List of products in the National Drug Code with proprietary name . This medication is used to treat overactive bladder. Overactive bladder is a problem with how your bladder stores urine that causes a sudden urge to urinate. The urge may be hard to control, and overactive bladder symptoms may include frequent urination, strong sudden urges to urinate, or involuntary loss of urine (incontinence). Mirabegron works by relaxing a certain bladder muscle (detrusor), which helps the bladder hold more urine and lessens symptoms of overactive bladder.