Drug interactions: Some supplements, like antioxidants or vitamin E, can interact with existing medications you may be taking. For example, vitamin E can amplify the effects of blood thinners. If you're taking prescription medication, check with your doctor or pharmacist before adding a multivitamin to your diet.

Health history and vitamin deficiencies: Vitamins are intended to fill in the gaps left by our diet. If you don't have any gaps, you may not need to take a vitamin supplement. What's best for you, though, will depend on your health history and blood work -- including any vitamin deficiencies you may have. That's why it's best to talk with your doctor about their recommendations for a multivitamin or supplement, so you can get the most tailored advice.

Budget: There is a quality multivitamin at every budget level. However, the ones with the most personalization or special additives -- like probiotics -- will cost more. Deciding how much you're willing to spend will help you narrow down your search. 

Dosage: If only all vitamins were one pill. That's not the reality of the vitamin market. Many of the best supplements require that you take five or more capsules a day. That's not ideal for some people.

Vitamin form: For folks who have difficulty swallowing pills, you should consider the form your multivitamin comes in. Some tablets or capsules are larger than others and may impede your ability to consistently take them. Consider one of the best gummy vitamins for women over 50 instead.