One low-dose pill a day can cut stroke risk in older adults — that's how useful chlorthalidone has proven in big trials. It's a thiazide-like diuretic doctors often choose for high blood pressure and fluid retention (edema). Compared with hydrochlorothiazide, chlorthalidone lasts longer and can control blood pressure for 24+ hours.
So who should consider it? People with hypertension, those with swelling from heart or kidney issues, and patients where a long-acting diuretic fits the plan. Your doctor will decide if chlorthalidone is right for you based on other meds, kidney function, and potassium levels.
Typical starting doses are 12.5 mg to 25 mg once daily. Some patients need 50 mg, but higher doses raise the risk of low potassium and other side effects. Take it in the morning to avoid waking up at night to urinate.
Before you start, get baseline blood tests: kidney function (creatinine or eGFR) and electrolytes (potassium, sodium). Recheck these about 1–2 weeks after starting or changing the dose. If you feel dizzy, very thirsty, or see muscle cramps, contact your provider — those can be signs your electrolytes are off or you’re dehydrated.
Avoid taking extra potassium without checking first. Some people need a potassium supplement, others do fine with a potassium-rich diet (bananas, oranges, spinach). If you already take an ACE inhibitor, ARB, or potassium-sparing drug, your doctor will watch potassium closely.
Expect some increased urination, especially early on. Common side effects include low potassium (weakness, cramps, irregular heartbeat), low sodium (confusion, fatigue), elevated blood sugar, and higher uric acid, which can trigger gout attacks. Sun sensitivity and dizziness when standing up quickly are also possible.
Watch drug interactions: NSAIDs (ibuprofen, naproxen) can reduce chlorthalidone’s effect and worsen kidney function. Lithium levels can rise when you start a diuretic — that needs close monitoring. Combining with other blood pressure meds can lower blood pressure more than expected, so be careful when doses change.
Pregnancy and breastfeeding: thiazide diuretics are not the preferred choice in pregnancy. If you’re pregnant, planning pregnancy, or breastfeeding, talk with your clinician about safer options.
Quick tips: take in the morning, get labs within two weeks of starting, stay hydrated but avoid salt-heavy packaged foods, and report muscle weakness or rapid heartbeat right away. Chlorthalidone works well for many people, but like any drug, it needs smart monitoring to be safe and effective.
