Do prenatal vitamins interact negatively with medications?

Possibly. There are many medications and many components to prenatal vitamins. Many medications increase the need for certain vitamins and minerals and some are not absorbed well with certain minerals like iron, calcium, and magnesium . You would have to look at the particular medication to determine if there is a negative or positive interaction.
Yes. Some yes. You need to ask your pharmacist about possible interactions between your medications and your prenatal vitamins.

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Is there really a best time on taking medications? Like Claritin (loratadine) and prenatal vitamins?

Antihistamines late. It has become more apparent over the past few years that taking an antihistamine in the evening can be better, as it will be in full force working the next day when you wake up. Read more...