The evidence on cranberries to prevent urinary tract infections

Cranberries are often used to prevent urinary tract infections (UTIs).

Is it worth the effort?

Here’s a small study that concludes it is.

  • 12 women with a history of UTIs participated in this 12-week study and were then followed for 2 years.
  • The daily doses were 7.5 grams of cranberry concentrate in 50 mL of water (about a shotglassful), or 750 mL of juice (about the size of a wine bottle), or two tablets of concentrate.
  • During the study none of the women had a UTI, and no side effects were reported.
  • 2 years later, 8 of the women who continued to take cranberry were free from UTIs.

The results in this study are better than generally reported. One review concluded that on average 100 women would have to be treated for one year in order to prevent at least 1 urinary tract infection in 15 to 33 women.

The Cochrane Review adds that it’s not clear if cranberries are effective to prevent UTIs in children, or in elderly men and women. Furthermore, the high numbers of dropouts from studies of cranberry juice suggest it might not be acceptable over long periods of time.

2/20/07 20:36 JR

Hi, I’m JR

John Russo, Jr., PharmD, is president of The MedCom Resource, Inc. Previously, he was senior vice president of medical communications at, a complementary and alternative medicine website.