Erectile dysfunction is defined as the inability to achieve and maintain penile erection sufficient to permit satisfactory sexual intercourse. Testosterone is necessary for normal sexual arousal and in men testosterone deficiency is associated with impotence. However, various medications and recreational drugs are also known to affect sexual arousal and sexual performance. Sexual dysfunction as a consequence of drug therapy has been reported with a range of drugs, notably antihypertensives, antipsychotics and antidepressants.

Sexual function, in men, may be divided into three categories reflecting the sexual response cycle. Drugs can affect one or more phases of this cycle:

Libido or sexual desire
Arousal or erection
Release or ejaculation

Male sexual function depends on the co-ordination of neurogenic, hormonal and psychological mechanisms and disruption of one or more of these may result in erectile dysfunction.

Ejaculation describes the expulsion of seminal fluid from the posterior urethra. Disorders of ejaculation comprise ejaculatory failure and retrograde ejaculation in which semen passes into the bladder.

Drugs responsible for erectile dysfunction: About 25% of cases of erectile dysfunction are believed to be drug-induced. The classes of drugs most frequently implicated are antihypertensives, antidepressants, antipsychotics and anti-epileptics.

Antihypertensives: The prevalence of both erectile dysfunction and ejaculatory disorders is significantly greater in untreated hypertensive men so caution is needed when assessing whether medication is likely to be the cause of such problems. More recent studies confirm that the rate of erectile dysfunction depends on a class of antihypertensive medicines, for instance, methyldopa

Psychotropic drugs: As sexual dysfunction is a common feature of psychiatric illness, particularly depression, it can be difficult to assess the relative contribution of the disease and drug therapy. Both antidepressants and antipsychotics have recognized adverse effects on sexual function in men.

Miscellaneous: Some common examples of drugs that induce impotency include, but are not limited to: anti-androgens, anticholinergics, anti-depressants, digoxin (digitalis preparation which helps the heart beat more forcefully. It is used to treat congestive heart failure or cardiac arrhythmia), phenytoin (an anticonvulsant drug used to treat epilepsy) etc.

One notable drug-induced condition is Priapism in which the penis is continually erect; usually painful and seldom with sexual arousal. There is prolonged penile erection which is usually unrelated to sexual stimulation. The problem occurs when the regulatory mechanisms which initiate and maintain penile flaccidity are disturbed and venous drainage from the corpora cavernosa is obstructed.

Erectile Dysfunction can lead to a sense of hopelessness and lower self-esteem. Of course, feelings of sexual insecurity can reinforce any performance anxiety a man experiences and create a vicious cycle of repeated failures and increasingly negative feelings. Although sexual dysfunction is not life threatening, it can, however, have a major impact on personal relationships, quality of life and the ability to conceive.