Several medications have received empirical support for the treatment of PMDD. Selective serotonin reuptake inhibitors (SSRIs) are the first-line medication. The U.S. Food and Drug Administration (FDA) has approved four SSRIs for the treatment of PMDD: Fluoxetine (available as generic or as Prozac or Sarafem), sertraline (Zoloft), paroxetine (Paxil), and escitalopram oxalate (Lexapro). Unlike treatments for depressive disorders, SSRIs do not need to be taken daily but instead can be taken only in the luteal phase or during PMDD symptoms. This is because those who respond to SSRIs usually experience symptoms relief within 1–2 days. Studies in rats suggest this rapid response to SSRIs is due to the elevation of the neuroactive progesterone metabolite allopregnanolone in the brain, rather than serotonin. Luteal phase dosing can be started 14 days before menses and subsequently discontinued after start of menstrual flow. Women taking SSRIs to ease PMDD generally report >50% alleviation in symptoms, which was significant improvement compared to placebo.