It's not a real common occurance but one of the side efects of birth control pills is clots. I have a history of clots from injury and my dr would not give me the B C pills for all the $ in the world. I, too am an RN. Recently had major surgery and was given heparin as preventative maintenance for posssibility of clots. I repeat, it is not real common, but the fact does exist that clots can happen with the use of the pills.