You should not take Arimidex if you are breastfeeding, pregnant, trying to get pregnant, or if there is any chance that you could be pregnant. Arimidex may cause damage to developing embryos. You should use an effective non-hormonal type of birth control -- such as condoms, a diaphragm along with spermicide, or a non-hormonal . – while you are taking Arimidex. Ask your doctor which type of non-hormonal birth control would be best for you, as well as how long you should use this type of birth control after you stop taking Arimidex.