Hi, Both HCTZ and Chlorthalidone are thiazide diuretics that can potentially cause a side effect of cough, although it is not as common as with ACE inhibitors such as lisinopril. Your cough may be a result of the switch to Chlorthalidone, but it could also be related to the previous use of HCTZ. If the cough persists or becomes severe, it is recommended to consult with your healthcare provider to determine the underlying cause and if a medication adjustment is necessary. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Priyanka, General & Family Physician