But I'm not more aggressive—a behavior change often tied to testosterone. That's not surprising to Robert Sapolsky, ., a neuroendocrinologist at Stanford University and a leading researcher on stress and behavior. "It's really not the case that testosterone 'causes' aggressive behavior," he says. "Instead, it makes the brain more sensitive to social cues that trigger aggression. And in support of that, a guy's testosterone level isn't a very good predictor of how likely he is to be aggressive."
If your levels are low, you may be prescribed testosterone replacement therapy. Most men with low testosterone rub a testosterone gel on their arms or shoulders, according to the Urology Care Foundation . Another method is to get a shot into a muscle, or you can wear a patch that slowly releases testosterone into your blood. There are also pellets that go under the skin. There are oral replacement therapies as well, but these are not recommended for testosterone replacement. Men with prostate cancer shouldn’t take testosterone because it can fuel cancer growth.