(HealthDay)—The drug Oxytrol has been approved by the U.S. Food and Drug Administration as the first over-the-counter treatment for women 18 and older with overactive bladder.

is characterized by symptoms including leakage, frequent urination and feeling the sudden and urgent need to urinate. The condition affects some 33 million Americans, mostly older women.

Oxytrol contains oxybutynin, among a class of drugs called anticholinergics that are designed to relax the . Oxytrol is a patch applied to the skin every four days, the FDA said in a news release.

The drug will remain available for adult men by prescription only, the agency said.

Side effects reported during clinical testing included skin irritation at the patch site, dry mouth and constipation.

Oxytrol for Women is marketed by Merck, based in Whitehouse Station, N.J.

More information: To learn more about overactive bladder, visit the U.S. Department of Health and Human Services.