US authorities on Tuesday approved the first medication designed specifically to treat postpartum depression, an illness that affects about one in nine new American mothers.

The drug is called brexanolone, from a company called Sage Therapeutics, and one advantage is that it works quickly, in 2 days, whereas traditional antidepressants can take weeks or months to kick in. The drug's trade name is Zulresso. It has been approved by the Food and Drug Administration (FDA). But it needs to be administered intravenously in a hospital over the course of 60 hours because of the risk of fainting that was observed in some women during clinical tests.

"Postpartum depression is a serious condition that, when severe, can be life-threatening. Women may experience thoughts about harming themselves or harming their child," said Tiffany Farchione, acting director of the division of psychiatry products in the FDA's Center for Drug Evaluation and Research.

"This approval marks the first time a drug has been specifically approved to treat postpartum depression, providing an important new treatment option," she added.

The most common secondary effects include drowsiness and dryness of the mouth. Sage Therapeutics said the medication will be available in late June in the United States.

US media say the treatment will cost $34,000 a year for people without health insurance. Insurers get it at a discounted rate. The full rate is without the cost of the hospital stay for administering it. The Centers for Disease Control and Prevention say 11.5% of new mothers suffered from post partum depression in 2012.