Cranberry supplements are often used to prevent urinary tract infections. Women tend to develop UTIs more frequently than men, because they have a shorter urethra, the tube that leads from the vagina to the bladder. The proximity of the rectum to the urethra also increases the chance of UTIs in women. Cranberry supplements are possibly effective for UTI prevention, MedlinePlus reports, but like nearly all supplements, they do have risks.
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While cranberry tablets may help prevent UTIs, they’re not effective when taken to treat a UTI. At one time, researchers believed that cranberry tablets acidified the urine, making bacteria less likely to survive. Today researchers believe that chemicals in cranberry keep bacteria from sticking to the bladder walls. Once an infection occurs, cranberry tablets will not cure it; antibiotics are required, reports the University of Maryland Medical Center. Delaying antibiotic treatment and trying to cure a UTI with cranberry can result in a more serious kidney infection.
Cranberries contain large amounts of oxalate, a mineral that along with calcium often makes up the most common type of kidney stones. Taking cranberry supplements can raise the oxalate level in the urine by as much as 43 percent, notes MedlinePlus. People who are prone to developing kidney stones or who have high levels of oxalate in their urine should not take cranberry without their medical practitioner’s approval.
Cranberry contains salicylic acid, which is also found in aspirin. People who are allergic to aspirin should not take cranberry supplements without first discussing their use with their medical practitioner, since they may also have an allergy to cranberry.
Cranberry can interfere with the action of several medications, including warfarin, taken to decrease clot formation in the blood. Cranberry may slow the metabolism of warfarin, which makes its effects last longer than normal. This could increase bleeding. An article published in the May-June 2006 issue of “American Journal of Therapeutics” reported that a patient developed severe bleeding after drinking cranberry juice with warfarin. Since cranberry can change the speed at which many drugs are broken down by the liver, talk to your doctor before taking cranberry if you take any other medications, including over-the-counter medications.