Introduction to Dietary Supplement Use

What's in a bottle?

A selection of vitamins and herbal supplements
Rafe Swan/Getty Images

Dietary supplements are a topic of great public interest. Whether you are in a store, using the Internet, or talking to people you know, you may hear claims about their health benefits. How do you find out whether "what's in the bottle" is safe to take and whether science has proven that the product does what it claims? 

What Are Dietary Supplements?

Dietary supplements (also called nutritional supplements, or supplements for short) are defined by the following criteria:

  • Are taken by mouth.
  • Contain a "dietary ingredient" intended to supplement the diet. Examples of dietary ingredients include vitamins, minerals, herbs (as single herbs or mixtures), other botanicals, amino acids, and dietary substances such as enzymes and glandulars.
  • Come in different forms, such as tablets, capsules, softgels, gelcaps, liquids, and powders.
  • Are not represented for use as a conventional food or as a sole item of a meal or the diet.
  • Are labeled as being a dietary supplement.

Dietary supplements are sold in grocery, health food, drug, and discount stores, as well as through mail-order catalogs, TV programs, the Internet, and direct sales.

Why Do People Take Supplements?

People take supplements for many reasons. A scientific study on this topic was published in 2002. Over 2,500 Americans reported on supplements they used (given the categories of vitamins/minerals and herbal products/natural supplements) and the reasons for taking them. Their responses are summarized below:


  • Health/good for you - 35%
  • Dietary supplement - 11%
  • Vitamin/mineral supplement - 8%
  • Prevent osteoporosis - 6%
  • Physician recommended - 6%
  • Prevent colds/influenza - 3%
  • Don't know/no reason specified - 3%
  • Immune booster - 2%
  • Recommended by friend/family/media - 2%
  • Energy - 2%
  • All others - 22%


  • Health/good for you - 16%
  • Arthritis - 7%
  • Memory improvement - 6%
  • Energy - 5%
  • Immune booster - 5%
  • Joint - 4%
  • Supplement diet - 4%
  • Sleep aid - 3%
  • Prostate - 3%
  • Don't know/no reason specified - 2%
  • All others - 45%

How Can I Get Science-Based Information on a Supplement?

There are several ways to get information on supplements that is based on the results of rigorous scientific testing, rather than on testimonials and other unscientific information.

Ask your health care provider. Even if your provider does not happen to know about a particular supplement, he or she may have professional resources to turn to about uses, potential risks, and drug interactions. 

Using Supplements Safely

If you are interested in using a supplement as complementary and alternative medicine (CAM), keep in mind:

1. It is important to talk to your healthcare provider (or providers, if you have more than one) about the supplement before using it. This is for your safety. It is especially important to talk to your provider if you:

  • Are thinking about replacing your regular medical care with one or more supplements.
  • Are taking any medications (whether prescription or over-the-counter). Some supplements have been found to interact with medications (see below).
  • Have a medical condition.
  • Are planning to have surgery. Certain supplements may increase the risk of bleeding or affect anesthetics and painkillers.
  • Are pregnant or nursing a baby.
  • Are thinking about giving a child a supplement. Many products being marketed for children have not been tested for their safety and effectiveness in children.

2. Do not take a higher dose of a supplement than what is listed on the label, unless your health care provider advises you to do so.

3. If you experience any side effects that concern you, stop taking the supplement, and contact your provider. You can also report your experience to the U.S. Food and Drug Administration's (FDA) MedWatch program, which tracks consumer safety reports on supplements.

5. For current information from the Federal Government on the safety of particular supplements, check the "Alerts and Advisories" section of the National Center for Complementary and Integrative Health Web site (NCCIH) or the FDA Web site.

Supplements and Drugs Can Interact

When this happens, it can change the way the drugs you take respond or react in your body.

  • St. John's wort can increase the effects of prescription drugs used to treat depression. It can also interfere with drugs used to treat HIV infection, to treat cancer, for birth control, or to prevent the body from rejecting transplanted organs.
  • Ginseng can increase the stimulant effects of caffeine (as in coffee, tea, and cola). It can also lower blood sugar levels, creating the possibility of problems when used with diabetes drugs.
  • Ginkgo, taken with anticoagulant or antiplatelet drugs, can increase the risk of bleeding. It is also possible that ginkgo might interact with certain psychiatric drugs and with certain drugs that affect blood sugar levels.

Does "Natural" Always Mean "Safe"?

There are many supplements, as well as many prescription drugs, that come from natural sources and are both useful and safe. However, "natural" does not always mean "safe" or "without harmful effects." Consider mushrooms that grow in the wild—some are safe to eat, while others are poisonous.

The FDA issues warnings about supplements that pose risks to consumers, including those used for CAM therapies. Examples include kava, comfrey, and ephedra. The FDA found these products of concern because they:

  • Could damage health—in some cases severely.
  • Were contaminated—with other unlabeled herbs, pesticides, heavy metals, or prescription drugs.
  • Interacted dangerously with prescription drugs

Does the Federal Government Regulate Supplements?

Currently, the FDA regulates supplements as foods rather than drugs. In general, the laws about putting foods (including supplements) on the market and keeping them on the market are less strict than the laws for drugs. Here are some ways that they differ.

  • Human research studies proving the safety of a supplement are not required before the supplement is marketed (unlike prescription or over-the-counter drugs).
  • The manufacturer does not have to prove that the supplement is effective. The manufacturer can say that the product addresses a nutrient deficiency, supports health, or reduces the risk of developing a health problem. If the manufacturer does make a claim, it must be followed by the statement "This statement has not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease."
  • The manufacturer does not have to prove supplement quality. Specifically:
    • The FDA does not analyze the content of dietary supplements.
    • In addition, at this time, supplement manufacturers must meet the requirements of the FDA's Good Manufacturing Practices (GMPs) for foods. GMPs describe conditions under which products must be prepared, packed, and stored. Food GMPs do not always cover all issues of supplement quality. Some manufacturers voluntarily follow the FDA's GMPs for drugs, which are stricter.
    • Some manufacturers use the term "standardized" to describe efforts to make their products consistent. However, U.S. law does not define standardization. Therefore, the use of this term (or similar terms such as "verified" or "certified") does not guarantee product quality or consistency.
    • If the FDA finds a supplement to be unsafe once it is on the market, only then can it take action against the manufacturer and/or distributor, such as by issuing a warning or requiring the product to be removed from the marketplace.

The federal government regulates supplement advertising through the Federal Trade Commission. It requires that all information about supplements be truthful and not mislead consumers.

What's in the Bottle Does Not Always Match What's on the Label

A supplement might not contain the ingredient that is listed on the label (such as plant species). For example, one study that analyzed 59 preparations of echinacea found that about half did not contain the species listed on the label.

Supplements may also contain higher or lower amounts of the active ingredient. For example, a study of ginseng products found that most contained less than half the amount of ginseng listed on their labels.

Supplements may also be contaminated, which of course will not be disclosed on the label.

Is the US Government Supporting Research On Supplements?

Yes, the National Center for Complementary and Integrative Health (NCCIH, part of the National Institutes of Health) is funding most of the nation's current research aimed at increasing scientific knowledge about supplements—including whether they work; if so, how they work; and how purer and more standardized products could be developed. Among the substances that researchers are studying are:

  • Yeast-fermented rice, to see if it can lower cholesterol levels in the blood
  • Soy, to see if it slows the growth of tumors
  • Ginger and turmeric, to see if they can reduce inflammation associated with arthritis and asthma
  • Chromium, to better understand its biological effects and impact upon insulin in the body, possibly offering new pathways to treating type 2 diabetes
  • Green tea, to find out if it can prevent heart disease
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