In taking Yaz and having it clot up my blood so badly, that I had stroke symptoms, I had some blood testing done. The doctor ordered a "Thrombophilia" test. The results came back with me being positive for MTHFR. A genetic blood clotting disorder. The type I have is very treatable with Folic Acid, Vitamin B and Baby Aspirin. But no birth control pills for me. Estrogen causes major clotting. And I could end up with a stroke or die. Considering many people have this disorder and don't even know it, I am surprised how birth control pills are handed out like candy, without these things being taken in to consideration.