"There is no question that some hormone, both in treated and untreated cows, does pass into the milk. This is of no apparent consequence because bovine growth hormone is inactive in humans. In any case, like any other protein, it is broken down in our digestive tract. BGH actually exerts its milk producing effects by triggering the synthesis of a protein known as insulinlike growth factor-I, or IGF-I in the cow's liver. This protein is always present in milk but is found in higher concentrations in the milk from BGH treated animals. These elevated levels are still within the range of variation for untreated milk, and in fact no technology exists that can determine whether a specific milk sample came from a treated or an untreated cow. IGF-I is also a protein hormone, and therefore does not survive the digestion process.

Arguments about possible health consequences of BGH or IGF-I as present in milk are based more on emotion than on science."

McGill University - Office for Science & Society