Impotence may have a physical, lifestyle, or psychological cause. An underlying medical condition is the most common cause of impotence. Such conditions may interfere with the blood supply to the penis, the generation of nerve impulses involved in getting and maintaining an erection.

Some medical conditions that commonly cause impotence include diabetes, cardiovascular disease, atherosclerosis, or the hardening of the arteries, kidney disease, and diseases affecting the nervous system. Diabetes causes damage to both blood vessels and nerves. Cardiovascular and other vascular diseases reduce the flow of blood to the penis, and the veins that remove blood from the engorged penis may be leaky. Kidney disease may cause impotence through chemical changes that affect circulating hormones, blood supply, nerves and overall energy. Conditions that affect the brain or nerves, such as stroke, Alzheimers disease, or multiple sclerosis may all interfere with the flow of nerve impulses that are needed for an erection.

Besides medical conditions, surgery that involves the bladder or prostate and pelvic and spinal cord injuries may affect nerves supplying the penis or involved in maintaining an erection. Certain hormonal imbalances such as low testosterone levels can also cause impotence and several types of prescription drugs can cause impotence as a side effect.

Lifestyle factors implicated in impotence are lack of physical exercise, being overweight, and the use of alcohol, smoking and illegal drugs. Alcohol and tobacco cause damage to blood vessels and nerves. Lifestyle factors may exist alone or be accompanied by psychological factors such as depression.

Psychological causes of impotence include stress, anxiety, depression, or guilt. Sometimes, people who have been physically or sexually abused may suffer from psychological impotence. Another cause of psychological impotence is confusion about ones sexual identity. Often, someone with an underlying physical condition may also be depressed or anxious, adding to the combination of factors causing impotence.