If you're taking birth control pills and prenatal vitamins at the same time, you might be wondering whether there are any special considerations or side effects you need to take into account. There aren't; birth control pills don't interact with prenatals. However, there's really very little reason you should ever use both at once.
Birth Control Pills
Birth control pills consist of hormones that are quite similar in composition to those your body produces naturally during the course of your regular menstrual cycle. The supplemental hormones "fool" your ovaries so you don't release an egg when you would normally ovulate each month. This prevents you from conceiving. During the last week of your pill cycle, you take placebo pills without hormones--these cause you to menstruate.
Prenatal vitamins are nothing more than regular multivitamin and mineral supplements. The only difference between them and regular women's vitamin and mineral supplements is that they have more folic acid and more iron. The folic acid helps with your embryo's neural tube formation--this structure becomes the brain and spinal cord. The iron increases your blood volume, explain Drs. Michael Roizen and Mehmet Oz in their book "You: Having A Baby."
Taking Both at the Same Time
There are side effects associated with both the pill and prenatals. The pill can cause headaches, breast tenderness and possibly even blood clots--though these are rare--according to KidsHealth. Prenatal vitamins, on the other hand, generally have mild side effects, including gastric upset and constipation. If you take both the pill and prenatal vitamins, you might experience the side effects of each, but taking them together won't cause additional side effects.
One thing to think about if you're taking both prenatal vitamins and the pill is whether you really need both. Prenatal vitamins are formulated for women who are trying to conceive or are already pregnant--if you're on birth control, you don't fall into either of these categories. If you're not pregnant or trying to conceive, prenatal vitamins hold no particular benefit for you, and they're much more expensive than regular multivitamins.