What Are the Side Effects of Prenatal Vitamins?

A pregnant woman swallows a vitamin with a glass of water in the kitchen.
Image Credit: Александр Ермолаев/iStock/Getty Images

A growing baby requires a lot of nutrients that most moms-to-be don't get through their diets alone. Prenatal vitamins ensure that you and your baby are getting the vitamins, minerals and nutrients you need so you can stay healthy and your baby can develop properly. Most women can take prenatals with very few side effects or problems, but some do experience unpleasant reactions that make taking the vitamins difficult.


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Bowel Problems

Getting enough iron is extremely important when you're pregnant because it helps your body make more hemoglobin to carry oxygen in your blood, nourishes your baby and placenta, and helps prevent iron-deficiency anemia, which can lead to low birth weight or preterm delivery. Pregnant women need 27 milligrams of iron daily, and many prenatal vitamins contain 30 milligrams. The most common side effect of iron is constipation, but it can also cause diarrhea in some cases. It's normal if your stools look a bit darker when you start taking a prenatal vitamin. If you're having bowel problems, talk to your doctor or midwife about the possibility of taking a prenatal with less iron or taking a separate iron supplement and splitting up your daily iron needs into several doses.


Nausea and Vomiting

Many pregnant women experience nausea and vomiting regularly. In some cases, prenatal vitamins can cause these symptoms. While you might be able to deal with slight queasiness, if you find yourself throwing up regularly after taking your prenatal vitamin, your body probably isn't absorbing what it needs from the supplement. Taking your vitamin at night right before you go to bed can help minimize these symptoms. You may find that taking it right after a meal helps as well. Discuss your concerns with your doctor or midwife if you're having trouble swallowing your vitamins or can't keep them down. She may prescribe a smaller pill with a smooth coating that's easier to swallow, or she may suggest a chewable vitamin.


Other Side Effects

Some women experience headaches when taking prenatal vitamins. It's common to have headaches during pregnancy, but seek medical attention if your headache is severe or if you suspect an overdose. Some of the vitamins in prenatals, particularly B vitamins, can cause your urine to change color to a bright yellow or greenish color. This side effect is harmless, but discuss it with your doctor or midwife if you have any questions. You may notice a metallic taste in your mouth when taking your vitamins. This is normal and can be due to the increasing estrogen levels that occur during pregnancy, but your vitamin may play a role in this side effect as well, explains the Pregnancy Corner website. If you find the taste bothersome, try consuming something acidic, like an orange or lemonade, at the same time. Gargling with saltwater or drinking beverages flavored with ginger can also help.


Overdose Concerns

While the vitamins in prenatals are vital, taking too much of them can cause serious side effects and problems for you and your baby. Overdose symptoms include stomach pain, a tingling feeling around your mouth, severe headache or backache, blood in your urine, and muscle or joint pain, according to the Dartmouth-Hitchcock Norris Cotton Cancer Center. Taking two prenatal vitamins in a day isn't likely to cause any harm if it's a one-time occurrence, but if you take more than two or experience any overdose symptoms, seek emergency medical attention.