Early or premature ejaculation is a dysfunction, the premature expulsion of semen during intercourse. It occurs when there has been very little sexual stimulation or when the person cannot keep control to maintain vaginal penetration for the desired time. It is relatively common and the causes are usually psychological, rather than physical: such as stress, depression, lack of confidence with a sexual partner, nervousness, excessive excitement, etc. Physical causes may originate in a low amount of serotonin. In this case, drugs that regulate the production of this substance in the brain are used. But usually the treatment involves psychological therapy.