Key takeaways:
Furosemide (Lasix) is a diuretic (water pill) that helps remove extra fluid from your body. It can also help lower your blood pressure.
Since it’s a diuretic, you can expect to pee more frequently while taking furosemide. It’s best to take it earlier in the day to avoid waking up in the middle of the night.
Other potential furosemide side effects include dizziness, headache, and drops in blood pressure when you change body positions. Rare but serious risks include hearing problems and severe allergic reactions.
You can help lower your risk of several furosemide side effects by standing up slowly, using proper sun protection, and staying hydrated.
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Furosemide (Lasix) is a diuretic (water pill) that has been around for over 50 years. It’s even considered an essential medication by the World Health Organization.
Furosemide is a loop diuretic. It works by removing extra fluids from your body. Because of this, furosemide is used to lower blood pressure and reduce swelling (edema) from certain medical conditions.
If you’ve ever taken a water pill like furosemide, you already know to expect frequent trips to the bathroom. But what are some of the other potential side effects?
Furosemide side effects at a glance
Furosemide side effects can range from mild to severe. Many of the mild side effects can be managed at home. Moderate or severe side effects may require a dosage change, or you may even be instructed to stop taking furosemide.
Mild furosemide side effects include:
Increased urination
Dizziness
Headache
Blurred vision
Nausea
Vomiting
Constipation
Diarrhea
Weakness
Itching
Increased sun sensitivity
Increased blood glucose (sugar)
Increased cholesterol levels
Dehydration and electrolyte changes
Drops in blood pressure when changing body positions (orthostatic hypotension)
Increased uric acid levels and worsening gout
More serious furosemide side effects include:
Changes in liver enzymes
Pancreatitis (inflammation of the pancreas)
Ringing in the ears (tinnitus) and hearing loss
Hematologic (blood) side effects
Serious skin reactions, such as Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), and drug rash with eosinophilia and systemic symptoms (DRESS) syndrome
Below, we take a closer look at eight furosemide side effects and how to manage them.
1. Frequent urination
Furosemide works by increasing your body’s water loss through your kidneys. This excess fluid leaves your body as urine, so you should expect to urinate more frequently when taking furosemide. Remember, this means that the medication is doing what it’s supposed to do.
You’ll likely start urinating more frequently within 1 hour of taking furosemide. This effect can last for up to 8 hours. Plan on having access to a bathroom, especially when you first start taking it. If you're waking up in the middle of the night to go to the bathroom, taking your dose earlier in the day can help.
2. Dizziness
It’s not unusual for blood pressure medications to make you feel dizzy. And furosemide is no exception. Dizziness may occur as your body adjusts to a lower blood pressure. This should improve as you get used to the medication.
Avoid driving or performing other potentially dangerous tasks until you see how furosemide affects you. And use caution when going from lying down or sitting to standing. Changing positions too quickly when taking furosemide may cause you to faint. Speak with your healthcare team if your dizziness becomes bothersome or doesn’t go away over time.
3. Headache
Similar to dizziness, blood pressure medications can commonly cause headaches. These should go away without treatment as your body gets used to the medication.
Over-the-counter pain relievers, such as acetaminophen (Tylenol), may help provide relief. But it’s best to check with your healthcare team on whether or not OTC pain relievers are safe for you to take. You should also let them know if your headaches don’t go away over time or if they get worse.
4. Blood pressure changes
Drops in blood pressure can happen if you’re changing positions quickly (such as going from sitting to standing) while taking furosemide. This drop in blood pressure may make you feel dizzy, and can cause you to faint. Be sure to stand up slowly to allow your body to adjust and to prevent falls.
Furosemide can be taken on its own for high blood pressure. It can be combined with other blood pressure medications, too. But it’s possible for your blood pressure to get too low (called hypotension) while taking it.
This is more likely to happen if you’re taking furosemide with angiotensin converting enzyme (ACE) inhibitors or angiotensin II receptor blockers (ARBs). Your healthcare team may have you monitor your blood pressure at home. And they may need to adjust the dosage of either medication if they recommend taking them together.
Seek medical attention if you faint, feel severely weak, confused, or have trouble breathing at any point while taking furosemide. These may be signs of dangerously low blood pressure and should be treated right away.
5. Sun sensitivity
If you’re taking furosemide, you’ll need to be extra careful in the sun. That’s because you’re more likely to get a painful sunburn or rash.
You can reduce your risk of sun damage while taking furosemide by:
Staying in the shade when possible
Covering up with long sleeves, sunglasses, and a hat
Applying sunscreen with SPF 30 or higher
Get medical attention right away if you develop a severe sunburn or blistering rash, especially if you also have nausea, vomiting, fever, or confusion. These could be signs of a serious reaction that may require medical attention.
6. Dehydration and electrolyte imbalance
Furosemide causes water and electrolyte loss through your urine. This can cause serious side effects if you take too much furosemide, or if you don’t stay adequately hydrated while taking it.
Signs and symptoms that you may be dehydrated or have an electrolyte imbalance include:
Symptoms such as fainting, dark urine, or a fast heart rate can indicate severe dehydration. Go to the nearest ER if these symptoms develop.
It is important to keep hydrated while taking furosemide. But it’s also possible to drink too much water, especially if you have certain health conditions. Talk to your healthcare team about how much water you should be drinking while taking furosemide.
7. Hearing problems
In rare cases, furosemide can cause hearing problems (ototoxicity). This can present as reversible or irreversible ringing in the ears or hearing loss.
Hearing problems are more likely to occur with furosemide if you:
Take other medications that can cause hearing problems (such as aminoglycoside antibiotics or other loop diuretics)
Take higher-than-recommended doses
Have severe kidney problems
Are receiving high doses of intravenous (IV) furosemide
Let your healthcare team know right away if you notice hearing problems while taking furosemide. They might switch you to a different medication, but don’t stop taking it on your own.
8. Allergic reactions
If you have a sulfa allergy, you might have an allergic reaction to furosemide. That’s because furosemide has a similar structure to sulfa antibiotics. The risk tends to be low, but still requires caution.
Let your healthcare team know if you notice skin hives or a rash when taking furosemide. And if you have systemic lupus erythematosus, furosemide may make your symptoms worse.
Serious allergic reactions to furosemide that require emergency medical attention include:
Face, lip, or throat swelling
Difficulty breathing
Skin reactions such as Stevens-Johnson syndrome and toxic epidermal necrolysis
If you need a loop diuretic but have had a severe allergic reaction, there’s an alternative. Ethacrynic acid (Edecrin) doesn’t contain sulfa and is often used by people with a sulfa allergy.
Frequently asked questions
There aren’t any specific foods you need to avoid while taking furosemide. But it’s a good idea to limit high-sodium foods, such as processed meats, canned soups, and salty snacks. Too much sodium can make the medication less effective and worsen fluid retention. It’s also best to avoid alcohol and excessive caffeine consumption.
Your healthcare team can give you dietary recommendations based on your specific needs.
Furosemide helps your body get rid of extra fluid, but staying hydrated is still important. Don’t overdo it, though. Drinking too much water can throw off your electrolyte balance. Follow your healthcare team’s guidance on how much fluid to drink each day.
Yes, furosemide is commonly used to reduce swelling in the legs caused by fluid buildup. It works by helping your kidneys remove excess water and salt through your urine. If your swelling doesn’t improve or gets worse, let your healthcare team know.
There aren’t any specific foods you need to avoid while taking furosemide. But it’s a good idea to limit high-sodium foods, such as processed meats, canned soups, and salty snacks. Too much sodium can make the medication less effective and worsen fluid retention. It’s also best to avoid alcohol and excessive caffeine consumption.
Your healthcare team can give you dietary recommendations based on your specific needs.
Furosemide helps your body get rid of extra fluid, but staying hydrated is still important. Don’t overdo it, though. Drinking too much water can throw off your electrolyte balance. Follow your healthcare team’s guidance on how much fluid to drink each day.
Yes, furosemide is commonly used to reduce swelling in the legs caused by fluid buildup. It works by helping your kidneys remove excess water and salt through your urine. If your swelling doesn’t improve or gets worse, let your healthcare team know.
The bottom line
Furosemide (Lasix) side effects include frequent urination, headaches, and dizziness. It can also cause drops in blood pressure when changing positions (like from sitting or laying down to standing) and make you more sensitive to the sun. In rare cases, hearing loss and severe allergic reactions may also occur.
Talk to your prescriber or pharmacist if you have any questions about furosemide side effects and how to manage them.
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References
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Khan, T. M., et al. (2023). Furosemide. StatPearls.
Labib, A., et al. (2023). Toxic epidermal necrolysis. StatPearls.
Ponka, D. (2006). Approach to managing patients with sulfa allergy. Canadian Family Physician.
U.S. Food and Drug Administration. (2021). High blood pressure.
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U.S. Food and Drug Administration. (2025). All approvals and tentative approvals July 1966.
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