People who are allergic to sulfa drugs should not take chlorthalidone. Sulfa drugs include medicines like the antibiotic Bactrim. People with a known allergy to sulfa drugs may have allergic reactions to chlorthalidone. Because of this, doctors usually recommend a different medicine.

If you have had an allergic reaction to chlorthalidone in the past, you should not take it again. People with other types of allergies can usually safely take chlorthalidone. Tell your doctor about all allergies, especially to medicines.

Telling your doctor is the key when you have an allergy!