Also buy only specific strains, ie those that are able to implant and colonise your gut, many strains cannot. They just put them in yogurt becos it makes the yogurt taste good. Also I notice that most pple with cfs have got gut dysbiosis in the large intestines and not the small intestines. You would need anerobic probiotics in the Bifidobacteria family for this purposes and the L. strains will have limited effect.