The FDA has approved Merck's (MRK 0.44%) Oxytrol for Women, the first over-the-counter treatment for overactive bladder in women, a condition that Merck says affects more than 20 million American women.

Overactive bladder is characterized by a strong urge to urinate right away and the need to urinate more often. It typically affects women between the ages of 45 and 60.

Oxytrol was previously a prescription-only patch, but Merck convinced the FDA that it was safe enough for over-the-counter status. The company ran a series of studies to prove that women could correctly diagnose that they have overactive bladder and that they could use the patch correctly unsupervised.

Merck licensed Oxytrol as an over-the-counter treatment for overactive bladder from Watson Pharmaceuticals, now known as Actavis. Oxytrol will remain as a prescription drug for the treatment of overactive bladder in men.

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