Long term use of Anabolic Steroids and androgens will reduce the number of sperm produced and affect their motility (swimming). This is why men on testosterone replacement therapy (gel, patches & injections) often have a low sperm count and infertility. Stopping these treatments will often lead to a higher sperm level and a return to normal fertility levels. Other drugs, such as Proviron, are weak androgen drugs and are known to have the same effect on generally lowering fertility levels for men. Sadly they are sometimes prescribed with the opposite intentions, to boost fertility, when doctors or pharmacists are out-of-date with international medical best practice.