Can I take Magnesium and Warfarin together?

You should take magnesium at least 2 hours before or 2 hours after taking warfarin as it may slightly reduce how well warfarin works and can increase the risk of blood clots.

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.

How to know if you're having a drug interaction

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.
  

What you should do

You do not need to stop taking magnesium, but you should separate the doses. 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.

Important precautions

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

Warfarin significantly increases your risk of serious bleeding. You must seek immediate medical help if you have a fall, a head injury, or notice signs of internal bleeding such as black stools or coughing up blood.

Pregnancy

Warfarin can cause serious harm to an unborn baby. You must use effective contraception while taking it and inform your doctor immediately if you think you are pregnant.

Kidney disease

If you have severe kidney problems, your body may not be able to remove excess magnesium, leading to dangerously high levels in the blood. Check with your doctor before use.

Food and drink warnings

Alcohol

It is best to avoid or strictly limit alcohol while taking warfarin. Alcohol can affect how your liver processes the medicine, making your blood too thin and increasing the risk of dangerous bleeding.

It is best to avoid or strictly limit alcohol when taking magnesium. Alcohol acts as a diuretic, which can increase the amount of magnesium your body loses through urine, potentially making the supplement less effective. Additionally, chronic alcohol use can lead to magnesium deficiency.

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.

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.

Caffeine (Coffee, Tea, Energy drinks)

It is best to limit caffeine intake around the time you take magnesium. Like alcohol, caffeine has a mild diuretic effect and can increase the excretion of magnesium through the kidneys.

Using other medicines

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.