The definition for impotence varies slightly among professionals, but it is generally considered to be the inability to achieve and maintain an erection sufficient for intercourse. A woman or man considering whether her or his boyfriend is impotent may be reluctant to initiate discussion about the issue.

Testosterone cypionate is an injectable steroid medication that is used as a hormone replacement therapy for males who do not make enough testosterone themselves. The controlled substance drug is sometimes also used by weight lifters to increase their strength, but it is not FDA-approved for this use.

Erectile dysfunction, or impotence, is a common disorder in men that has several causes. Vascular disease, which is dysfunction of the blood vessels as in atherosclerosis, is one common cause. Another potential cause is the side effects of particular medications.

Three types of medications to treat erectile dysfunction -- sildenafil, vardenafil and tadalafil -- may cause low blood pressure. Niacin, used to treat conditions such as high cholesterol and hardening of the arteries, can also lower your blood pressure.

If you're basically healthy, get regular erections in your sleep and have normal lab results, chances are that your erectile dysfunction is due to psychological factors, such as performance anxiety, relationship issues or a mood disorder.