CFUs are Colony-forming Units. This indicates how many viable cells, or active microorganisms, are included in a probiotic product. CFUs are measured per gram or per milliliter. The recommended dose is 5 to 15 billion CFUs per serving of a probiotic drink or supplement. Depending on your health goals, you might choose to take probiotics a few days a week to maintain gut health, or daily for a two-week period to combat a particular complaint, like a yeast infection. A dose smaller than 5 billion CFUs is ineffective for most purposes. If your probiotic drink doesn't have enough CFUs in it, you may enjoy the flavor, but you probably won't get notable health benefits.