Can I take Magnesium and Warfarin together?

Why this happens

Magnesium can bind to warfarin in the digestive tract, which may prevent some of the medication from being absorbed into your bloodstream. Additionally, some forms of magnesium (like magnesium hydroxide) can act as a laxative, speeding up how quickly medicine moves through your system, further reducing absorption.

You may be experiencing an interaction between magnesium and warfarin if:

• You notice changes in your INR results, such as readings outside your usual range.

• You develop unusual bruising or bleeding, including nosebleeds or bleeding gums.

• You feel dizzy, lightheaded, or unusually tired.

• You experience digestive symptoms, such as diarrhoea, which may affect warfarin absorption.

• Symptoms start after starting magnesium supplements or changing the dose.
  

You do not need to stop taking magnesium, but you should separate the doses. Take your magnesium supplement at least 2 hours before or 2 hours after your warfarin dose. Always inform your doctor or anticoagulant clinic if you start or stop any supplements, as they may want to check your INR (blood clotting time) more frequently.

If you have any of the above symptoms, you should:

• Contact your GP or anticoagulation clinic for advice as soon as possible.

• Do not stop taking warfarin suddenly unless advised by a healthcare professional.

• Attend any INR blood tests arranged to monitor your clotting levels.

• Avoid starting, stopping, or changing magnesium supplements without medical advice.

• Tell your healthcare professional about all medicines, supplements, and herbal products you are taking.

Vitamin K intake

Sudden changes in your diet, especially the amount of green leafy vegetables (rich in Vitamin K), can dangerously alter how your medicine works. Keep your intake consistent.

Drug interaction

Magnesium supplements can interfere with how warfarin is absorbed. You must space these medicines at least 2 hours apart to ensure your blood-thinning dose remains effective.

Bleeding risk

You must seek immediate medical attention for signs of internal bleeding, such as unexplained bruising, nosebleeds that do not stop, or red/dark brown urine.

Foods high in Vitamin K (e.g. spinach, kale, broccoli, Brussels sprouts)

Vitamin K helps your blood to clot, which works against warfarin. You do not need to avoid these foods, but you must keep the amount you eat consistent. Sudden changes in your intake can change how your blood clots.

Cranberry juice and cranberry products

Cranberry can increase the effect of warfarin, making your blood too thin and increasing the risk of bleeding. It is best to avoid cranberry juice and supplements entirely while taking warfarin.

Grapefruit juice

Grapefruit juice may increase the effect of warfarin in some people, increasing the risk of bleeding. It is safest to avoid it or keep your intake very small and consistent.

Alcohol

Binge drinking or sudden changes in alcohol consumption can affect how warfarin works. Stick to a consistent, moderate amount within the recommended daily limits.

Pomegranate juice

Some evidence suggests pomegranate juice may interact with warfarin and increase the risk of bleeding. It is best to avoid large amounts.

Dairy products and high-calcium foods

Large amounts of calcium can interfere with how your body absorbs magnesium. If you take a magnesium supplement, try to take it at a different time of day than high-calcium meals or calcium supplements.

Taking multiple medicines? Our Medicines Interaction Checker helps you check whether your prescriptions, over-the-counter medicines, and supplements are safe to take together. Simply search for your medicines to see potential interactions and what to do about them.

Disclaimer

This information is for general educational purposes only and should not be relied upon as a substitute for professional medical advice. Always consult your GP, pharmacist, or another qualified healthcare professional before making decisions about your medications. Individual circumstances may vary, and only a healthcare professional who knows your medical history can provide personalised guidance.