Even when accounting for changes in growth hormone levels, these muscles still got bigger, meaning the drug works through other pathways too.

Rising IGF-1 levels helped explain some of the muscle growth from the drug, but not all of it—so other factors are also at work.

Even though the drug raised IGF-1, that didn’t predict whether muscles got less fatty—so fat reduction in muscle must be happening through a different pathway.

The muscle growth from this drug wasn’t because belly fat went down—it was more likely due to a rise in a growth-related hormone called IGF-1.

Tesamorelin increased rectus and psoas muscle size by 0.44 and 0.46 cm² in people with HIV and belly fat, but this effect was reduced when considering changes in a growth hormone-related factor.

Even after accounting for belly fat loss, tesamorelin still increased lean muscle in people with HIV and belly fat, suggesting other factors are involved.