IF WE ASKED you what testosterone does, you’d undoubtedly mention things like building strength and muscle mass, improving sex drive—in short, all the attributes we’ve come to equate with masculinity, especially when we’re at our peak in our late teens and early 20s. So, not surprisingly, when you no longer feel like the man you were and start to ask why, low T is often the culprit.

What is testosterone?

Testosterone belongs to a class of male hormones known as androgens (aka, steroids). It is both androgenic (causing male physical characteristics) and anabolic (causing development and growth of muscle), the latter being far more interesting to the average guy trying to get jacked.

Produced primarily in the testes and the adrenal glands, testosterone is involved with a variety of important processes in the body. It helps control development of male sex organs and kicks into high gear during puberty, when secondary sexual characteristics develop. These include not just an increase in size of the penis and testicles, but also the sprouting of facial and body hair. In addition, it is typically accompanied by a growth spurt and the development of stronger, more visible musculature.

As men mature, testosterone plays a critical role in sex drive, production of red blood cells and sperm, fat distribution, and—drumroll, please—the maintenance and increasing development of muscle mass and strength.