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.

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.

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

In people with HIV and belly fat who responded to tesamorelin, muscle density changes were linked to belly fat loss but not to changes in a growth-related hormone.

Changes in a growth hormone-related factor didn't match changes in muscle density or size in people with HIV and belly fat taking tesamorelin.