Do bcp's still work to prevent pregnancy even if you're allergic to it?

? allergic ?: BC pills are composed of hormones similar to those made by the human body. You don't get "allergic" to them. There are side effects that effect some people and these side effects can be bad enough that people change or stop them. If someone cannot tolerate the pill, they need to use condoms or a non-hormonal IUD.The pill can't work if you don't take it as prescribed.