Androgen replacement therapy (ART), often referred to as testosterone replacement therapy (TRT), is a class of hormone replacement therapy in which androgens, often testosterone, are replaced. ART is often prescribed to counter the effects of male hypogonadism. It typically involves the administration of testosterone, either by injection or by use of testosterone skin creams or gels. ART may also be prescribed to lessen the effects or delay the onset of normal male aging. However, this is controversial and is the subject of ongoing clinical trials, assessing the benefits and harms of its use in otherwise healthy older men. As men enter middle age they may notice changes caused by a relative decline in testosterone: fewer erections, fatigue, thinning skin, declining muscle mass and strength, more body fat. This dissatisfaction with the changes of aging has led to the development of the idea of androgen replacement therapy. Androgen replacement therapy is also used for men who have lost testicular function to disease, cancer, or other causes. For men who have had prostate cancer or at elevated risk, androgen replacement therapy remains controversial because some studies have shown that it increases the risk for prostate cancer; others refute that risk. Nonetheless, as of September 2014, testosterone replacement therapy has been under review for appropriateness and safety by the Food and Drug Administration due to the "potential for adverse cardiovascular outcomes".