Myrbetriq (mirabegron) is used to help with overactive bladder (OAB) in adults. It can also treat a bladder problem called neurogenic detrusor overactivity (NDO) in children 3 years and older. It works as a beta-3 adrenergic agonist to help the bladder hold more urine. Myrbetriq (mirabegron) is taken by mouth once a day. It comes as a brand-name or generic extended-release tablet. A solution made from granules of the medication is available for children, but it's brand name only. Side effects include high blood pressure, cold symptoms, and urinary tract infections.