As with any medication, a patient may experience an allergic reaction to the drug. These situations can be dangerous and will require immediate medical attention. The symptoms of an allergic reaction are hives, facial swelling, or trouble breathing. Other side effects that should be reported to a doctor include severe abdominal pain, constipation, a decrease in urination, hot skin, extreme thirst, and a burning or painful sensation during urination. Other, less serious adverse reactions include the following symptoms: dry mouth, diarrhea, nausea, dry eyes, impaired vision, dizziness, headaches, insomnia, runny nose, or general weakness.