Hi.. Thanks for the query.. Yes, dry mouth and mouth sores are due to Myrbetriq that contains active ingredient Mirabegron and is used for overactive bladder. Dry mouth is a common side effect of this drug and can secondarily cause mouth sores.. So my suggestion to you is to consult your treating Physician or Urologist and get evaluated. After proper examination he can either reduce the dose of the drug or change the medicine. For relieving the symptoms you can start using mouth lubricants in the form of gels that can be instilled in mouth for lubrication and reducing dryness like Oralbase. Along with it you can also chew sugar free chewing gums as they help in stimulation of saliva flow. For mouth sores, although they will spontaneously get better as the dryness will reduce but for symptomatic relief you can apply Lidocaine gel to relieve pain and do warm saline gargles. Sucking ice will also provide relief.. Hope you feel better soon.. Regards.