When a female takes testosterone, the profound and permanent effects of the hormone can be seen in a matter of months. Voices drop, beards sprout, body fat is redistributed. Sexual interest explodes, aggression increases, and mood can be unpredictable. Our patients were told about some side effects, including sterility. But after working at the center, I came to believe that teenagers are simply not capable of fully grasping what it means to make the decision to become infertile while still a minor.