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Warfarin: what to be careful with
Warfarin thins the blood by blocking the vitamin K-dependent clotting factors, and is used to prevent and treat blood clots.
General information only, and not exhaustive. This is not medical advice, not a full list of interactions, and not a reason to start, stop or change a medicine. Interactions depend on the exact drug, the dose, your other medicines and your own health — a pharmacist or doctor is the one who decides. Always read the leaflet that came with your medicine, and ask your pharmacist before adding anything, including supplements.
Group, not a brandATC B01AA
Examples in this group: warfarin, phenprocoumon, acenocoumarol (vitamin K antagonists). Interactions usually belong to the whole group, but your own leaflet is brand-specific — always the final word.
Food and drink to be careful with
- Vitamin K — consistency, not avoidance. This is the point most often got wrong. Green leafy vegetables, broccoli, Brussels sprouts and some oils are rich in vitamin K, which opposes warfarin. The guidance is not to avoid them: it is to eat a steady amount, because the dose was set against your usual diet. A sudden salad phase, or a sudden stop, moves the INR.
- Cranberry juice. Repeatedly associated with a raised INR and named in warfarin leaflets. Large or new intakes are the concern.
- Grapefruit and pomelo. Can raise warfarin levels through the same enzyme route as with statins.
- Supplements. St John's wort lowers warfarin's effect; several others — including high-dose fish oil, ginkgo, garlic and ginger preparations — are discussed as adding bleeding risk. Any new supplement is worth raising before starting it, not after.
Timing around meals
Warfarin is normally taken once a day at the same time, most often in the evening so that a dose change after an INR result can be made the same day. Food does not need to be avoided; consistency of vitamin K intake is what counts.
Alcohol
Binge drinking is the clear risk: it can raise INR acutely, and it adds fall and bleeding risk. Steady, modest intake is handled more predictably, and long-term heavy drinking with liver damage changes everything about warfarin control.
Other things to watch
- Many antibiotics raise the INR, sometimes sharply; an INR check is common when a course is prescribed.
- NSAIDs, including over-the-counter ibuprofen, add bleeding risk on top of warfarin.
- Any unusual bruising, bleeding gums, blood in urine or stool, or a fall with a head impact is a same-day medical matter, not something to watch and see.
If anything here does not match what you were told, or you notice a new symptom after starting a medicine, contact your pharmacist or doctor — do not just stop taking it. Stopping some medicines suddenly is more dangerous than any food interaction.
Source: The product's own Summary of Product Characteristics and patient information leaflet, published per medicine by the licensing authority. Anticoagulant clinics also issue their own written vitamin K and alcohol guidance, which takes precedence for the person it was given to. · checked 2026-09-02
Frequently asked questions
What should I avoid with warfarin?
Vitamin K — consistency, not avoidance is the one people ask about most: This is the point most often got wrong. Green leafy vegetables, broccoli, Brussels sprouts and some oils are rich in vitamin K, which opposes warfarin. The guidance is not to avoid them: it is to eat a steady amount, because the dose was set against your usual diet. A sudden salad phase, or a sudden stop, moves the INR. This is general information — your leaflet and pharmacist have the specifics.
Can I drink alcohol with warfarin?
Binge drinking is the clear risk: it can raise INR acutely, and it adds fall and bleeding risk. Steady, modest intake is handled more predictably, and long-term heavy drinking with liver damage changes everything about warfarin control.
Should warfarin be taken with food?
Warfarin is normally taken once a day at the same time, most often in the evening so that a dose change after an INR result can be made the same day. Food does not need to be avoided; consistency of vitamin K intake is what counts.
Other medicine groups
Statins
Statins lower LDL cholesterol by slowing the liver's own cholesterol production, and are prescribed to reduce the long-term risk of heart attack and stroke.
Metformin
Metformin lowers blood glucose mainly by reducing the amount of glucose the liver releases, and is usually the first medicine used in type 2 diabetes.
Levothyroxine
Levothyroxine replaces the thyroid hormone the body is not making enough of, in an underactive thyroid.
DOACs (direct oral anticoagulants)
DOACs thin the blood by directly blocking a single clotting factor, and are used to prevent stroke in atrial fibrillation and to treat and prevent venous clots.
SSRIs and SNRIs
These antidepressants raise the availability of serotonin (and for SNRIs also noradrenaline) in the brain, and are used for depression and several anxiety conditions.
NSAIDs
NSAIDs reduce pain, fever and inflammation by blocking prostaglandin production.
All medicine groups · Alcohol units and clearance · Blood test reference ranges
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