I looked into all this a long time ago, and I'd be failing in my duty as site sceptic, if I didn't point out
this
Summary. Authors' conclusions
After a thorough search, no RCTs which assessed the effectiveness of cranberry juice for the treatment of UTIs were found. Therefore, at the present time, there is no good quality evidence to suggest that it is effective for the treatment of UTIs. Well‐designed parallel group, double blind studies comparing cranberry juice and other cranberry products versus placebo to assess the effectiveness of cranberry juice in treating UTIs are needed. Outcomes should include reduction in symptoms, sterilisation of the urine, side effects and adherence to therapy. Dosage (amount and concentration) and duration of therapy should also be assessed. Consumers and clinicians will welcome the evidence from these studies.
Plain language summary
Still waiting for evidence about whether cranberries are a useful treatment for urinary tract infections
This has all been known for decades, but people seem to want to trust social media, and their hairdresser's sister in law, for medical information rather than accredited, peer reviewed, published research. If you had to market a fairly unpleasant tasting berry - best to endow it with some medicinal properties, and usually give a reference to Red Indians swearing by it

I note that patients always seem to take antibiotics at the same time as cranberry juice, and I'm sure no doctor would just prescribe the fruit juice on its own.
However - once again - take whatever conclusion from this as you wish.
