Tesamorelin is a synthetic version of growth hormone-releasing hormone, or GHRH. Researchers study it for how it nudges the pituitary to release growth hormone in a natural rhythm, with a special focus on visceral fat and metabolism.
What Tesamorelin Is
Tesamorelin is a 44-amino-acid peptide. It mirrors the body's own GHRH but adds a chemical tag, a trans-3-hexenoic acid group, to its N-terminus. That small change blocks DPP-4, an enzyme that normally chews up GHRH within minutes.
The peptide has a molecular weight of about 5,136 g/mol. It is sometimes called TH9507 in older papers and is marketed under the brand Egrifta in clinical settings. The U.S. Food and Drug Administration approved it for visceral fat reduction in HIV-associated lipodystrophy, a condition where fat redistributes around the abdominal organs.
How It Works
Tesamorelin binds GHRH receptors on somatotroph cells in the anterior pituitary. That binding triggers a cAMP and PKA signaling cascade, which tells the pituitary to make and release growth hormone, or GH.
The release pattern matters. Like sermorelin and other GHRH analogs, tesamorelin promotes pulsatile GH secretion. The body's natural feedback hormone, somatostatin, still works normally. That preserves the rhythm of high and low GH peaks that the body expects.
GH then travels to the liver and stimulates production of insulin-like growth factor 1, or IGF-1. IGF-1 and GH together drive lipolysis in visceral adipose tissue, the deep fat that wraps around organs. Dhillon (2011) reviewed this pharmacology and confirmed that tesamorelin works through GHRH receptor agonism rather than direct fat-cell action.
Key Clinical Findings
The pivotal Phase III trial set the foundation. Falutz and colleagues (2007) reported that tesamorelin reduced trunk fat by 15.2% and visceral adipose tissue by 18% over 26 weeks in patients with HIV-associated lipodystrophy. Subcutaneous fat changed less, suggesting a fairly selective effect on the deeper fat depot.
Researchers also explored cognitive effects. Stanley and colleagues (2015) studied cognitively normal older adults with elevated abdominal fat. The group on tesamorelin showed gains in executive function and verbal memory compared with placebo, hinting that the GH and IGF-1 axis may interact with brain aging.
These findings sparked further work in metabolic syndrome and nonalcoholic fatty liver disease. The visceral fat result is the most consistent across studies, but cognitive and liver-fat outcomes remain active research areas.
Why It Stands Out
Most GH-related compounds either give GH directly or stimulate GH receptors elsewhere. Tesamorelin sits one step earlier in the chain. By acting at the pituitary, it lets the body's own feedback loops set the ceiling on GH release.
That mechanism is appealing in research. It avoids the wide swings in GH that come with direct injection of the hormone itself. It also keeps somatostatin in the loop, which lowers the chance of runaway IGF-1 elevation in healthy tissue.
Researchers contrast tesamorelin with growth hormone secretagogues like ghrelin mimetics. The two pathways converge on GH release but use different receptors and different feedback signals. Studying both helps clarify how the GH axis behaves under different stimuli.
What Is Still Being Studied
Open questions include long-term effects on insulin sensitivity, durability of fat loss after the peptide is stopped, and whether the cognitive signals seen in older adults hold up in larger trials. Effects on liver fat and cardiovascular markers also need more data.
The mechanism is well mapped, but the broader metabolic story is still being written. These compounds are sold strictly for in vitro laboratory research and are not approved for human consumption.