Testosterone is the male sex hormone, and it is important for people who are looking to build muscle, recover quickly between workouts if they are a performance athlete, and who generally want to feel strong and energetic. It is an important hormone for energy levels, and for the libido too. Both men and women produce some testosterone - men produce more, because they don't just produce it in the adrenal glands, they produce it in the testes too. Women produce only small amounts, because they only get it from the adrenal glands.