Some of the best-known medicines from the local drugstore can be harmful to pregnant women, yet many mothers-to-be regularly take them. Studies show that, on average, women take between one and four medications during pregnancy, not including vitamins or minerals. An estimated 60 percent of pregnant women use over-the-counter drugs, not always with physician oversight.

To help you and your doctor make more-informed choices about which medications to take, we've identified 10 commonly used ingredients found in OTC drugs that are risky for pregnant women, and offer safer alternatives. For example, moms-to-be should not take castor oil and should avoid aspirin during all stages of pregnancy. During the first and second trimesters of pregnancy, they should use the following products with caution and avoid them entirely during their third trimester: bismuth subsalicylate (Pepto Bismol), chlorpheniramine (Actified, Chlor-Trimeton, and many other combination cold medicines), ibuprofen (Advil, Motrin), and naproxen (Aleve).

When choosing an OTC medicine, you'll need to be a careful label reader since brand names can be deceiving. For example, while acetaminophen (Tylenol) is considered relatively safe for use in pregnancy, some combination products that include the brand name "Tylenol," such as Tylenol Allergy Sinus Maximum Strength, contain chlorpheniramine.

Most medicines approved by the Food and Drug Administration are not tested on pregnant women because of ethical concerns. In fact, there is no pregnancy safety data for more than 80 percent of prescription and OTC drugs, making it extremely difficult for doctors and pharmacists to provide guidance. Currently, the FDA uses a rating system for more than 270 active ingredients in prescription and OTC drugs on a scale of A, B, C, D, and X. But in the coming months the FDA will no longer use that rating scale and instead will provide study data on how drugs affect pregnancy, lactation, and fetus development.

Pregnant women and women considering pregnancy should approach the use of all drugs (OTC and prescription) and dietary supplements with caution and use them only after discussion with their physician.