Re: Why does birth control cause heart disease/strokes/blood clots?
The theory is that when a woman is pregnant, the hormones in her blood signal the blood to become "stickier" so that it can clot more easily. This is to prepare the body for birth, to make sure the mother does not bleed to death.
The hormones in the pill/patch/ring mimic pregnancy hormones, so the side effect is the "stickier" blood.
Estrogen is thought to be the main hormone responsible for the slight increase in clotting, so that is why progestin-only methods are generally able to be taken by people who previously had a clot on a combined method.
Also, the pill does not cause heart disease. It can possibly cause a clot that could result in a pulmonary embolism, stroke, or heart attack, but it does not cause heart disease.