Sorry, I think you should know, wood586 is slightly wrong. I did my undergraduate research paper on rbst and milk.
rBST is a synthetic version of the cow's own growth hormone (BST). It does not change their metabolism and make them eat more. It works by increasing the levels of insulin-like growth factor 1 (called IGF-1, and it's unrelated in function to insulin). This IGF-1 creates an environment within the cow suited to cell growth, which in turn makes them grow larger.
In dairy cows, this means the mammory glands will produce more milk with the same amount of feed they were originally getting. rBST is NOT passed on in the milk in any higher quantity than is normal for milk, and it is denatured during pasteurization anyways. The problem lies in the IGF-1. Humans and cows have the EXACT same IGF-1, which means the human endocrine system cannot distinguish the difference between human IGF-1 and cow IGF-1. This means that the IGF-1 that makes it into your digestive tract (which is entirely possible and very common when in the presence of the milk protein casein) will be picked up by the bloodstream and utilized by your body.
Will this make you grow? No. There is probably not enough IGF-1 to make much of a difference in an average, healthy adult. However, people who are at high-risk for cancer of the breast, colon, or prostate, already have elevated levels of IGF-1 in their systems. Since IGF-1 causes cellular growth, in a cancer victim their body cannot keep this growth at bay and it will continue and continue. Those who are at risk for those cancers and drink regular milk, yes even organic milk, are increasing their risk for cancer because all milk has IGF-1. Thats why it is recommended that they abstain from any dairy products.
So, rBST is fairly harmless to the average human, but in a high-risk person that subtle increase in IGF-1 caused by the rBST could be the bit that tips them over the edge into cancer.
Organic milk is not made with rBST or any other synthetic antibiotic or hormone. This seasons more favorably for the cow than the actual consumer.
It is unlikely that rBST would do much to a person, but cows treated with rBST have a 20% increase in milk yeild accompanied by a 20% higher rate of utter infections, lesions, and illness. This means they are fed antibiotics in increasing doses. These antibiotics, as well as the bacterias themselves CAN be passed into milk, and the heavy doses also breed conditions for antibiotic-resistant bacteria. Standard milk is pasteurized at 140 degrees, but strep bacteria is killed at 190. Sure, there are dairy plants that pasteurize at 200, but they are few and far between, plus that information is not readily available to the public.
All milk contains the strep. bacteria, even organic milk. Its just somethinig that is naturally in milk. When the milk is pasteurized at 190 or above for at least 3 minutes, the risk of you contracting the strep. bacteria is almost nil. But we wonder why almost every child gets strep throat and the dairy industry pushes 3 servings a day on parents.
So, if you are a big milk drinker, organic is certainly better. Not perfect, but better.
I never drank milk and I have never had strep. Even when my classmates had strep I never got it. Possibly a coincidence, but who knows.