I haven't really had severe side effects yet. I have only been on yaz for 3 months. But so far i have the fallowing side effects: Head aches i have been taking advil like its candy. Mood swings, pain while intercourse, abdominal pain, and decreased/zero sex drive. I am already a hypocondriac (sp) so i figured i am making it up. But who would make up not wanting to have sex. lol i will give it a few more months to level my hormones and maybe i will be ok.