Skip to main content

Lasix: 7 things you should know

Medically reviewed by Carmen Fookes, BPharm. Last updated on Nov 9, 2020.

1. How it works

  • Lasix is a brand (trade) name for furosemide. Furosemide significantly increases urination by inhibiting the reabsorption of salts in the kidneys.
  • Lasix belongs to the class of medicines known as loop diuretics.

2. Upsides

  • Used to relieve the body of excess fluid caused by heart failure, kidney failure, cirrhosis of the liver, and other conditions.
  • May be used in addition to other medicines for the treatment of high blood pressure.
  • An injectable form is available.
  • Lasix is available as a generic under the name furosemide.

3. Downsides

If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:

  • Dry mouth, thirst, weakness, muscle pains or cramps, muscular fatigue, dizziness on standing, gastrointestinal disturbances, changes in blood counts, and alterations in cholesterol levels or liver function.
  • Lasix's effect is very strong. It can lead to a significant depletion of electrolytes which may lead to side effects such as muscle cramps and an irregular heartbeat. The risk is greater in people with a restricted salt intake or taking certain medications.
  • Tinnitus and reversible or irreversible hearing impairment have been reported. The risk is greater with higher dosages, injectable Lasix, severe renal impairment, low protein levels, and concomitant therapy with other drugs that are also toxic to the ears.
  • May increase blood glucose levels and affect laboratory test results.
  • Older people may not respond as well to the initial diuretic effect of Lasix.
  • May not be suitable for some people including those with cirrhosis of the liver or ascites, kidney disease, or who are already electrolyte depleted or dehydrated.
  • May interact with a number of other drugs including potassium, lithium, corticosteroids, digoxin, phenytoin, and methotrexate as well as those that also lower blood pressure.

Note: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. View complete list of side effects

4. Bottom Line

Lasix is a strong diuretic that increases urination which relieves excess fluid from the body. This may also lead to the depletion of certain electrolytes, such as potassium.

5. Tips

  • Dosages vary from individual to individual and people taking high dosages may need extra monitoring by their doctor. Some individuals may only need to take Lasix two to four times per week.
  • You may be more sensitive to sunlight while taking Lasix. Use an SPF 30-50+ sunblock when outside.
  • Tell your doctor if you develop diarrhea or vomiting while taking Lasix.
  • Get up slowly when going from a lying down or sitting position to standing because Lasix may make you feel dizzy.
  • Your electrolyte levels will need regular monitoring and your blood may need occasional testing for diabetes. If you already have diabetes, be aware that Lasix may increase your blood glucose levels.
  • Potassium supplements or extra dietary potassium may be needed to counteract the effects of low potassium levels caused by Lasix.

6. Response and effectiveness

  • The onset of diuresis (increased urination) is within an hour.
  • Peak effects are seen within one to two hours and the effects of Lasix last for 6 to 8 hours.

7. Interactions

Medicines that interact with Lasix may either decrease its effect, affect how long it works for, increase side effects, or have less of an effect when taken with Lasix. An interaction between two medications does not always mean that you must stop taking one of the medications; however, sometimes it does. Speak to your doctor about how drug interactions should be managed.

Common medications that may interact with Lasix include:

  • aspirin
  • allopurinol
  • antibiotics, such as cephalexin, gentamicin, neomycin, or tobramycin
  • anticonvulsants, such as phenytoin or fosphenytoin
  • cisplatin
  • cyclosporine
  • duloxetine
  • lithium
  • methotrexate
  • methylphenidate
  • NSAIDs, such as diclofenac, ibuprofen, or indomethacin
  • sucralfate
  • other medications that lower potassium.

People taking oral medications for diabetes may need to talk to their doctor about adjusting the dose of their medicine.

Note that this list is not all-inclusive and includes only common medications that may interact with Lasix. You should refer to the prescribing information for Lasix for a complete list of interactions.


Lasix (furosemide) [Package Insert]. Revised: 04/2019. Validus Pharmaceuticals LLC.

Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use Lasix only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Copyright 1996-2022 Revision date: November 8, 2020.