Within days of giving birth, a woman’s estrogen and progesterone levels quickly drop, leading to chemical changes in the brain that might give rise to shifts in mood. In fact, as many as three in four mothers experience symptoms of depression soon after childbirth. But for one in nine mothers, those symptoms result in a more serious, longer-lasting, and potentially life-threatening condition known as postpartum depression. The disorder, which manifests as a significant change in mood within hours to weeks of giving birth, is the most common complication of pregnancy. Currently, the depression drugs used to treat it take weeks to months to kick in—time that new mothers (and their infants) can’t afford. Zulresso is the first FDA-approved medication designed to tackle postpartum depression, and it does so at speed. The drug is a synthetic form of allopregnanolone, a hormone that dampens neural activity and eases depression symptoms when estrogen and progesterone levels dip. In double-blind control studies run by the creators at Sage Therapeutics, Zulresso worked within 60 hours. Right now, the drug is administered via a 60-hour intravenous infusion (common among new medicines), but alternative treatments, including a pill form, are currently in clinical trials.