On the recommendation of an RN on this site, I purchased D-Mannose (a supplement that is a simple sugar) for my MIL to take on a maintenance basis to deal with her almost monthly UTIs. She has not had an infection since starting it last September. I don't take supplements because they are not scientifically proven and you basically pee them all out. But this supplement is otherwise harmless and she had nothing to lose.
nausea,
vomiting,
upset stomach,
diarrhea,
rust-colored or brownish urine,
vaginal itching or discharge,
headaches, and.
gas.
For these reasons, I personally would not take it. If anything says "will cause upset stomach" it "will" upset my stomach.
I had my Mom on cranberry tablets (no juice) and a probiotic. When she passed, she hadn't had a UTI for a year.
As Geaton said D-Mannose. I have recommended it but haven't checked out if its worked.