A solution?

Our older son has been plagued by frequent trips to the bathroom for about 6 months. The last time I took him to the doctor they gave him a clean bill of health and offered little insight. This time the doctor did some tests that also came back fine. He indicated that he believed the problem might be an overactive bladder and prescribed medicine. It is too soon to tell if it is working but I am hoping it does. The only thing that worries me is the possible side effects. Some of the minor side effects include constipation but that is easily corrected with a colon cleansing diet or laxative. I am more worried about him having one of the rarer side effects like hallucinations or something. Our son is not a child who openly tells you when he isn't feeling like himself and I am watching him like a hawk to make sure he is not reacting to this drug. It would be great if the answer was a simple as him taking a pill once a day for a while to get his bladder into a more normal voiding routine.