Probiotics are products containing the helpful bacteria (usually Lactobacillus or Bifidobacterium) that normally inhabit the human digestive tract. Most of these "friendly" bacteria occur naturally in cultured milk products, such as yogurt with active cultures or acidophilus milk. You should consider taking probiotic foods or supplements whenever you're on antibiotics, which can wipe out intestinal bacteria indiscriminately, including those that help keep the digestive system functioning normally and may support immune system function. Start taking probiotics twice a day with meals as soon as you start taking antibiotics and continue for a few days after you finish. Look for brands containing Bacillus coagulans (BC-30) or Lactobacillus GG in liquid or capsule form. The dose is one tablespoon of the liquid culture or one to two capsules with meals unless the label directs otherwise. Probiotics are also an effective treatment for diarrhea in children, travelers' diarrhea, lactose intolerance, irritable bowel syndrome and vaginal yeast infections.