Testosterone

Testosterone is the most important male sex hormone, predominantly produced in the testes and in smaller amounts in the ovaries and adrenal glands. It promotes the development of male sexual characteristics, muscle and bone growth, as well as the formation of red blood cells. In women, testosterone also plays a role in energy, mood, and libido.

Too low levels can lead to fatigue, lack of drive, reduced libido, and muscle loss in men. Too high levels are less common but can occur with hormone-producing tumors or through the intake of steroids.