Although a common symptom of andropause, low sex drive is one of the first things to disappear with testosterone replacement therapy. A normal sex drive is usually achieved within five weeks of treatment. Testosterone has a strong effect on the brain, which is responsible for sexual desire. It also causes the brain to release a product called nitric oxide, which increases blood flow to the penis and aids in the ability to achieve and maintain an erection. In addition to low testosterone levels, high estrogen levels can also decrease sex drive. Testosterone replacement therapy and estrogen management can quickly and safely remedy this situation in most hormone deficient men.