Myrbetriq (mirabegron) is used to treat overactive bladder. Myrbetriq is a beta agonist, which works by relaxing blood vessels. The most common form of Myrbetriq is a 50mg tablet. It is also available as a bottle of oral solution. It is covered by some Medicare and insurance plans, but some pharmacy coupons, manufacturer programs, or cash prices may be lower. With the Patient Assistance Program from Astellas, you can receive your medication free of charge for up to one year.