Could anyone tell me what the difference is between the estrogen in birth control pills and Premarin? I take 0.9 mgs. Premarin (had hysterectomy years ago, but kept ovaries) and know that the estrogen in Premarin is not natural and is made from horse urine, but was not sure what the estrogen in the "low dose birth control pills" that a lot of people have been prescribed. A co worker told me that she thought the estrogen in bcp's was made from cow's uring-not sure if that is true. I just wondered if there was a big difference, and if not, why such a big deal is made about the safety of Premarin but not the safety of birth control pills. Any ideas?