it contains three types of lactic acid bacteria. it is basically a probiotic. it is usually used most for people with a problem with an overgrowth of yeast in their gi tract. it is supposed to help get rid of the yeast problem without having to stick to the very strict anti-candida diet.
because these bacteria produce lactic acid (as a by product) this makes the environment in your gi tract less hospitable to the yeast. it helps kill them off that way.
i've used it for candida. i don't use it anymore because i've tried another probiotic i think is even better.