Testosterone is an important male hormone. In men, it’s mostly produced in the testicles.
Testosterone is responsible for building muscles and bone mass and for stimulating sperm production. the testosterone levels also factor into the sex drive.
Normal testosterone levels will vary. However, adult men are considered to have low testosterone, or low T when their levels fall below 300 nanograms per deciliter (ng/dL).
When the testosterone levels decrease, the desire for sex also decreases.
Decreasing testosterone is a normal part of aging. However, a drastic drop in testosterone can lead to decreased libido.