8 Furosemide Side Effects You Should Know About
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.
As a diuretic, you can expect to pee more frequently while taking furosemide. Avoid taking it late in the day so you’re not having to wake up in the middle of the night.
You can help lower your risk of several furosemide side effects by standing up slowly, using proper sun protection, and staying hydrated.
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 works by removing extra fluids from your body. It’s considered a loop diuretic, and because of how it works, it’s 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 side effects?
1. Frequent urination
Furosemide works by increasing 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 one hour of taking furosemide. This effect can last up to 8 hours. Plan on having access to the restroom, especially when you first start taking it. If you're waking up in the middle of the night to hit the restroom, 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 can happen as your body adjusts to a lower blood pressure. This should improve as you get used to the medication.
Avoid driving or operating other heavy machinery until you see how furosemide affects you. And use caution when going from lying down or sitting to standing. Changing positions too quickly may cause you to faint. Speak with your healthcare provider if 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, like acetaminophen (Tylenol) or ibuprofen (Advil, Motrin), may help provide relief. But it’s best to check with your healthcare provider on whether they’re safe for you to take. You should also let them know if your headaches don’t go away or get worse.
4. Blood pressure changes
Drops in blood pressure can happen if you’re changing positions quickly (like sitting to standing) while taking furosemide. This can make you feel dizzy, and possibly cause you to faint. Getting up slowly can help.
Furosemide can be taken on its own for high blood pressure. And 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 may be more likely to happen if you’re taking furosemide with angiotensin converting enzyme (ACE) inhibitors or angiotensin II receptor blockers (ARBs). Your healthcare provider may have you monitor your blood pressure levels at home. And they may need to adjust your dosage of either medication if you need to take them together.
5. Sun sensitivity
If you’re taking furosemide, it’s important 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 by:
Staying in the shade
Covering up with long sleeves, sunglasses, and a hat
Using SPF 30 or higher sunscreen
If you need help picking out the right sunscreen for you, check out our video guide here.
6. Dehydration and electrolyte imbalance
As we’ve discussed, furosemide works by promoting 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.
Signs and symptoms that you may be dehydrated or have an electrolyte imbalance include:
But you also don’t want to drink too many fluids. You’re likely taking furosemide to help your body get rid of extra fluids. But it’s still important to get enough fluids to remain hydrated. Talk to your healthcare provider about how much water should you 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 with furosemide if you:
Take other medications that can cause hearing problems (like 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 provider know right away if you notice hearing problems while taking furosemide. They may have you switch to a different medication. But don’t stop taking it on your own.
8. Allergic reactions
If you have a sulfa allergy, it’s possible to 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 provider 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 that require emergency medical attention include:
Face, lip, or throat swelling
Difficulty breathing
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.
The bottom line
Furosemide is a common medication used to treat swelling if you have heart failure, cirrhosis, or kidney problems. It also helps lower blood pressure.
Frequent urination is a common furosemide side effect. But this means the medication is working. Taking it earlier in the day can help you avoid waking up in the middle of the night to pee.
Make sure your healthcare provider has your updated allergy list. While rare, people with a sulfa allergy can also have an allergic reaction to furosemide.
Why trust our experts?
References
Gallagher, K. L., et al. (1979). Furosemide-induced ototoxicity. Annals of Internal Medicine.
Khan, T. M., et al. (2022). Furosemide. StatPearls.
Labib, A., et al. (2021) Toxic epidermal necrolysis. StatPearls.
PD-Rx Pharmaceuticals, Inc. (2022). Furosemide [package insert].
Ponka, D. (2006). Approach to managing patients with sulfa allergy: use of antibiotic and nonantibiotic sulfonamides. Canadian Family Physician.
U.S. Food and Drug Administration (2015). The sun and your medicine.
U.S. Food and Drug Administration. (2021). High blood pressure.
U.S. Food and Drug Administration. (2022). All approvals and tentative approvals July 1966.
World Health Organization. (2021). WHO model list of essential medicines.
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