Furosemide: What it does, how to use it, and what to watch for

Furosemide is a loop diuretic often used to remove extra fluid from the body. You’ve probably heard it called "Lasix"—that’s the brand name. Doctors prescribe it for swelling from heart failure, liver disease, kidney problems, and sometimes high blood pressure. It works fast and can make a big difference, but it needs careful use because it changes salt, water, and electrolyte balances.

How furosemide works & main uses

The drug blocks salt reabsorption in the kidney’s loop of Henle. That forces the body to dump sodium, chloride, and water, which lowers fluid buildup. For heart failure or pulmonary edema, IV furosemide often brings rapid relief—patients usually pee more within minutes. Orally, it starts working in about 30–60 minutes and lasts around 6–8 hours. Common reasons doctors use it: reduce ankle or leg swelling, ease breathing in fluid-overloaded lungs, and help control blood pressure when other meds aren’t enough.

Practical dosing and safety tips

Typical starting doses vary: oral 20–40 mg once daily is common, with increases to 80 mg or more if needed. In severe fluid overload, IV boluses of 20–40 mg (sometimes higher) are used; in acute pulmonary edema, 40–80 mg IV is a common starting point. People with poor kidney function often need higher doses. Never change dose without advice from your prescriber.

Watch for key side effects: low potassium (hypokalemia), low magnesium, dehydration, low blood pressure and dizziness, and, rarely, hearing damage (ototoxicity) with high or rapid IV doses. Check your electrolytes and kidney function within a few days after starting or changing dose, then regularly after that. If you feel lightheaded, very thirsty, or notice rapid heartbeat or muscle cramps, contact your doctor; those can be signs of electrolyte trouble.

Mind drug interactions: NSAIDs (ibuprofen, naproxen) can blunt furosemide’s effect. Low potassium raises the risk of digoxin toxicity, so combine those drugs carefully. Aminoglycoside antibiotics plus high-dose furosemide increase hearing risk. Diuretics can also affect lithium levels—talk to your prescriber if you take lithium.

Simple habits that help: take furosemide in the morning to avoid nighttime trips to the bathroom, weigh yourself daily to spot fluid changes, and eat potassium-rich foods or use a supplement if your doctor recommends it. Keep hydrated but follow fluid limits set by your clinician when needed.

Furosemide is a powerful, fast-working medicine. It can relieve uncomfortable swelling and breathing problems, but it requires monitoring and respect for dosing rules. If you have questions about your dose, side effects, or how it mixes with other meds you take, reach out to your healthcare team—don’t guess.