Furosemide (Lasix) is a generic prescription medication. As with other drugs, it can cause side effects, which are also called adverse effects. Furosemide is used to treat:
- high blood pressure in adults
- edema related to certain heart, liver, and kidney problems in some adults and children
Furosemide comes as an oral tablet. (You may also hear it referred to as a water pill.) Furosemide also comes in other forms, including an injectable and oral solution, but this article does not cover them. For more about these forms, ask your doctor.
Read on to learn about potential common, mild, and serious side effects. For a general overview of furosemide, including details about its uses, refer to this article. Your doctor can also tell you more about furosemide.
Furosemide can cause certain side effects. Some of these are more common than others. The side effects may be temporary, lasting a few days to weeks. However, if the side effects last longer than that, bother you, or become severe, be sure to talk with your doctor or pharmacist.
These are just a few of the more common side effects reported by people who took furosemide in clinical trials:
Mild side effects can occur when taking furosemide. This list doesn’t include all possible mild side effects of the drug. For more information, you can refer to furosemide’s prescribing information.
Mild side effects that have been reported with furosemide include:
- muscle pain or cramping, such as leg cramps
- nausea or vomiting
- diarrhea or constipation
- ringing in the ears
- blurry vision
- skin rash
- sun sensitivity
- high levels of cholesterol or triglycerides
- urinating more often than usual
- dry mouth
- mild allergic reaction*
These side effects may be temporary, lasting a few days to weeks. However, if the side effects last longer than that, bother you, or become severe, be sure to talk with your doctor or pharmacist.
Note: After the Food and Drug Administration (FDA) approves a drug, it tracks side effects of the medication. If you develop a side effect while taking furosemide and want to tell the FDA about it, visit MedWatch.
* For more information about this side effect, see “Furosemide: Side effect specifics” below.
Furosemide may cause serious side effects, but they aren’t common. The list below may not include all possible serious side effects of the drug. For more information, you can refer to furosemide’s prescribing information.
If you develop serious side effects while taking furosemide, call your doctor right away. If the side effects seem life threatening or you think you’re having a medical emergency, immediately call 911 or your local emergency number.
Serious side effects that have been reported and their symptoms include:
- Liver problems, such as increased levels of liver enzymes (which would be noticed in a blood test) or jaundice. Symptoms of jaundice can include:
- yellowing of the skin and white of the eyes
- pale stool
- dark urine
- Kidney damage. Symptoms can include:
- urinating more or less often than usual
- swelling of the legs or feet
- Changes in the levels of chemicals called electrolytes, such as low sodium levels. Symptoms can include:
- nausea or vomiting
- Pancreatitis (inflammation of the pancreas). Symptoms can include:
- abdominal pain
- nausea or vomiting
- Changes in blood cell levels, such as low levels of red blood cells or platelets. Symptoms can include:
- bruising easier than usual
- Serious skin reactions, such as Stevens-Johnson syndrome or toxic epidermal necrolysis. Symptoms can include:
- skin peeling or blistering
- Hearing loss.
- Risk of dehydration.*†
- Low potassium levels.†
- Orthostatic hypotension.†
- Severe allergic reaction.†
Furosemide is approved for use in certain children to help treat edema (also called water or fluid retention). Most children taking furosemide will experience side effects similar to those in adults.
However, children may have an increased risk of certain side effects, including kidney problems. Furosemide can cause calcium to build up in the kidneys, which can lead to kidney stones or kidney damage. The increased risk was seen in clinical trials when the drug was given to children ages 4 years or younger.
In addition, premature babies given furosemide may have heart problems, such as patent ductus arteriosus. (This is a hole in that heart that doesn’t close properly.)
If your child is prescribed furosemide, talk with their doctor about what side effects may occur.
Side effects of furosemide may vary, depending on which strength of the medication you take. Furosemide oral tablets come in the following strengths: 20 milligrams (mg), 40 mg, and 80 mg.
Taking a higher dose of furosemide exposes your body to more medication. And if you have more medication in your system, the risk of side effects can increase. For example, the 80-mg strength of furosemide has a higher risk of causing side effects than the 20-mg strength.
Your doctor can advise you on what strength of furosemide is right for you.
In clinical trials, furosemide side effects in older adults (people ages 65 years and older) were the same as those in younger people.
However, older adults may have a higher risk of side effects. As you get older, your body breaks down medications more slowly. This can cause furosemide to build up in your system, which could expose you to more of the drug.
Because of this, doctors will usually first prescribe the lowest possible dose of furosemide for older adults. This is 20 milligrams (mg). The risk of side effects with the 20-mg strength is lower than with a higher strength of furosemide.
If you’re an older adult and considering taking furosemide, talk with your doctor about the best strength and dosage for you.
Furosemide may cause several side effects. Here are some frequently asked questions about the drug’s side effects and their answers.
What complications could furosemide cause?
It’s possible for furosemide to cause certain complications, some of which may be serious and cause long-term side effects. These may include:
If you’re concerned about possible complications from furosemide treatment, talk with your doctor or pharmacist.
Do side effects of Lasix and furosemide differ?
Side effects of Lasix and furosemide are not expected to differ.
Lasix is the brand-name version of the generic drug furosemide. This means that both medications contain the same active ingredient: furosemide. Because the two drugs have the same active ingredient, they should cause similar side effects.
However, Lasix and furosemide may have different inactive ingredients. These are ingredients that are mixed in with the active ingredient and don’t have a medical effect. Inactive ingredients may include fillers, flavorings, and coatings. In some cases, brand-name and generic drugs may cause different reactions due to variations in the inactive ingredients.
If you’d like to learn more about Lasix and furosemide, talk with your doctor or pharmacist.
Learn more about some of the side effects that furosemide may cause. To find out how often side effects occurred in clinical trials, see the prescribing information for furosemide.
Risk of dehydration
It’s possible for furosemide to cause dehydration. In fact, the drug has a
Furosemide is a diuretic, which means it works to eliminate water from your body. This can help with high blood pressure as well as weight gain that’s related to edema. However, too much furosemide may cause your body to get rid of too much water. This can lead to dehydration and low levels of chemicals called electrolytes. It’s not known how often dehydration occurred in clinical trials.
What you can do
Your doctor may first prescribe a low dose of furosemide to see how the drug affects you. Then they can slowly adjust your dose over time to reach the right amount for you.
Starting with a low dose of furosemide can decrease your risk of dehydration. However, if you notice symptoms of dehydration during your treatment, talk with your doctor. These symptoms can include dry mouth, dizziness, headache, and urinating less often than usual.
If your doctor finds that you’re dehydrated, they can recommend a suitable treatment. They may advise that you drink clear fluids, such as water or sports drinks. In some cases, you may need fluids given through an IV.
Low potassium levels
Symptoms of low potassium levels may include:
What you can do
Your doctor will monitor your potassium levels throughout your treatment with furosemide. They may help prevent them from dropping too low.
However, if you develop symptoms of low potassium levels, talk with your doctor right away. If your levels are too low, they may recommend changes to your diet.
Your doctor may also prescribe other medications to help manage your potassium levels. For example, they may recommend potassium supplements or another diuretic, such as spironolactone (Aldactone). Spironolactone can cause hyperkalemia (high potassium levels), which may help balance low potassium levels caused by furosemide.
It’s possible to develop a side effect called orthostatic hypotension while taking furosemide. Orthostatic hypotension is low blood pressure that occurs when changing positions, such as standing up after lying down. It wasn’t reported how often orthostatic hypotension occurred in clinical trials.
Symptoms of orthostatic hypotension may include:
- blurry vision
What you can do
If you develop symptoms of orthostatic hypotension, talk with your doctor.
You may have an increased risk of this side effect if you drink alcohol or take certain other medications, such as barbiturates or opioids, with furosemide. To help lower your risk, your doctor may talk with you about any drugs you take.
In addition, your doctor may recommend that you change positions slowly after sitting or lying down. This may help prevent orthostatic hypotension. Your doctor may also suggest other ways to limit the side effect.
Headaches may occur with furosemide. It wasn’t reported how often headaches occurred in clinical trials of people taking this medication.
It’s important to note that headaches may also be a symptom of serious side effects of furosemide. These include:
- Dehydration. Furosemide has a
boxed warningabout the risk of dehydration. This is a serious warning from the FDA. For details, see “Risk of dehydration” above.
- Changes in electrolyte levels, such as low potassium levels. To learn more, see “Low potassium levels” above.
What you can do
If you experience headaches while taking furosemide, talk with your doctor. They may order blood tests to see if you’re dehydrated or experiencing other side effects.
In some cases, your doctor may recommend treatment for your headaches. For example, they may suggest taking an over-the-counter medication, such as acetaminophen (Tylenol).
As with most drugs, furosemide can cause an allergic reaction in some people.
Symptoms can be mild or serious and can include:
- skin rash
- swelling under your skin, typically in your eyelids, lips, hands, or feet
- swelling of your mouth, tongue, or throat, which can make it hard to breathe
What you can do
For mild symptoms of an allergic reaction, call your doctor right away. They may recommend ways to ease your symptoms and determine whether you should keep taking furosemide. However, if your symptoms are serious and you think you’re having a medical emergency, immediately call 911 or your local emergency number.
Before starting treatment with furosemide, talk with your doctor about any medical conditions that you have. They can help determine whether furosemide may be a safe treatment option for you.
Boxed warning: Risk of dehydration
Be sure to talk with your doctor about your health history before you take furosemide. This drug may not be the right treatment for you if you have certain medical conditions or other factors that affect your health. These are considered drug-condition or drug-factor interactions. The conditions and factors to consider include:
Electrolyte problems. Furosemide may cause electrolyte problems. If you already have a condition that affects your electrolyte levels, be sure to tell your doctor. Furosemide may worsen it. Your doctor may monitor your electrolyte levels more often. In some cases, they may recommend a different treatment.
Liver problems. It’s possible for furosemide to increase your risk of liver problems. If you have an existing liver condition, such as cirrhosis, taking furosemide may worsen it. Before starting furosemide treatment, tell your doctor whether you have a liver condition. They may monitor your liver more frequently.
Diabetes. It’s possible for furosemide to increase your blood sugar levels, but this is rare. If you have type 1 or type 2 diabetes, a rise in the levels may make your condition worse. Before taking furosemide, be sure to tell your doctor whether you have diabetes. They may recommend monitoring your blood sugar levels more often.
Allergic reaction. If you’ve had an allergic reaction to furosemide or any of its ingredients, your doctor will likely not prescribe furosemide.
Your doctor also won’t usually prescribe furosemide if you’ve had an allergic reaction to drugs called sulfonamides. If you’re allergic to these medications, you might be allergic to furosemide.
Taking furosemide could cause you to have another allergic reaction. Ask your doctor what other treatments may be better options for you.
Bladder or urinary problems. Furosemide is a diuretic, which means it will cause you to urinate more often than usual. If you have a bladder or urinary problem, taking this medication may worsen your condition. (Examples of bladder and urinary problems include benign prosthetic hyperplasia and urinary retention.) Before starting treatment with furosemide, tell your doctor about any bladder or urinary problems you have. They may monitor you more often than usual.
Kidney problems. Kidney problems, such as chronic kidney disease, may cause furosemide to build up in your body. This can increase your risk of side effects. Before starting treatment with furosemide, tell your doctor about any kidney problems you have. They may prescribe a lower dose to see how the drug affects you. Then your doctor can adjust your dose over time to reach the amount that’s right for you.
Thyroid problems. High doses of furosemide may worsen thyroid conditions. If you have a thyroid problem, such as low levels of thyroid hormones, tell your doctor before taking the drug. They may monitor the levels of thyroid hormones in your blood more often while you’re taking furosemide.
Alcohol with furosemide
There aren’t any known interactions between furosemide and alcohol. However, drinking alcohol while taking furosemide may increase your risk of side effects, including:
- nausea or vomiting
- blurry vision
- orthostatic hypotension (low blood pressure that occurs when changing positions, such as standing up after lying down)
- liver problems, such as increased levels of liver enzymes (which can be a sign of liver damage)
Both furosemide and alcohol can cause these side effects, so combining the two substances may further increase your risk.
If you’d like to drink alcohol while taking furosemide, talk with your doctor to see how much, if any, is safe for you.
Pregnancy and breastfeeding while taking furosemide
It’s unknown whether it’s safe to take furosemide during pregnancy or while breastfeeding.
Furosemide hasn’t been studied in pregnant people, so it’s not known for sure what effects the drug may have on a developing fetus. Animal studies show that furosemide may increase the risk of high birth weight, pregnancy loss, or, in some cases, death of the pregnant animal. However, animal studies don’t always indicate what may happen in humans.
Furosemide passes into breast milk, which means a breastfed child would be exposed to the drug. It’s unknown what effects the drug may have on a child who is breastfed. Furosemide may also block lactation (the production and release of breast milk). This can make it difficult to breastfeed.
If you’re pregnant or planning to become pregnant, talk with your doctor. You should also talk with them if you’re breastfeeding or thinking about it. Your doctor can advise you on whether furosemide or a different treatment is right for you.
In most cases, side effects that occur with furosemide are mild. However, it’s possible for serious side effects to occur, too. Be sure to talk with your doctor if you develop any serious side effects. If furosemide works for you, your doctor may recommend that you take it long term.
If you’d like to learn more about furosemide, talk with your doctor or pharmacist. They can help answer any questions you have about side effects from taking the drug.
Referring to the following articles about furosemide can provide you with additional information:
- More information about furosemide. For details about other aspects of furosemide, refer to this article.
- A look at your condition. For details about your condition, see our cardiovascular health hub and this list of kidney disease articles.
Disclaimer: Medical News Today has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.