Benefits and Risks of Dietary Supplements

Dietary supplements have both benefits and risks.
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Dietary supplements are products designed to augment your daily intake of nutrients, including vitamins and minerals. Many are safe and offer significant health benefits, but there are some that pose health risks, especially if overused. Dietary supplements include amino acids, fatty acids, enzymes, probiotics, herbals, botanicals, and animal extracts.

In addition to vitamins and essential minerals, popular supplements include:


Normally, most people should be able to get all the nutrients they need from a balanced diet. However, supplements can provide you with extra nutrients when your diet is lacking or certain health conditions (such as cancer, diabetes, or chronic diarrhea) trigger a deficiency.

In most cases, a multivitamin/mineral supplement will provide all the micronutrients your body needs. They are generally safe because they contain only small amounts of each nutrient (as measured by the daily value, or DV).

Individual nutrients are available as supplements, usually in doses larger than your typical multivitamin. They can be used to treat a deficiency, such as an iron deficiency, or reduce the risk of a medical condition, such as hypertension.

For example, large doses of vitamin B3 (niacin) may help raise "good" high-density lipoprotein (HDL) cholesterol, while folic acid has long been used to reduce the risk of a birth defect called spina bifida. Antioxidants, such as vitamin C and vitamin E, may reduce the toxic effect of chemotherapy drugs (allowing patients to tolerate larger doses of chemo).

Unless a specific deficiency is identified, a supplement is usually not necessary if you eat and exercise properly. The appropriate use of supplements can help you avoid side effects and toxicities associated with overuse.


In the United States, dietary supplements are not regulated as strictly as pharmaceutical drugs. Manufacturers do not have to prove that they are either safe or effective. The U.S. Food and Drug Administration (FDA) doesn't even determine whether dietary supplements are effective before they are shipped to market shelves.

The FDA does maintain a list of tainted or potentially harmful products marketed as dietary supplements. The worst offenders are usually weight loss aids, "natural" sexual enhancement pills, and supplements targeted at bodybuilders.

Supplement manufacturers have to follow certain labeling guidelines, including what they can say and not about the purported benefits. That doesn't stop manufacturers from claiming, often misleadingly, that their product can "boost the immune system" or "treat arthritis" even if there is little scientific evidence to support the claims. Generally speaking, the FDA only acts on the most serious infractions.

Potential Problems

Large doses of certain nutrients can have adverse effects. You can even overdose on certain supplements, risking serious harm and death. Among some of the harmful interactions or dosing concerns:

  • Vitamin K can reduce the effectiveness of blood thinners like Coumadin (warfarin).
  • Vitamin E can increase the action of blood thinners, leading to easy bruising and nosebleeds.
  • St. John’s wort can accelerate the breakdown of many drugs, including antidepressants and birth control pills, thereby reducing their effectiveness.
  • Vitamin B6 (pyridoxine), when used for a year or more at high doses, can cause severe nerve damage. Vitamin B6 can also reduce the effectiveness of the anti-seizure drug Dilantin (phenytoin) and levodopa (used to treat Parkinson's disease). 
  • Vitamin A used with retinoid acne medications such as Accutane (isotretinoin) and Soriatane (acitretin) can cause vitamin A toxicity.
  • Iron and calcium supplements can reduce the effectiveness of antibiotics, namely tetracyclines and fluoroquinolones, by as much as 40%.
  • Vitamin C can cause diarrhea when taken in doses higher than the gut can absorb (but some patients can tolerate 5,000mg to 25,000mg per day).
  • Selenium, boron, and iron supplements can be toxic if taken in large amounts.

Speak with a healthcare provider about any supplements you plan to take as well as any medications you are currently taking, whether they be pharmaceutical, over-the-counter, herbal, traditional, or homeopathic.

For the utmost safety and quality, choose supplements tested and approved by a certifying body such as the U.S. Pharmacopeia (USP). Never use expired supplements.

9 Sources
Verywell Fit uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. U.S. Food and Drug Administration. Tips for older dietary supplement users.

  2. Afolayan AJ, Wintola OA. Dietary supplements in the management of hypertension and diabetes - a reviewAfr J Tradit Complement Altern Med. 2014;11(3):248-258. doi:10.4314/ajtcam.v11i3.35

  3. National Institutes of Health Office of Dietary Supplements. Niacin fact sheet for health professionals.

  4. Centers for Disease Control and Prevention. Folic acid helps prevent some birth defects.

  5. Singh K, Bhori M, Kasu YA, Bhat G, Marar T. Antioxidants as precision weapons in war against cancer chemotherapy induced toxicity: Exploring the armoury of obscurity. Saudi Pharm J. 2018;26(2):177-190. doi:10.1016/j.jsps.2017.12.013

  6. U.S. Food and Drug Administration. Tainted products marketed as dietary supplements.

  7. U.S. Food and Drug Administration. Center for Biologics Evaluation and Research 2003.

  8. U.S. Food and Drug Administration. Fortify your knowledge about vitamins.

  9. National Institutes of Health Office of Dietary Supplements. Dietary supplements: What you need to know.

Additional Reading

By Shereen Lehman, MS
Shereen Lehman, MS, is a former writer for Verywell Fit and Reuters Health. She's a healthcare journalist who writes about healthy eating and offers evidence-based advice for regular people.