Does cod liver oil effect birth control pills?

No: Cod liver oil contains high levels of vitamin A and vitamin D. Is there a reason to believe that you are deficient in those?? Do you liv above the Arctic Circle?? Or work at the South Pole station?? Or do you have lupus where you really should have very limited sun exposure? Just eat a good varied diet and you should get more than enough A and D. And NO, it should not affect BCP absorption!