Cranberry is known to be taken as for medicinal purpose by the northern Native Americans. The looks and size mimics that of cherries, however the flavor may be very bitter when taken raw. Cranberries are full of powerful phytochemicals that protects your body from pathogens for illness. Among the various polyphenols found in cranberries, the type A proanthocyanidins (PACs) have been studied to have the major effect in preventions of urinary tract infection.
The cause of cystitis is mainly Escherichia coli (E-coli). Type A proanthocyanidins (PACs) of cranberries prevent E-coli from sticking to urinary tract such as bladder as shown in the picture. The E-coli bacteria that did not stick to the mucous membranes of the bladder wall or the urinary tract will wash away with urine, therefore it is free from UTI (cystitis).
According to some research, the cranberry outperforms over an antibiotics (trimethoprim) which is used mainly in the treatment of bladder infections, in preventing the recurrence of UTI. The purpose of the research was to compare the effectiveness of cranberry extract with low-dose of trimethoprim in prevention of UTI. Based on the clinical and statistical comparison, it was concluded that trimethoprim had a very limited advantage over cranberry extract in older women, and it also had more adverse effect. They recommend to weigh up for a cheap, natural product like cranberry extract whose use does not carry the risk of antimicrobial resistance or super-infection with Clostridium difficile.
There are quite a lot of people who have cystitis have been taking cranberry juice, but most of the commercial cranberry juice is made with lots of sweeteners and sugar. Some clinical studies performed to show most of commercial cranberry juice to have no, or minimal effect on cystitis for not having enough cranberry components, but rather it is just a sweetened beverage.
Dried cranberries distributed on the market are mostly dried by sugar or artificial sweeteners as well due to its raw flavor being highly sour and bitter. Therefore, you may want to look away since you will be consuming sugars unnecessarily. Diabetics need to be cautious for these as well as in commercial juice.
Cran-Max®, (http://www.webmd.com/drugs/2/drug-92539/cran-max-oral/details) the cranberry extract in powder, in capsule, is recommended because no chemical additives such as preservatives, sugars, water, colorants and flavoring. Steady intake…Cranberry is recommended for steady intake of at least a couple of months to be more effective to prevent the bladder infection, rather than taking a few once you notice a symptom of a cystitis.
Reference:  Marion E.T. McMurdo, I. Argo, G. Phillips, F. Daly, Peter Davey (Nov. 2008). Cranberry or trimethoprim for the prevention of recurrent urinary tract infections? A randomized controlled trial in older women. Journal of Antimicrobial Chemotherapy. 2009 Feb; 63(2): 389–395.