Don’t Spend a Lot of Money.Your multivitamin shouldn’t cost more than a few dollars a month. Store brands are often just as effective as name brands. Any brand with the “USP” mark on the bottle is a good one. (“USP” stands for United States Pharmacopeia and means that the supplement has been tested for quality and to ensure it dissolves in your stomach.)

Look Out for Overdoses. Some supplements have 5,000 percent of the daily value for various nutrients—and that’s far more than you need. Megadoses of many vitamins and minerals can actually be dangerous.

Remember It’s a Supplement, Not a Substitute. Supplements can be a helpful addition to a healthy diet, but they can’t replace all the nutrients that come from foods. Taking a supplement is no excuse to eat badly.

Consider Over-50 Supplements. Over-50 supplements can be a good choice for older adults because they are lower in iron—which older people need less of—and higher in vitamin B12—which older people need more of.

Get Personal. Discussing supplements with your physician can help you choose the one that best meets your individual needs. For example, patients taking blood thinners may need supplements without vitamin K, which can interfere with the medication.

Explore the Extras. You may need something in addition to a multivitamin, such as calcium or vitamin E supplements, since many multivitamins don’t contain as much as you may require. But you won’t need supplements with additional vitamin B complexes, since your multivitamin will cover those. Check with your doctor or registered dietitian for details.