The amount taken varies depending on what you are trying to treat or if you're just going for a maintenance amount. Usually the directions listed on the bottle will work for just about any of the symptoms of deficiency. As a general rule, there should be no less than 1 billion active organisms per gram and they should be taken with food and stored in a cool place. Heat and freezing will kill acidophilus. It is best to get an acidophilus supplement
that is has an enteric coating as this helps the organisms to be delivered to the intestine unharmed.
The only side effects may be a little gas for maybe the first week as your body adjusts to the bacterial shift. After the first week the gas will subside.