AndroGel, Testim, Axiron, Fortesta and Natesto are all types of testosterone gels, according to WebMD. Testosterone gel can be applied directly to the skin, through a pump or nasally.
Doctors prescribe testosterone replacement therapy for men who have low testosterone and exhibit symptoms of low testosterone, explains WebMD. Testosterone replacement therapy is not recommended for men who have decreased testosterone levels due to aging. Testosterone supplements come in skin patches, gels, mouth patches, injections and implants. Testosterone pills are also available, but they may have negative side effects on the liver. The other forms of testosterone supplements deliver testosterone directly into the bloodstream, bypassing the liver.