Cranberry may increase the anticoagulant effect from blood thinners like warfarin and lead to bruising or bleeding.

If you take an oral blood thinner, check with your doctor before consuming large amounts of cranberry or cranberry juice. You may need to have your International Normalized Ratio (INR) or other blood clotting lab test checked more frequently, or have your warfarin (Jantoven) dose changed.

Call your doctor right away if you have signs of an interaction such as unusual bleeding or bruising, vomiting, blood in your urine or stools, headache, dizziness, or weakness.

In one case report in a kidney transplant patient, lower tacrolimus blood levels were reported when used with cranberry juice extract. Levels returned to normal when cranberry cranberry juice extract was stopped.

It is important to tell your doctor about all the medications you use, including prescription, over-the-counter (OTC) medicines, vitamins and herbal supplements. Do not stop using any medications without first talking to your doctor.

Learn more: Drug interactions with cranberry (in more detail)

Does cranberry work for a UTI?

Some people drink cranberry juice to help prevent urinary tract infections (UTI).

• Although data are conflicting, some studies suggest cranberry can reduce recurrent UTIs some patients, but it is not likely to be helpful in curing an established UTI.
• However, increasing fluid intake in general (such as water) can help reduce the risk of a UTI recurrence. Some clinicians recommend a daily target of 2 to 3 liters of fluid per day. If you have recurrent UTIs, contact your doctor for further advice.
• A UTI can worsen to a kidney or blood infection so it important to see your doctor to determine if you need an antibiotic.

Cranberries are thought to be helpful for UTIs as they contain proanthocyanidins and fructose, agents that may stop the bacteria being able to attach to cell walls in the urinary system.

Drinking cranberry juice is probably not harmful, but it can be high in calories and sugar, and may cause heartburn, diarrhea or weight gain in some people. Cranberry products may also promote kidney stone formation by increasing urine oxalate excretion.

This is not all the information you need to know about cranberry drug interactions for safe and effective use and does not take the place of your doctor’s directions. Review the full cranberry information and discuss this information and any questions you have with your doctor or other health care provider.