A number of research studies have linked testosterone with male sexuality (Leprout & Van Cauter, 2011; O’Conner et al., 2011; Shah & Montoya, 2007). This research indicates that testosterone generally has a greater effect on male sexual desire (libido) than on sexual functioning (Crenshaw, 1996). Thus a man with a low testosterone level might have little interest in sexual activity but nevertheless be fully capable of erection and orgasms.
One source of information about testosterone’s effect on male sexual function is studies of men who have undergone castration. This operation, called orchidectomy in medical language, involves removal of the testes, and it is sometimes performed as medical treatment for such diseases as genital tuberculosis and prostate cancer (Parker & Dearnaley, 2003; Wassersug & Johnson, 2007). Two European studies reported that surgically castrated men experience significantly reduced sexual interest and activity within the first year after undergoing this operation (Bremer, 1959; Heim, 1981). Other researchers have recorded incidences of continued sexual desire and functioning for as long as 30 years following castration, without supplementary testosterone treatment (Greenstein et al., 1995). However, even when sexual behavior persists following castration, the levels of sexual interest and activity generally diminish, often markedly (Bradford, 1998; Rosler & Witztum, 1998). That this reduction occurs so frequently indicates that testosterone is an important biological instigator of sexual desire.
A second line of research investigating links between hormones and male sexual functioning involves androgen-blocking drugs. A class of drugs known as antiandrogens has been used in Europe and America to treat sex offenders as well as certain medical conditions, such as prostate cancer (Kafka, 2009; Kelly, 2008). Antiandrogens drastically reduce the amount of testosterone circulating in the bloodstream. One of these drugs, medroxyprogesterone acetate (MPA; also known by its trade name, Depo-Provera), has received a great deal of media attention in the United States. A number of studies have found that MPA and other antiandrogens are often effective in reducing both sexual interest and sexual activity in human males (and females) (Kafka, 2009). However, altering testosterone levels is not a completely effective treatment for sex offenders, especially in cases where sexual assaults stem from nonsexual motives, such as anger or the wish to exert power and control over another person (Kelly, 2008).
A third source of evidence linking testosterone to sexual motivation in males is research on hypogonadism, a state of testosterone deficiency that results from certain diseases of the endocrine system. Hypogonadism is also associated with the aging process in some older men (Page et al., 2011). If this condition occurs before puberty, maturation of the primary and secondary sex characteristics is retarded, and the individual may never develop an active sexual interest. The results are more variable if testosterone deficiency occurs in adulthood. Extensive studies of hypogonadal men provide strong evidence that testosterone plays an important role in male sexual desire (Corona et al., 2011; Jones et al., 2011; Kaminetsky et al., 2011). For example, hypogonadal men who receive hormone treatments to replace testosterone often experience increased sexual interest and activity (Kaminetsky et al., 2011; Dandona & Dhindsa, 2011; Seftel, 2012).