Birth control pills: what are the worst side effects?

Depends on the pt: Some commonly reported side effects of birth control pills are unscheduled bleeding, lighter/shorter periods, missed periods, nausea, upset stomach and headaches. Each individual patient may experience one or more of these or none at all. If you do experience something you can't tolerate, you can always try another formulation. You have many pills combos to choose from. Talk to your doctor.