Tesamorelin is an analog of our body’s natural GHRH, so it binds to GHRH receptors on the pituitary gland in the brain. By doing so, it stimulates the pituitary to secrete growth hormone in a pulsatile manner. The key difference between Tesamorelin and some other GH secretagogues (like MK-677 or GHRP-6) is specificity: Tesamorelin acts upstream on the GHRH receptor and does not activate the ghrelin receptor. This means it increases GH release without raising ghrelin, so it doesn’t cause increased hunger or elevated prolactin/cortisol (side effects associated with ghrelin mimetics). The resulting boost in GH leads to a subsequent rise in IGF-1 levels (IGF-1 is produced by the liver in response to GH). Elevated IGF-1 is largely responsible for the visceral fat reduction effect: Tesamorelin was specifically developed to reduce abdominal fat in HIV patients with lipodystrophy, and it preferentially targets visceral adipose tissue, likely through IGF-1 mediated lipolysis. Studies found significant reductions in VAT (visceral adipose tissue) after several months of use. Additionally, GH/IGF-1 improves metabolism of lipids and carbohydrates, hence the observed improvements in cholesterol and triglyceride levels. In terms of pharmacokinetics, Tesamorelin triggers an acute surge of GH shortly after injection that tapers within a couple of hours, while IGF-1 remains elevated for a sustained period (over 20 hours). This pattern can be complementary with other GH secretagogues; for instance, some advanced users combine Tesamorelin (rapid spike) with MK-677 (long baseline) to maximize 24-hour GH levels. Overall, by specifically activating the GHRH pathway, Tesamorelin achieves a potent increase in growth hormone output with a safety profile that avoids many off-target effects.