the lack or loss of ability to achieve an erection. It may be primary, in which a man has never been able to achieve erection sufficient for sexual intercourse; or secondary, in which a man is no longer capable of producing or maintaining an erection or can have one only in some situations (e.g., during masturbation) or with some partners. Causes of erectile dysfunction may be psychological or physical, including the effects of medications or drug abuse. If a man normally experiences a nocturnal erection or is able to induce an erection by masturbation, but cannot achieve or maintain an erection during sexual intercourse, the dysfunction is assumed to be due largely or solely to psychological factors. See male erectile disorder.