Diuretics: How "water pills" work and what you must know
Diuretics, aka water pills, push excess salt and water out of your body. People use them for high blood pressure, swollen ankles, heart failure, certain kidney or liver problems and some kinds of glaucoma. They can be very helpful — but they also change your electrolytes, blood pressure and how you feel day-to-day.
How diuretics work
There are several types. Thiazide diuretics (like hydrochlorothiazide 12.5–25 mg) lower blood pressure and are common in long-term care. Loop diuretics (furosemide 20–40 mg) are stronger and used when fluid builds up fast. Potassium-sparing diuretics (spironolactone 25–50 mg) keep potassium from dropping but have their own side effects. Other types include carbonic anhydrase inhibitors (acetazolamide) and osmotic diuretics (mannitol) for specific conditions.
Each works in a different part of the kidney. Thiazides stop sodium reabsorption in a distal tubule, loops act on the loop of Henle, and potassium-sparing ones work at the collecting duct. That’s why doctors choose one over another depending on how much and how fast they want to remove fluid.
Practical safety tips
Start low and watch closely. Common side effects are dehydration, low potassium or sodium, dizziness when standing, higher blood sugar, and higher uric acid (which can trigger gout). Spironolactone can cause breast tenderness or hormonal changes in men and women. If you feel lightheaded, weak, or have muscle cramps, call your provider.
Take diuretics in the morning so you’re not up all night. If the dose is twice daily, take the second dose no later than early afternoon. Weigh yourself every morning and track swelling. A quick 2–3 lb gain overnight can signal fluid changes that need review.
Check labs. After starting or changing dose, get electrolytes and kidney function checked within 1–2 weeks. If you’re on drugs like ACE inhibitors, ARBs, NSAIDs, or lithium, tell your doctor—these interact and may raise the risk of kidney problems or abnormal potassium.
Pregnancy and breastfeeding need extra care. Some diuretics are not recommended. Don’t stop or start them without talking to your clinician. If you have diabetes, gout, or low blood pressure, mention that when treatment is planned.
Watch drug interactions. ACE inhibitors and ARBs can increase potassium, especially with potassium-sparing diuretics. NSAIDs like ibuprofen or naproxen may blunt diuretic benefit and harm kidney function. Lithium needs close monitoring because diuretics and dehydration can raise lithium levels. Always list every prescription, OTC drug and supplement to your prescriber.
Simple diet moves help. Cut added salt to reduce fluid buildup. If you're losing potassium, include bananas, spinach, beans — but check with your doctor before adding potassium supplements. Stay hydrated but avoid gulping water if your doctor told you to limit fluids. Carry a med list and weigh yourself daily during treatment changes.
Ask questions.
