Furosemide

Fluid retention and high blood pressure are conditions that affect many adults in the UK and can place significant strain on the heart and kidneys when left unmanaged. Furosemide tablets are a prescription-only loop diuretic used to remove excess fluid from the body and to support blood pressure control as part of cardiovascular therapy. They are one of the most widely prescribed medicines in the UK for oedema and heart failure. A prescription can only be issued following a clinical consultation.

Furosemide tablets are an oral prescription medicine containing furosemide as the active ingredient. Furosemide belongs to the loop diuretic class of medicines, so called because they act on a specific part of the kidney called the loop of Henle. Diuretics are sometimes referred to informally as water tablets.

Furosemide is licensed in the UK for several indications. These include oedema (fluid retention) associated with heart failure, liver cirrhosis, and kidney disease. It is also used in the treatment of hypertension, often alongside other antihypertensive medicines, where its diuretic effect supports blood pressure control. In hospital settings, furosemide may be used for additional indications under specialist supervision; this page covers only the standard oral tablet indications as reflected in the current SmPC.

Furosemide is available as a generic medicine from multiple manufacturers. The 20 mg and 40 mg tablet strengths are available through this service. Because furosemide acts relatively quickly and potently, it requires regular monitoring of kidney function, fluid balance, and electrolytes during treatment. Your prescriber will advise on the appropriate monitoring schedule for your situation.

Important: Furosemide requires ongoing clinical monitoring. Regular blood tests to check kidney function, electrolytes (particularly potassium and sodium), and fluid balance are an essential part of safe treatment. Your prescriber will determine the appropriate monitoring schedule for you. Online prescribing of furosemide is only appropriate where an adequate clinical history is available and where regular monitoring can be ensured. Your prescriber will assess this as part of the consultation.

Furosemide works by acting directly on the kidneys to increase the amount of urine the body produces, thereby reducing excess fluid and supporting fluid balance throughout the body.

Action on the Loop of Henle

Inside the kidney, filtrate passes through a structure called the loop of Henle, where sodium, potassium, and chloride are normally reabsorbed back into the body. Furosemide blocks the sodium-potassium-chloride co-transporter in the thick ascending limb of the loop of Henle. By blocking this transporter, furosemide prevents the reabsorption of these electrolytes. Water follows the electrolytes out of the body in urine, resulting in a marked increase in urine output.

Effects on Blood Pressure and Fluid Retention

The removal of excess sodium and water reduces the overall volume of fluid circulating in the blood vessels. This lowers the pressure within the blood vessels and reduces the strain on the heart. In oedema, the removal of excess fluid from the tissues relieves swelling, breathlessness, and discomfort. This combination of effects makes furosemide a key medicine in cardiovascular therapy for patients with heart failure, kidney disease, and conditions causing significant fluid retention.

Because furosemide can remove large amounts of fluid and electrolytes quickly, it is important to take it exactly as prescribed and to attend any monitoring appointments arranged by your prescriber.

Always take furosemide exactly as your prescriber instructs. The information below summarises key points from the current UK SmPC. Read the Patient Information Leaflet supplied with your medicine before starting treatment.

• Take furosemide once or twice daily as directed by your prescriber. If you take it once daily, take it in the morning. If you take it twice daily, take the second dose no later than mid-afternoon. Taking furosemide late in the day increases the likelihood of needing to pass urine during the night.
• Furosemide can be taken with or without food.
• Swallow the tablet with a glass of water.
• If you miss a dose, take it as soon as you remember on the same day. If you only remember the following day, skip the missed dose and continue with your normal schedule. Do not take two doses on the same day.
• Do not stop taking furosemide without speaking to your prescriber first. Stopping suddenly can cause fluid to accumulate rapidly, which can worsen breathlessness and swelling.
• Attend all blood test appointments arranged by your prescriber. Furosemide affects potassium, sodium, and kidney function, and these need to be monitored regularly throughout treatment.
• Furosemide can cause you to pass urine more frequently, particularly in the first few hours after taking the tablet. Plan your daily activities with this in mind, especially if you are starting treatment or your dose has recently been increased.

Furosemide tablets are available in two strengths through this service. The appropriate strength and dosing frequency will be determined by your prescriber based on the condition being treated, your kidney function, and your clinical response to treatment.

Furosemide 20 mg Tablets

The 20 mg tablet is typically used as a starting dose in mild to moderate oedema or in patients who may be more sensitive to the effects of diuretic therapy, such as older patients or those with mild kidney impairment. Starting at a lower dose allows the prescriber to assess tolerability and fluid balance response before any increase is considered.

Furosemide 40 mg Tablets

The 40 mg tablet is the most commonly prescribed dose for adults with oedema associated with heart failure, liver disease, or kidney disease. For hypertension, furosemide may be prescribed at 40 mg once daily, though it is less commonly used as a first-line antihypertensive than other diuretic classes. The 40 mg dose may be taken once or twice daily depending on the clinical situation.

For resistant oedema or in patients requiring more intensive diuretic therapy, the dose may be increased beyond 40 mg. Doses above 80 mg per day are generally used only under specialist supervision and are outside the scope of standard online prescribing. All dose decisions are made by your prescriber. Do not adjust your dose without medical advice.

Like all medicines, furosemide can cause side effects, although not everyone experiences them. The information below is based on the current UK SmPC. Refer to the Patient Information Leaflet for the full list.

Common Side Effects (may affect up to 1 in 10 people)

• Increased frequency of passing urine, particularly in the first few hours after taking the tablet. This is an expected effect of the medicine.
• Low blood pressure, particularly when standing up quickly (postural hypotension), which may cause dizziness or lightheadedness
• Electrolyte disturbances, including low potassium (hypokalaemia), low sodium (hyponatraemia), and low magnesium. These can cause muscle cramps, weakness, or an irregular heartbeat. Regular blood tests help to detect and manage these changes.
• Thirst and dry mouth due to fluid loss
• Raised blood uric acid levels, which may trigger or worsen gout in susceptible patients

Uncommon Side Effects (may affect up to 1 in 100 people)

• Nausea, vomiting, or diarrhoea
• Raised blood glucose levels, which may be relevant for patients with or at risk of diabetes
• Skin rash or itching
• Raised blood cholesterol or triglyceride levels with longer-term use

Serious Side Effects: Seek Urgent Medical Attention

Contact your prescriber or go to your nearest accident and emergency department promptly if you experience any of the following:

• Signs of severe electrolyte disturbance such as muscle weakness, cramps, confusion, or an irregular heartbeat
• Significant reduction in urine output, which may indicate worsening kidney function
• Signs of severe dehydration such as extreme thirst, very dark urine, dizziness, and confusion
• Signs of a serious allergic reaction such as sudden swelling of the face, lips, tongue, or throat, difficulty breathing, or a severe skin reaction
• Hearing problems or ringing in the ears (tinnitus), which is a rare side effect associated with high doses or rapid intravenous administration, but should be reported promptly if it occurs with oral treatment

Report any suspected side effect to your prescriber, pharmacist, or via the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk.

Furosemide Tablets May Be Suitable If You:

• Are an adult with a confirmed diagnosis of oedema associated with heart failure, liver cirrhosis, or kidney disease
• Have hypertension and have been assessed as requiring diuretic therapy as part of your treatment plan
• Are already prescribed furosemide and require a repeat prescription through an online prescribing service, with adequate recent monitoring results available

Furosemide Tablets Are Not Suitable If You:

• Are anuric (producing no urine) or have severe kidney failure where diuretic therapy is contraindicated
• Have severely low potassium or sodium levels that have not been corrected
• Have severe liver disease with hepatic coma or pre-coma
• Have Addison's disease (adrenal insufficiency)
• Are dehydrated or have significant reduction in circulating blood volume
• Are pregnant. Furosemide should not routinely be used during pregnancy. Your prescriber will assess whether it is appropriate in your specific circumstances.
• Are breastfeeding, as furosemide passes into breast milk
• Have a known allergy or hypersensitivity to furosemide, sulfonamides, or any excipient listed in the SmPC
• Are under 18 years of age (this service is for adults only)

Furosemide interacts with a number of commonly prescribed medicines. Tell your prescriber about all medicines you take, including over-the-counter products and herbal supplements. The following interactions are of particular clinical importance:

• ACE inhibitors and angiotensin receptor blockers (ARBs): combining these with furosemide can cause a significant fall in blood pressure, particularly with the first dose. Your prescriber will manage this carefully.
• Other antihypertensive medicines: the blood pressure-lowering effect of furosemide may be enhanced when taken with other medicines in this class.
• NSAIDs such as ibuprofen: these can reduce the diuretic effect of furosemide and increase the risk of kidney problems. Avoid regular use of NSAIDs while taking furosemide.
• Digoxin: electrolyte disturbances caused by furosemide, particularly low potassium, can increase the risk of digoxin toxicity. Electrolyte monitoring is especially important in patients taking both medicines.
• Lithium: furosemide can increase lithium levels, raising the risk of toxicity. Close monitoring is required.
• Aminoglycoside antibiotics such as gentamicin: concurrent use may increase the risk of hearing damage and kidney toxicity.

This is not a complete list of interactions. Your prescriber will carry out a full clinical assessment, including a review of your current medicines, before any prescription is considered.

Furosemide is a Prescription Only Medicine that requires ongoing clinical monitoring. The clinical consultation is the essential first step. A prescription will only be issued if a registered prescriber determines, based on their individual assessment of your circumstances, that furosemide is clinically appropriate for you.

During your online consultation with Pharmacy Planet, a registered prescriber will review your clinical information. This includes your diagnosis, current fluid balance status, kidney function results, electrolyte levels, other medicines, and any other relevant medical history. Because furosemide requires regular monitoring, the prescriber will also assess whether adequate monitoring is in place for you before considering whether to issue a prescription.

Not all consultations will result in a prescription being issued. The prescriber may request recent blood test results, suggest an alternative approach, or recommend a different dose. This process is designed to ensure your safety.

If you are being managed for heart failure, oedema, or hypertension by your GP or a hospital team, please keep them informed of all medicines you are taking, including any prescribed through online services. Safe use of furosemide depends on coordinated care and regular clinical oversight.

• Store below 25°C.
• Store in the original packaging to protect from light and moisture.
• Keep out of the sight and reach of children.
• Do not use after the expiry date printed on the packaging.
• Do not dispose of medicines via household waste or wastewater. Return unused or out-of-date tablets to your pharmacist for safe disposal.
• Full storage instructions are provided in the Patient Information Leaflet supplied with your medicine.

The table below compares diuretic tablets available at Pharmacy Planet. Diuretics lower blood pressure and reduce fluid retention by increasing urine production. Different classes of diuretic work at different sites in the kidney.

Important: This comparison is for general information only and does not replace medical advice. A prescriber will decide which treatment is suitable for you following an online consultation.

Pharmacy Planet is a GPhC-registered online pharmacy providing prescription medicines through a clinically led consultation process. Our registered prescribers and pharmacists are committed to patient safety, responsible prescribing, and accurate patient information.

For medicines such as furosemide that require ongoing monitoring, our prescribers take particular care to ensure that appropriate clinical oversight is in place before any prescription is issued. We follow GPhC standards, MHRA guidance, and ASA advertising regulations in all aspects of our service.

Our pharmacy team is available to answer questions about furosemide, diuretic therapy, or cardiovascular management more broadly. We are committed to providing clear, honest information to support you in managing your health safely and with confidence.

References

1. Electronic Medicines Compendium (eMC). Furosemide 20 mg and 40 mg tablets — Summary of Product Characteristics. https://www.medicines.org.uk/emc. Accessed May 2026.
2. National Institute for Health and Care Excellence (NICE). Chronic heart failure in adults: diagnosis and management. NICE guideline NG106. https://www.nice.org.uk/guidance/ng106. Accessed May 2026.
3. NHS. Furosemide. https://www.nhs.uk/medicines/furosemide. Accessed May 2026.
4. Joint Formulary Committee. British National Formulary (BNF). Furosemide. BMJ Group and Pharmaceutical Press. https://bnf.nice.org.uk. Accessed May 2026.
5. Medicines and Healthcare products Regulatory Agency (MHRA). Yellow Card — report a side effect. https://yellowcard.mhra.gov.uk. Accessed May 2026.