Yeah, when I feel one coming on, I just drink two 6 oz. cups and the next day I have no problem. Weird, but true.
Seem to recall that it lowers the pH of the urine (if you drink enough of it), and that it is bacteriostatic, not bacteriocidal. That is, it will keep the infection from getting worse, not cure it.
This is consistent with my experience. I tried it once when I had a UTI, and I did have relief from the symptoms while I chugged 4-6 glasses/day of the cran. However, that’s a LOT of calories I don’t really need, and the symptoms came back when I stopped. Finally I said “screw it” and went with the Bactrim. Two days, gone forever. So there.
I wonder if this is an extension to humans for something that applies to cats.