Warfarin Shortage UK — Current Supply Status & Patient Guide

Last reviewed: 13 May 2026 Next review due: When DHSC or NHS England issues a new supply notification for warfarin Database last checked: 13 May 2026

MediWatch Trust Signals

• Evidence score: 88/100 — All clinical claims sourced from NHS, eMC PIL/SmPC, SPS, or MHRA
• Trust score: 90/100 — Official UK sources only; weak history/manufacturing claims removed or genericised
• Reviewed for source alignment: 13 May 2026
• Source trail: NHS Medicines A-Z, NHS Specialist Pharmacy Service, electronic Medicines Compendium, MHRA, Bumps
• MediWatch page status: Source-backed clinical content

Current UK Shortage Status

There is no current national shortage signal for warfarin in the MediWatch live database. We monitor DHSC medicine supply notifications, NHS England alerts, and Community Pharmacy England bulletins twice daily, and no active shortage row is recorded for this medicine at the time of writing.

This does not guarantee that every pharmacy will have every strength in stock on every day. Local supply varies by wholesaler and dispensing volumes. If one pharmacy cannot supply your prescription, another branch or supplier may be able to.

What to do today:

• Do not skip doses or change your dose because of a supply concern.
• If your usual pharmacy cannot dispense your warfarin, ask them to check alternative suppliers or branches.
• Contact your GP practice or anticoagulation clinic if you are unable to obtain your medicine.
• Sign up for MediWatch alerts and we will notify you immediately if a national shortage is declared.

Plain-English Summary

Warfarin is an anticoagulant — sometimes called a "blood thinner," although it does not actually make your blood thinner. It is used to treat and prevent blood clots. Because it has a narrow therapeutic window, it requires regular blood tests (INR checks) and careful monitoring of diet, other medicines, and illness. If you take warfarin, you should carry an anticoagulant alert card at all times.

What Warfarin Is Used For

Your doctor may prescribe warfarin if you have:

• a deep vein thrombosis (DVT) or pulmonary embolism (PE)
• an irregular heartbeat called atrial fibrillation
• a mechanical (artificial) heart valve
• a blood clotting disorder
• had a transient ischaemic attack (TIA)

For many of these conditions, warfarin treatment is long term. Your doctor will explain why you need it and how long you are likely to take it. Always follow the dose instructions on your treatment record or anticoagulant booklet. If you are unsure, ask your pharmacist, GP, or anticoagulation clinic — do not guess.

How Warfarin Works

Warfarin is a vitamin K antagonist. It works by blocking an enzyme your body needs to recycle vitamin K. Without active vitamin K, your liver produces fewer clotting factors, which reduces your blood's ability to form clots. The full anticoagulant effect builds over several days as existing clotting factors clear from your bloodstream.

If rapid anticoagulation is needed, a clinician may use heparin injections alongside warfarin for the first few days. This is a clinical decision — do not start or stop any injection treatment on your own.

Warfarin has a narrow therapeutic window. Too little and clots can form; too much and bleeding risk rises sharply. This is why regular blood testing is essential.

Forms and Strengths Available in the UK

In the UK, warfarin is available as:

• Tablets — 0.5 mg, 1 mg, 3 mg, and 5 mg
• Oral suspension — 1 mg/1 ml (for people who cannot swallow tablets)

The tablets are scored and can be divided into equal halves if a pharmacist or prescriber advises this. The different strengths are different colours to help identification:

• 0.5 mg — white
• 1 mg — brown
• 3 mg — blue
• 5 mg — pink

Your anticoagulation clinic or pharmacist can show you how to identify your dose if you are unsure. Keep tablets in the original packaging to protect them from light. Do not use after the expiry date.

Brand and Generic Names

The active ingredient is warfarin sodium. It is prescribed generically in most of the UK. One brand name you may see is Marevan (ADVANZ Pharma).

Other UK marketing authorisation holders listed on the electronic medicines compendium (eMC) include Ranbaxy (UK) Limited (a Sun Pharmaceutical Company), Rosemont Pharmaceuticals Limited, and Strides Pharma UK Ltd. Your pharmacy may supply warfarin from any of these manufacturers depending on stock.

If your supply looks different (colour, shape, or packaging), check with your pharmacist that it is the correct strength. Do not assume a different colour means a wrong medicine.

Invention and Approval History

Warfarin belongs to a class of medicines called vitamin K antagonists. It was developed following research into compounds that affect blood clotting and has been used as an oral anticoagulant for many decades. It remains one of the most widely studied anticoagulants and is listed on the World Health Organization's List of Essential Medicines.

Specific development dates, early research institutions, and regulatory approval timelines are drawn from widely cited historical literature; for detailed chronology, consult a peer-reviewed history of anticoagulation or the British Pharmacopoeia.

How Medicines of This Type Are Made

Warfarin sodium is manufactured as an active pharmaceutical ingredient and formulated into licensed tablets or oral liquid under medicines manufacturing regulations. The finished products contain excipients such as lactose, starch, and magnesium stearate, with colouring agents added to help distinguish strengths. Different manufacturers hold marketing authorisations for warfarin products in the UK. Specific production site information is held by the marketing authorisation holder and regulated by the MHRA.

UK Suppliers and Marketing Authorisation Holders

Based on the electronic medicines compendium (eMC) search results, warfarin products currently listed for the UK market include marketing authorisation holders:

• ADVANZ Pharma — Marevan and generic warfarin tablets
• Ranbaxy (UK) Limited (a Sun Pharmaceutical Company) — warfarin tablets
• Rosemont Pharmaceuticals Limited — warfarin sodium 1 mg/1 ml oral suspension
• Strides Pharma UK Ltd — warfarin 5 mg tablets

This list reflects products with active eMC entries at the time of writing. It is not exhaustive, and manufacturers may change. If you are concerned about the source of your supply, ask your pharmacist which MAH's product you have received.

Common Side Effects

The main side effect of warfarin is an increased risk of bleeding. You may notice:

• nosebleeds that take longer to stop
• bleeding gums
• bruising more easily than usual
• heavier periods

Not everyone gets side effects. Some people take warfarin for years without problems. The risk of bleeding is closely linked to how high your INR is, which is why monitoring matters.

Other possible side effects include:

• skin rashes
• hair loss
• diarrhoea
• purple discolouration or bruising of the skin
• yellowing of the skin or eyes (jaundice)

For a full list, read the patient information leaflet that comes with your medicine or search for your specific product on the eMC website.

Report side effects: You can report side effects to the MHRA using the Yellow Card scheme.

Serious Side Effects and Urgent Help

Warfarin can cause serious bleeding. Use NHS 111, A&E or 999 based on the severity and type of symptom.

Call NHS 111 now for urgent advice if you have:

• bleeding that is not heavy but will not stop, or stops and starts again
• pink, red or brown urine
• black poo
• bruises for no clear reason, larger than expected, or getting bigger
• sudden severe back pain
• increased vaginal bleeding, bleeding between periods, or bleeding after the menopause
• taken more warfarin than prescribed
• had a head injury, even a minor bump, while taking warfarin

Go to A&E now if you have:

• a nosebleed you cannot stop that lasts longer than 10 minutes
• blood in your vomit
• blood when you cough

Call 999 now if you have:

• a sudden, severe headache
• a seizure or fit
• sudden loss of vision or blurred vision
• numbness or tingling in your arms or legs
• slurred speech
• cannot be woken up or lose consciousness
• difficulty breathing, breathing faster than usual, or chest pain
• heavy bleeding where blood is spraying, pouring, or enough to make a puddle
• signs of a severe allergic reaction, such as swelling of the lips, mouth, throat or tongue, severe breathing difficulty, blue/grey/pale lips or skin, sudden confusion, collapse, or fainting that does not resolve

Do not drive yourself to A&E. Follow the advice from NHS 111, 999, your anticoagulation clinic, GP, or pharmacist.

A rare but serious condition called calciphylaxis (vascular calcification with skin necrosis) has been reported in people taking warfarin, particularly those with chronic kidney disease. Seek urgent medical advice if you develop a painful skin rash.

Source: NHS — Side effects of warfarin

Interactions and Cautions

Warfarin interacts with many medicines, supplements, and some foods. Always tell your doctor, pharmacist, and anticoagulation clinic about anything new you take — including over-the-counter painkillers, herbal remedies, and vitamins.

Medicines that can interact with warfarin

• Non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen and aspirin — increase bleeding risk
• Antibiotics — many can raise or lower INR unpredictably
• Antidepressants — some interact with warfarin
• Medicines for heart problems such as amiodarone, quinidine, and propafenone
• Medicines for fungal infections such as fluconazole and miconazole
• Medicines for stomach ulcers or acid reflux such as cimetidine, omeprazole, and sucralfate
• Statins and other cholesterol-lowering medicines
• St John's wort — can reduce warfarin's effect
• Vitamin K supplements — can reduce warfarin's effect
• Tramadol — the MHRA issued a safety update warning that tramadol can increase INR and raise the risk of major bruising and bleeding when taken with warfarin

Do not start any new medicine without checking with a healthcare professional first.

Food, drink, and dietary supplements

• Alcohol: Do not drink large amounts. Binge drinking or sudden increases can dangerously raise INR.
• Cranberry juice and cranberry products: Avoid them while taking warfarin. They can increase warfarin's effect and bleeding risk.
• Grapefruit juice: Avoid it. It can interact with many medicines, including warfarin.
• Vitamin K-rich foods: Broccoli, spinach, kale, and other green leafy vegetables contain vitamin K, which opposes warfarin. You do not need to avoid them completely, but keep your intake consistent and talk to your warfarin clinic before making big dietary changes.

Other cautions

• Smoking and stopping smoking: Both can affect INR. Tell your clinic if you start or stop smoking.
• Weight changes: Losing or gaining significant weight can change the dose you need.
• Intercurrent illness: Vomiting, diarrhoea, fever, or infections can affect INR. You may need an extra blood test.

Pregnancy, Breastfeeding, Driving, Alcohol and Kidney/Liver Cautions

Pregnancy

Warfarin is not usually used during pregnancy because it can affect the baby's development, especially in the first and third trimesters. However, it is sometimes used in specific situations when a doctor judges the benefits outweigh the risks.

Tell your doctor straight away if you are pregnant or planning to become pregnant. Do not stop taking warfarin unless your doctor tells you to — stopping suddenly can increase your own clotting risk.

For more information, see the Bumps (Best Use of Medicines in Pregnancy) website.

Breastfeeding

Warfarin can be taken while breastfeeding. It is rare for a breastfed baby to experience side effects, but speak to a healthcare professional or call NHS 111 if your baby has unexplained bruises or blood in their urine, poo, or vomit.

Driving and machinery

Warfarin does not usually affect your ability to drive, ride a bike, or use machinery. However, if you feel dizzy, unwell, or have any signs of bleeding, do not drive and seek medical advice.

Alcohol

Avoid drinking large amounts of alcohol while taking warfarin. Alcohol can interact with warfarin and increase bleeding risk. If you drink regularly, tell your anticoagulation clinic so they can factor this into your monitoring.

Kidney and liver cautions

Warfarin should be used with caution if you have liver or kidney problems. Severe liver disease reduces your ability to make clotting factors, while kidney disease increases bleeding risk. Your doctor should check your liver function and kidney function before starting warfarin and monitor you more closely if these organs are impaired.

Missed Doses and Stopping Warfarin

If you miss a dose

• Take it as soon as you remember.
• If you do not remember until the next day, skip the missed dose and take that day's dose as usual.
• Do not take 2 doses to make up for a missed dose.
• Make a note of any missed doses.
• If you often miss doses, or if you miss more than one dose in a row, contact your warfarin clinic for advice.

If you take too much

Taking an extra dose can be dangerous. Contact NHS 111 if you have taken more than your prescribed dose.

Stopping warfarin

Do not stop taking warfarin unless your doctor tells you to. Stopping suddenly can increase your risk of blood clots, which can lead to stroke, heart attack, or pulmonary embolism. If you have concerns about side effects or supply, speak to your GP or anticoagulation clinic before making any changes.

Monitoring Requirements

While you take warfarin, you need regular blood tests to measure your international normalised ratio (INR). This shows how long your blood takes to clot.

• Target INR: For most people, the target range is 2.0 to 3.0. Some people with high-risk mechanical heart valves may need a higher target. Your clinic will tell you your personal target.
• When starting: You will need an INR test every day or every few days until your result is stable in the target range.
• Once stable: Testing usually drops to every 12 weeks.
• More frequent testing: You may need tests every 1–2 weeks if you are high risk, have poor control, start a new medicine, or have an illness.

You will be given an anticoagulant alert card and usually a yellow booklet to record your results and doses. Always carry the alert card and show it to any doctor, dentist, or healthcare professional before you have a procedure. Some people may be trained to self-test their INR at home using a portable monitor.

What affects your INR

Many things can push your INR above or below target:

• missed or changed doses
• new medicines or stopped medicines
• changes in alcohol intake
• changes in smoking status
• significant diet changes
• weight changes
• illness

If your INR is too low, your clotting risk rises. If it is too high, your bleeding risk rises. Your clinic will advise you on dose adjustments. Never change your dose on your own.

What to Ask a Pharmacist or GP During Supply Issues

If your pharmacy cannot supply warfarin, the table below shows who to contact and what they can do.

Never borrow warfarin from someone else, split tablets to stretch supply, or stop taking it without medical advice. Any change to the strength or formulation you take must be confirmed by your pharmacist, prescriber, or anticoagulation clinic.

Related Medicines Your Clinician May Discuss

Warfarin has been used for decades, but newer medicines called direct oral anticoagulants (DOACs) are now commonly prescribed in the UK. These include:

• Apixaban (Eliquis)
• Rivaroxaban (Xarelto)
• Dabigatran (Pradaxa)
• Edoxaban (Lixiana)

DOACs do not require regular INR blood tests and have fewer food and drug interactions. However, they are not suitable for everyone — for example, people with mechanical heart valves or certain types of kidney disease may still need warfarin. There is also an anticoagulant called heparin that is given by injection.

Do not switch from warfarin to a DOAC on your own. This is a prescriber decision based on your condition, kidney function, bleeding risk, and other factors. If you are interested in alternatives, ask your GP or specialist whether a DOAC is appropriate for you.

Frequently Asked Questions

Is warfarin currently in shortage in the UK?

There is no current national shortage signal for warfarin in the MediWatch database. However, local pharmacy stock can vary. If your pharmacy cannot supply it, ask them to check other branches or suppliers, and contact your anticoagulation clinic if you cannot obtain your medicine.

What should I do if my pharmacy cannot get warfarin?

Do not skip doses or change your dose. Ask your pharmacist to check alternative suppliers or branches. If you still cannot obtain it, contact your GP or anticoagulation clinic for advice.

Can my pharmacist give me a different strength if my usual one is out of stock?

Only your prescriber or anticoagulation clinic can confirm whether a different combination of licensed strengths is appropriate for you. Your pharmacist may be able to check what is available, but do not change your dose or tablet combination without clinical advice.

Does it matter if my warfarin brand changes?

Some patients notice small changes in control when switched between manufacturers. If you have concerns after a brand change, tell your anticoagulation clinic. Always check with your pharmacist that any new supply is the correct strength.

How often do I need an INR blood test?

When starting warfarin, you may need tests daily or every few days until stable. Once stable, testing is usually every 12 weeks. You may need more frequent tests if you start new medicines, are ill, or have poor control.

Official Sources and How to Report a Problem

• NHS Medicines A-Z — Warfarin: https://www.nhs.uk/medicines/warfarin/
• NHS Medicines A-Z — Anticoagulants: https://www.nhs.uk/medicines/anticoagulants/
• NHS SPS — Warfarin Monitoring: https://www.sps.nhs.uk/monitorings/warfarin-monitoring/
• Electronic Medicines Compendium (eMC): https://www.medicines.org.uk/emc/search?q=Warfarin
• MHRA Yellow Card (report side effects): https://yellowcard.mhra.gov.uk/
• MHRA Drug Safety Updates: https://www.gov.uk/drug-safety-update
• Bumps (medicines in pregnancy): https://www.medicinesinpregnancy.org/leaflets-a-z/warfarin/
• DHSC Medicine Supply Notifications: https://www.gov.uk/government/publications/medicines-supply-notifications

Report an accuracy issue: If you spot an error or out-of-date information on this page, please contact MediWatch or email hello@mediwatch.co.uk.

*MediWatch is a medicine shortage monitoring service. We are not a substitute for medical advice, diagnosis, or treatment. Always speak to a pharmacist, GP, or specialist for personal medical guidance.*