Premenstrual dysphoric disorder (PMDD) can be considered a severe form of premenstrual syndrome (PMS). Both PMS and PMDD are characterized by unpleasant physical and psychological symptoms that occur in the second half of a woman's menstrual cycle, most commonly in the days preceding the menstrual period. Premenstrual dysphoric disorder (PMDD) can be considered to be a severe form of premenstrual syndrome (PMS), with symptoms that interfere with daily activities and functioning.