Chlorthalidone is a long‑acting diuretic used to lower blood pressure and reduce fluid build-up. It works by helping your kidneys remove salt and water, which lowers blood volume and eases stress on the heart. Because it lasts longer than many thiazide diuretics, a single daily dose often controls blood pressure all day.
Doctors commonly prescribe chlorthalidone for high blood pressure and for swelling from heart or kidney problems. Typical starting doses are 12.5 to 25 mg once daily, usually taken in the morning. Some patients may need 50 mg, but clinicians often avoid higher doses because side effects rise with dose. Take it at the same time each day, and skip evening doses to prevent nighttime urination.
The most common side effects include increased urination, dizziness, and low potassium or sodium levels. Low potassium can cause weakness, cramps, or irregular heartbeat. Chlorthalidone can also raise blood sugar and uric acid, which may worsen diabetes or gout. Serious reactions are rare but include severe dehydration, lightheadedness, fainting, and allergic skin reactions. Avoid using NSAIDs like ibuprofen often, because they can blunt the blood pressure effect. Tell your doctor if you take lithium, digoxin, ACE inhibitors, ARBs, or other blood pressure meds — doses may need adjustment. Also mention supplements like potassium or salt substitutes; these can dangerously raise potassium if used without supervision.
Take it in the morning with a glass of water. If you feel dizzy on standing, rise slowly and sit for a minute before walking. Get blood tests as your doctor asks — they will check electrolytes and kidney function within a few weeks of starting and periodically after that. Monitor your blood pressure at home and keep a log to share at appointments. Stay hydrated, especially in hot weather, but avoid large amounts of alcohol which can increase dizziness and dehydration. Limit or avoid high‑potassium salt substitutes unless your doctor says it’s okay.
Contact your provider if you have severe weakness, muscle cramps, fainting, very fast or irregular heartbeat, severe dizziness, confusion, or little to no urine. Also call if you get a rash, swelling, or trouble breathing.
Chlorthalidone is generally not recommended in pregnancy; discuss safer options with your clinician. If you breastfeed, mention this to your doctor so they can weigh risks and benefits.
Store chlorthalidone at room temperature away from moisture and heat. It may cause sensitivity to sun, so use sunscreen and protective clothing. If you plan travel, pack enough medication and keep a list of your prescriptions. Do not stop taking chlorthalidone suddenly without talking to your doctor — blood pressure can rebound. Ask about generic options to reduce cost. Stay informed.
If you have questions about how chlorthalidone fits your care, ask your prescriber or pharmacist. They can review your dose, other medicines, and the tests you need.
