What Is Furosemide? Uses, Dosage, and What You Need to Know in 2026

Furosemide is one of the most commonly prescribed medications in the United States. In 2023, it ranked as the 29th most prescribed drug with over 19 million prescriptions. Known by its brand name Lasix, furosemide is what doctors call a "loop diuretic"—or more simply, a water pill. Here's everything you need to know about it.

What Is Furosemide?

Furosemide is a loop diuretic—a type of medication that makes your kidneys produce more urine, removing excess fluid from your body. It's been in use since 1966 and is on the World Health Organization's List of Essential Medicines. It is available as an inexpensive generic and under the brand names Lasix, Furoscix, and Lasix ONYU.

Furosemide is NOT a controlled substance. It can be prescribed by any licensed prescriber—primary care doctors, cardiologists, nephrologists, nurse practitioners, and physician assistants. Refills are generally straightforward.

What Is Furosemide Used For?

The FDA has approved furosemide to treat:

Edema from heart failure: When the heart doesn't pump efficiently, fluid backs up in the lungs and body. Furosemide removes this excess fluid, relieving swollen legs, ankles, and feet, and reducing shortness of breath.

Edema from liver cirrhosis: Liver disease can cause fluid to accumulate in the abdomen (ascites) and body. Furosemide is often used alongside spironolactone.

Edema from kidney disease: Conditions like nephrotic syndrome cause protein loss and fluid retention. Furosemide helps remove the excess fluid.

High blood pressure (hypertension): Furosemide lowers blood pressure by reducing fluid volume. It's typically used when thiazide diuretics haven't worked or when the patient also has kidney or heart disease.

Off-label (not FDA-approved but clinically used): hypercalcemia (high calcium), acute pulmonary edema (fluid in the lungs), and ascites from cancer.

What Forms Does Furosemide Come In?

Oral tablets: 20 mg, 40 mg, and 80 mg. This is the most common form.

Oral solution: 10 mg/mL liquid, used for patients who cannot swallow tablets.

Injectable (IV/IM): 10 mg/mL solution for hospital/clinical use. IV furosemide is twice as potent as oral.

Furoscix (subcutaneous kit): 80 mg/10 mL prefilled cartridge delivered through an on-body infusor under the skin. Used at home by some heart failure patients.

Typical Furosemide Doses

Doses vary significantly based on your condition, kidney function, and clinical response:

For edema (adults): Starting dose is 20–80 mg once daily. May increase by 20–40 mg every 6–8 hours as needed. Maximum 600 mg/day.

For hypertension (adults): 40 mg twice daily initially, adjusted based on blood pressure response.

For children (over 1 month): 2 mg/kg per dose, increased by 1–2 mg/kg every 6–8 hours; maximum 6 mg/kg.

Your dose is set by your doctor based on your specific condition. Never adjust your dose without consulting your prescriber.

How to Take Furosemide

With or without food: Furosemide can be taken with or without food. Taking it with food or milk helps reduce stomach upset.

Timing: Take in the morning to avoid nighttime urination. If twice daily, take the second dose no later than 5 PM.

Onset: Furosemide starts working within 1 hour orally. You'll produce noticeably more urine during the first 4–6 hours.

Missed dose: Take as soon as you remember. If it's close to your next dose, skip the missed dose. Never double up.

Sucralfate interaction: If you take sucralfate (Carafate), take it at least 2 hours before or after furosemide—sucralfate can reduce furosemide's effectiveness.

Important Warnings

Do not use furosemide if you cannot urinate (anuria)

Tell your doctor if you have a sulfa allergy before starting

Monitor your weight daily if prescribed for heart failure—report a gain of 2+ lbs overnight to your doctor

Keep all lab appointments—furosemide requires regular monitoring of kidney function and electrolytes

Learn more about furosemide side effects and what to expect.

If you're struggling to fill your furosemide prescription, medfinder can locate a nearby pharmacy with your medication in stock.