufacturer-sponsored post-marketing studies, of long-term safety and of diabetic retinopathy, are listed as terminated in 2018 with no results posted (NCT01579695, NCT01591902).

The bottom line

Tesamorelin's core finding, a selective reduction in visceral fat in HIV-associated abdominal fat accumulation that lasts only while treatment continues, has held up across two phase 3 trials and an FDA review. The liver data are promising but small, HIV-specific and largely from one group; the cognition data are hypothesis-generating. For laboratory work, it is a well-characterised tool for probing the GH/IGF-1 axis from upstream.

References

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