Supplemental probiotics provide the helpful bacteria (usually Lactobacillus or Bifidobacterium), which normally inhabit the human digestive tract. Most of these "friendly" bacteria occur naturally in cultured milk products, such as acidophilus milk and yogurt with active cultures.
Taken regularly, probiotics can help keep the digestive system in balance and functioning optimally, restore normal flora, and support immune system function, especially when you're taking antibiotics, which can wipe out intestinal bacteria indiscriminately. I also frequently suggest probiotics as an effective treatment for diarrhea, lactose intolerance, irritable bowel syndrome, vaginal yeast infections, oral thrush, Crohn's disease, and ulcerative colitis. When there's a family history of allergy or eczema, babies receiving probiotics in their first six months of life (and whose mothers took probiotics during the last trimester of pregnancy) are less prone to develop skin problems. Children with autism can also benefit from probiotics, possibly because the beneficial bacteria decrease leakage of large molecules from the gut, a process that can trigger immune reactions that affect brain function.
I recommend taking probiotic supplements whenever you're on antibiotics. Take them twice a day with meals as soon as you start your course of medication 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 unless the label directs otherwise. Always check the expiration date to make sure that the bacteria these products contain are alive and in good condition, and look for brands with "colony forming units" (CFUs) in the billions. Be sure to protect your supplements from heat, moisture, and air.
Yes, you can stay on probiotics indefinitely. The only reason to avoid them is if you have had an allergic reaction to lactobacillus, acidophilus, bifidobacterium, or Streptococcus thermophilus.
Andrew Weil, M.D.