The causes of erectile dysfunction may be physiological or psychological. Psychological impotence can often be helped by almost anything that the patient believes in; there is a very strong placebo effect. Erectile dysfunction is characterized by the inability to maintain an erection. Normal erections during sleep and in the early morning suggest a psychogenic cause, while loss of these erections may signify underlying disease, often cardiovascular in origin. Other factors leading to erectile dysfunction are diabetes mellitus (causing neuropathy) or hypogonadism (decreased testosterone levels due to disease affecting the testicles or the pituitary gland).