Furosemide has a boxed warning. A boxed warning is the strongest safety-related warning issued by the US Food and Drug Administration (FDA). This medication is a potent diuretic that can significantly affect the fluid balance in your body. Taking a large dose can result in severe dehydration or an imbalance of electrolytes. Amounts should be specific to the patient’s case and condition.¹
Furosemide, a diuretic, targets the kidneys to facilitate the excretion of excess fluid and salt from the body through urine.
Various medical conditions cause water retention, which leads to swelling or edema. Water retention and the development of fluid overload strain the cardiovascular system, which can have detrimental effects on numerous crucial functions within the body.² ³
Furosemide belongs to a subgroup called loop diuretics because it primarily targets a structure in the kidneys called the loop of Henle to prevent sodium and chloride retention. The actions of the drug cause those electrolytes to be excreted in the urine. Water accompanies sodium out of the body, leading to increased urination or diuresis.
Furosemide is US FDA-approved for treating a range of conditions that cause edema (swelling caused by excess fluid) and elevated blood pressure in children and adults.
Conditions that may be treated with furosemide include:⁴
Congestive heart failure
Kidney disease and failure
Liver diseases, such as cirrhosis and ascites
Acute pulmonary edema (as an adjunct medication)
The drug can also be used as a second-line agent for treating high blood pressure, mainly when it results from one of the above conditions.
Doctors sometimes prescribe furosemide for other situations, including the prevention and treatment of bronchopulmonary dysplasia in premature babies and in palliative care. However, these uses are not approved by the US FDA.⁵ ⁶
Furosemide is available in several forms and strengths. Your doctor will determine the appropriate form, dose, and dosing schedule for you.⁷
Tablets (generic, Lasix) are available in three strengths:⁸ ⁹
The oral solution (generic) is available in two concentrations:¹¹
The injectable form for IV use (generic) is available in one strength:¹¹
A self-administered injectable formulation (Furoscix) is available in one concentration for subcutaneous administration:¹²
80mg/10mL (in a single-use pre-filled cartridge)
The appropriate dose depends on several factors, including the condition being treated, your body’s handling of the medicine, any other health concerns you have, other medications you take, your age, your body weight, and others. Furosemide can be used in pediatric, geriatric, and adult patients for the conditions indicated by the US FDA.
The injectable form for IV use is administered in a medical setting, while the other forms are self-administered at home. If you take one of the self-administered forms, carefully read and follow the directions provided by your pharmacist and doctor. You can take the medication with or without food, but research has shown that furosemide is more effective when taken before meals. In most instances, furosemide is taken once a day or every 12 hours, depending on your doctor's instructions.¹³
The amount of time it takes for furosemide to work varies based on the medical condition being treated and other factors affecting the body’s handling of the drug. It also depends on the route of administration.
When taken orally, furosemide’s effects are apparent within an hour and peak in 60–90 minutes. After an intravenous administration, the drug works very quickly, reaching peak effectiveness in 30 minutes. Some patients only need one dose of furosemide for an acute problem, while others may require a longer course of daily dosing to treat a chronic disease like hypertension.¹⁴
Furosemide may trigger severe adverse reactions or worsening symptoms in people with certain conditions.
You may not be able to take furosemide or must take it cautiously if you have:¹⁵
Furosemide can cause side effects ranging from minor to severe.¹⁶
Commonly reported side effects include the following:
Diarrhea or constipation
Loss of appetite
Skin rash, itching
Increased blood glucose levels
Furosemide can cause changes in the blood levels of important electrolytes and other abnormalities, particularly in patients with the following medical conditions:¹⁷
Hypokalemia (low potassium levels)
Hyponatremia (low sodium levels)
Elevated blood urea nitrogen (BUN) levels, especially in association with dehydration
Increased blood sugar levels
Low calcium and magnesium levels
Worsening symptoms in patients with systemic lupus erythematosus
Increased uric acid levels (may affect patients with gout)
Low blood albumin (protein) levels (may increase toxic effects involving the ear)
In some people, furosemide triggers dangerous side effects and symptoms. If you experience any of the following, seek immediate medical attention:
Decrease in urination
Fatigue or drowsiness
Rapid heart rate
Nausea or vomiting
Painful muscle cramps
Severe rash or peeling skin
Ringing in the ears or impaired hearing
Monitor for unusual symptoms while taking furosemide, and note any changes that may indicate a problem. If your side effects persist or worsen, you should speak with your doctor.
An overdose of furosemide is possible, but the threshold for how much drug causes an overdose will be different in each person. The dangers of a furosemide overdose are the effects the medication can have on the body's processes, including kidney functioning and blood pressure regulation.
Symptoms of toxicity from an overdose of furosemide include any of the following:
Dry mouth and extreme thirst
Severe fatigue and weakness
Abdominal cramps or vomiting
Dizziness or vertigo
Fainting or loss of consciousness
If you think you might have taken too much furosemide, call the National Poison Control helpline at 1-800-222-1222. If your symptoms are severe, call 911 or go to your nearest emergency department.
Some people are allergic to furosemide. In rare cases, the drug could cause an anaphylactic reaction, which is life-threatening. Allergic reactions require prompt medical care to counteract their progressive effects on the body.¹⁸
Signs of a severe allergic reaction or anaphylaxis can include any of the following:¹⁹
Tightening or closing of the throat
Difficulty breathing or wheezing
Swelling of the face, tongue, lips, or mouth
Breaking out into hives
Itching of the skin or mouth
Severe rash with peeling skin
Increased heart rate
Loss of consciousness
Furosemide can be used short- or long-term to treat a medical condition causing hypertension or edema. How long you need to take furosemide depends on the extent of your illness and whether it resolves or continues for a longer period. Taking the medication as prescribed reduces the risk of developing adverse outcomes associated with your medical condition.
As with many other medications, the long-term use of furosemide can have unwanted effects, including the following:²⁰
Electrolyte abnormalities like hypokalemia (low potassium levels)
Increased blood sugar
Thyroid hormone deficiency
Low blood pressure (primarily in older individuals)
Your physician will likely order regular lab tests to monitor for the development of any of these conditions if you take furosemide for an extended time.
Furosemide has been designated a pregnancy category C drug by the US FDA. Animal studies have demonstrated negative effects on the fetus, but there are no adequate studies on the impact of the drug on pregnant women.²² ²³
Your doctor will weigh the risks of not treating your condition during pregnancy, such as the effects of worsening heart failure or liver disease, against the potential risks of taking furosemide. Your doctor may recommend an alternate therapy that has proven safe and effective for pregnant women. If you need to take furosemide while pregnant, you’ll need to take measures to prevent severe dehydration to ensure adequate blood flow to the fetus.²⁴
Furosemide has been shown to be present in breast milk, but there is a lack of information regarding the drug’s effects on the infant. Higher doses might affect lactation. Discuss the potential risks with your doctor before using furosemide while breastfeeding.²⁵ ²⁶
If you miss a dose of furosemide, take it as soon as you remember unless it’s nearly time for your next dose. If that’s the case, skip the missed one and take your next dose as scheduled. Never double your dose to make up for a missed one.
Certain prescription drugs, over-the-counter medications, and other substances, including herbal supplements and vitamins, may interact with furosemide negatively or trigger unwanted side effects.
Substances that may interact with furosemide include:²⁷
Aminoglycoside antibiotics, such as amikacin, gentamicin, neomycin, and tobramycin (Bethkis, Tobi)
Anti-cancer medicines, such as naxitamab (Danyelza) and vandetanib (Caprelsa)
Antidepressants like isocarboxazid (Marplan), selegiline, and other monoamine oxidase inhibitors (MAOIs)
Anti-inflammatories like mefenamic acid and aspirin
Anti-seizure medicines, such as fenfluramine (Fintepla) and phenytoin (Dilantin)
Attention-deficit/hyperactivity disorder (ADHD) medicines like dextroamphetamine (Adderall, Dexedrine), dexmethylphenidate (Focalin), lisdexamfetamine (Vyvanse), viloxazine (Qelbree), and methylphenidate (Ritalin)
Asthma drugs, such as albuterol (Proventil) and formoterol (Symbicort)
Blood pressure medicines:
Cannabis-derived medications, such as dronabinol (Marinol)
Corticosteroids, such as dexamethasone (Decadron), betamethasone (Celestone), hydrocortisone, and prednisolone
Ethacrynic acid (Edecrin)
Hormones like testosterone, hydroxyprogesterone, and estradiol
Migraine medications, including dihydroergotamine (DHE), ergotamine (Cafergot), and sumatriptan (Imitrex)
Weight-loss drugs, such as phentermine (Lomaira) and phendimetrazine
Other substances, including caffeine and licorice
This list of interactions is not exhaustive. Provide your doctor with a list of all medicines, herbs, and supplements you take before starting furosemide.
Drinking alcohol may not directly interact with furosemide, but mixing the two could increase the risk of dehydration, as both are diuretics. It may also cause an increased risk of orthostatic hypotension (a sudden drop in blood pressure associated with transitioning from a seated or lying position to standing) or other side effects. Speak with your doctor about whether alcohol is safe in your case while you are taking furosemide.²⁸
Furosemide is available by prescription only, so you’ll need to meet with your doctor before you start taking it. At your appointment, you should discuss the following topics:²⁹ ³⁰
Your medical conditions, especially liver or kidney disease, diabetes, gout, or systemic lupus erythematosus
All medications, herbs, and supplements you take regularly or occasionally
Any past adverse reactions to medications
Upcoming surgical and dental procedures, particularly if you plan to have coronary artery bypass grafting (CABG)
If you’re pregnant, trying to conceive, or breastfeeding
How and when you should stop taking furosemide depends on the medical condition being treated and your doctor’s assessment. If your acute condition has resolved, you may be able to discontinue it with your doctor’s guidance. However, if furosemide is part of a long-term treatment plan to reduce your blood pressure or improve the symptoms of heart or liver disease, stopping the medication could have severe adverse effects.
1982: Furosemide earned US FDA approval³¹
1999: The US FDA approved furosemide in the injectable form³²
2022: The US FDA approved Furoscix, the self-administered subcutaneous injectable form of furosemide³³
If you are taking furosemide, keep the following tips in mind:
Take your medication according to your doctor's instructions. If you’re unsure about something, ask your doctor or pharmacist for clarification.
Avoid excess exposure to sunlight and wear sunscreen and protective clothing, as furosemide can cause light sensitivity.³⁴
Follow your doctor’s guidance regarding lifestyle and dietary changes to help improve your condition.
Take your time when standing up from a sitting or lying down position, as furosemide can make you feel lightheaded, particularly when starting the medicine or after dose increases.
Some people are more sensitive to the sun while taking furosemide. You should always take the necessary measures to protect your skin from the sun, but you may need to be extra cautious while taking this medication. Avoid prolonged exposure and wear sunscreen, protective clothing, and a hat when you’re outside.
If you are having surgery or a medical procedure, speak with your prescribing doctor and the surgeon about whether you may need to alter or stop taking furosemide. Do not change your medication dose or stop taking it until you have received your doctor’s instructions.³⁵
Here at HealthMatch, we’ve done our best to ensure that the information provided in this article is helpful, up to date, and, most importantly, accurate.
However, we can’t replace the one-to-one advice of a qualified medical practitioner or outline all of the possible risks associated with this particular drug and your circumstances.
It is therefore important for you to note that the information contained in this article does not constitute professional medical or healthcare advice, diagnosis or recommendation of treatment and is not intended to, nor should be used to, replace professional medical advice. This article may not always be up to date and is not exhaustive of all of the risks and considerations relevant to this particular drug. In no circumstances should this article be relied upon without independent consideration and confirmation by a qualified medical practitioner.
Your doctor will be able to explain all possible uses, dosages, precautions, interactions with other drugs, and other potential adverse effects, and you should always talk to them about any kind of medication you are taking, thinking about taking or wanting to stop taking.