There is no correct dosage of cranberry supplements as of 2015, according to WebMD. Some studies have used cranberry supplement capsules of 800 to 1,600 milligrams per day to prevent urinary tract infections, while others used cranberry juice cocktail in daily doses of 10 to 16 ounces.
Cranberries, their juice and extracts are safe, but patients who consume too much develop diarrhea or upset stomach, notes WebMD. During pregnancy, women display these symptoms at lower doses. Before starting on cranberry supplements, patients on any regular drug regimen need to consult their doctor. The supplements interact with medications such as aspirin, blood thinners, some antibiotics, proton pump inhibitors and drugs affecting the liver.