Overview
Cranberry (Vaccinium macrocarpon) is an evergreen shrub that grows in bogs in North America. It produces dark red fruits that contain salicylic acid.

Chemicals in cranberries keep bacteria from sticking to the cells in the urinary tract. But they don't seem to be able to remove bacteria that are already stuck to these cells. This might explain why cranberry helps prevent urinary tract infections (UTIs), but doesn't help treat them.

People commonly use cranberry to prevent UTIs. Cranberry is also used for kidney stones, enlarged prostate, the common cold, and many other conditions, but there is no good scientific evidence to support these uses.

Don't confuse cranberry with cramp bark, lingonberry, or uva ursi. These are sometimes also called cranberry but they are not the same.

Uses & Effectiveness 
Possibly Effective for:
Infections of the kidney, bladder, or urethra (urinary tract infections or UTIs). Taking certain cranberry products by mouth seems to help prevent UTIs in adult females, children, and people at risk for developing UTIs due to certain surgeries or radiation treatment. But it doesn't seem to help people with neurogenic bladder, a condition caused by a spinal cord injury. Cranberry products do not seem prevent UTIs in elderly or pregnant people. It's important to note that while cranberry might help prevent UTIs in some people, it shouldn't be used to treat UTIs.

There is interest in using cranberry for a number of other purposes, but there isn't enough reliable information to say whether it might be helpful.

Side Effects
When taken by mouth: Cranberry is commonly consumed in foods. Cranberry juice and cranberry extracts are likely safe for most adults. Drinking too much cranberry juice might cause some side effects such as mild stomach upset and diarrhea in some people.

Special Precautions and Warnings
When taken by mouth: Cranberry is commonly consumed in foods. Cranberry juice and cranberry extracts are likely safe for most adults. Drinking too much cranberry juice might cause some side effects such as mild stomach upset and diarrhea in some people.

Pregnancy and breast-feeding: Cranberry is commonly consumed in foods. There isn't enough reliable information to know if cranberry is safe to use in larger amounts when pregnant or breast-feeding. Stay on the safe side and stick to food amounts.

Children: Cranberry is commonly consumed in foods. There isn't enough reliable information to know if cranberry is safe to use as medicine or what the side effects might be.

Aspirinallergy: Cranberries contain significant amounts of salicylic acid. Salicylic acid is similar to aspirin. Avoid drinking large quantities of cranberry juice if you are allergic to aspirin.

Diabetes: Some cranberry juice products are sweetened with extra sugar. If you have diabetes, stick with cranberry products that are sweetened with artificial sweeteners.

Kidney stones: Cranberry juice and cranberry extracts contain a large amount of a chemical called oxalate. Since oxalate is found in kidney stones, cranberry might increase the risk of kidney stones. If you have a history of kidney stones, stay on the safe side and avoid taking cranberry extract products or drinking a lot of cranberry juice.

Interactions 
Moderate Interaction
Be cautious with this combination

Warfarin (Coumadin) interacts with CRANBERRY
Warfarin is used to slow blood clotting. Cranberry might increase how long warfarin is in the body, and increase the chances of bruising and bleeding. Be sure to have your blood checked regularly. Your warfarin dose might need to be changed.

Atorvastatin (Lipitor) interacts with CRANBERRY
Cranberry might decrease how quickly the body breaks down atorvastatin. This might increase the effects and side effects of atorvastatin. Avoid drinking large amounts of cranberry juice if you are taking atorvastatin.

Medications changed by the liver (Cytochrome P450 2C9 (CYP2C9) substrates) interacts with CRANBERRY

Some medications are changed and broken down by the liver. Cranberry might change how quickly the liver breaks down these medications. This could change the effects and side effects of these medications.

Nifedipine (Procardia) interacts with CRANBERRY
Cranberry might decrease how quickly the body breaks down nifedipine. Drinking cranberry juice while taking nifedipine might increase the effects and side effects of nifedipine.

Minor Interaction
Be watchful with this combination

Medications changed by the liver (Cytochrome P450 2C9 (CYP2C9) substrates) interacts with CRANBERRY
Some medications are changed and broken down by the liver. Cranberry might change how quickly the liver breaks down these medications. This could change the effects and side effects of these medications.

Diclofenac (Voltaren, others) interacts with CRANBERRY
Cranberry might decrease how quickly the body breaks down diclofenac. Drinking cranberry juice while taking diclofenac might increase the effects and side effects of diclofenac.

Dosing
Cranberry is commonly consumed in the diet in juices, jellies, sauces, and other foods.

As medicine, cranberry dried powder has most often been used by adults in doses of 250-1500 mg by mouth daily for up to 6 months. Cranberry extract has most often been used in doses of 120-1600 mg by mouth daily for 12 weeks. And cranberry juice drinks are often used in doses of 120-750 mL daily for up to 90 days. Speak with a healthcare provider to find out what type of product and dose might be best for a specific condition.