What side effects may I notice from receiving Methenamine Mandelate?

Side effects that you should report to your doctor or health care professional as soon as possible:
-allergic reactions like skin rash, itching or hives, swelling of the face, lips, or tongue
-bladder pain, irritation
-dark urine
-lower back pain
-painful, frequent urination

Side effects that usually do not require medical attention (report to your doctor or health care professional if they continue or are bothersome):
-diarrhea
-loss of appetite
-mouth sores
-nausea
-stomach upset

This list may not describe all possible side effects for Methenamine Mandelate. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.