Topic Overview

What are dietary supplements?

In the United States, dietary supplements are substances you eat or drink. They can be vitamins, minerals, herbs or other plants, amino acids (the individual building blocks of protein), or parts of these substances. They can be in pill, capsule, tablet, or liquid form. They supplement (add to) the diet and should not be considered a substitute for food.

Dietary supplements are widely available in the United States in health food stores, grocery stores, pharmacies, on the Internet, and by mail. People commonly take them for health-related reasons. Common dietary supplements include vitamins and minerals (such as vitamin C or a multivitamin), botanicals (herbs and plant products, such as St. John’s wort), and substances that come from a natural source (such as omega-3 fatty acids).

Makers of dietary supplements cannot legally say that dietary supplements can diagnose, cure, treat, or prevent disease. But they can say that they contribute to health maintenance and well-being.

People have used the active ingredients in dietary supplements for thousands of years to help health and to treat illness. Sometimes those supplements are the basis for some of today’s common medicines. For example, people have used willow bark tea for centuries to relieve fever. Pharmaceutical companies eventually identified the chemical in willow bark that relieved fever and used that knowledge to produce aspirin.

The U.S. Food and Drug Administration (FDA) does not regulate dietary supplements in the same way that it regulates medicine. A dietary supplement can be sold without research on how well it works.

What are dietary supplements used for?

People use dietary supplements for many health conditions.

• Historically, people have used herbal medicines to prevent illness, cure infection, relieve fever, and heal wounds. Herbal medicines can also treat constipation, ease pain, or act as relaxants or stimulants. Research on some herbs and plant products has shown that they may have some of the same effects that conventional medicines do, while others may have no effect or may be harmful.
• Researchers have studied some natural products and have found them to be useful. Omega-3 fatty acids, for example, may help lower triglyceride levels.

Researchers have found that some supplements do not help prevent or treat certain health problems. For example, beta-carotene and vitamin E do not lower risk of heart disease or heart attack.

Are dietary supplements safe?

Not all herbs and supplements are safe. If you are unsure about the safety of a supplement or herb, talk to your doctor, pharmacist, or dietitian.

Always tell your doctor if you are using a dietary supplement or if you are thinking about combining a dietary supplement with your conventional medical treatment. It may not be safe to forgo your conventional medical treatment and rely only on a dietary supplement. This is especially important for women who are pregnant or breastfeeding.

When using dietary supplements, keep in mind the following.

• Like conventional medicines, dietary supplements may cause side effects, trigger allergic reactions, or interact with prescription and nonprescription medicines or other supplements you might be taking. A side effect or interaction with another medicine or supplement may make other health conditions worse.
• The way dietary supplements are manufactured may not be standardized. Because of this, how well they work or any side effects they cause may differ among brands or even within different lots of the same brand. The form of supplement that you buy in health food or grocery stores may not be the same as the form used in research.
• Other than for vitamins and minerals, the long-term effects of most dietary supplements are not known.