In your gut you have bacteria. If you take antibiotics...this will kill the good and the bad bacteria in your gut. Prob. is we need the good bacteria for our immunity (if I have this wrong...please someone chime in and correct me!) Probiotics replace all the bacteria in the gut. You can get probiotcs....acidophilos, bifidus, and others...from cultured yogurt/soy yogurt or from a powder or a pill at a health food store.