Listen to the Cancer.Net Podcast: Dietary and Herbal Supplements, adapted from this content.

Key messages:

• It's important to be an informed consumer before taking dietary and herbal supplements.
  
  
• Talk with your doctor to learn about possible benefits and risks, interactions with current cancer treatments, side effects, and other considerations.

People living with cancer may consider taking dietary and herbal supplements as a way to boost health, improve nutrition, or reduce treatment side effects. It is important to discuss the possible benefits and risks of specific supplements with your doctor before taking them.

Types of supplements

• Dietary supplements. These products have one or more dietary ingredients—including vitamins, minerals, herbs, enzymes, amino acids, and hormones—that people may decide to add to their regular diet. Dietary supplements can be bought without a prescription in pharmacies, grocery stores, and health food stores as a pill, capsule, tablet, liquid, or powder.
  
  
• Herbal supplements or botanicals. These products—including tablets, capsules, powders, and tea bags—are dietary supplements that contain plants or ingredients from plants.

Supplements as complementary and alternative medicine

Supplements are considered part of complementary and alternative medicine (CAM), a diverse group of treatments, techniques, and products that are not considered conventional medicine. A conventional treatment has been scientifically tested, found to be safe and effective, and approved by the U.S. Food and Drug Administration (FDA). Supplements can be used as either complementary medicine or alternative medicine. Learn more about the definitions of complementary medicine and alternative medicine.

For example, if someone takes an herbal supplement to help reduce nausea during chemotherapy, it is considered a complementary therapy. Many supplements can be safely used with a doctor's guidance to manage side effects of conventional treatment or to improve a patient's physical or emotional well-being.

Meanwhile, if someone takes large doses of that same herbal supplement in an effort to cure the cancer, rather than undergoing chemotherapy, it is considered an alternative therapy. Claims that supplements can cure cancer have not been proven, and some supplements can be harmful to a person's health.

Evaluating the safety of supplements

It can be difficult to determine the safety and effectiveness of dietary supplements. Information about dietary supplements is often based on anecdotal evidence (people's personal observations) instead of scientific studies. People commonly believe that, because herbs and other supplements are "natural" and have been used for centuries for medicinal purposes, they are safe. However, safety varies depending on the dietary supplement’s ingredients, dose, preparation, and effect on the body.

The FDA regulates dietary supplements differently than prescription or over-the-counter medications; it does not approve dietary supplements as safe and effective before they are sold. The FDA can only claim that a supplement is unsafe after consumers have reported problems with it. Thus, the degree of quality control depends on the manufacturer, the supplier, and others in the supplement's production process.

It is important to note that claims made on supplement labels can be confusing. The FDA allows dietary supplements labels to include one of three types of claims: a health claim (which describes an FDA-approved link between a food, food component, or dietary supplement and a disease or health-related condition), a nutrient content claim (which describes the level of a nutrient or dietary substance contained in the product), and a structural or functional claim (which describes how a dietary ingredient is intended to affect the body’s structure or function). Product labels with a structural or functional claim must also include a disclaimer that reads, "This statement has not been evaluated by the FDA. This product is not intended to diagnose, treat, cure, or prevent any disease." In other words, the claim probably has not been rigorously tested and may not be true.

People undergoing cancer treatment must be extremely cautious about the safety of dietary supplements because some can interfere with surgery, chemotherapy, and radiation therapy. For instance, the herb kava can interfere with anesthesia for surgery, and some doctors believe that taking antioxidants may decrease the effectiveness of treatment.

Talking with your doctor about supplements

Deciding whether, when, and how to use a dietary supplement to complement standard cancer treatments can be complicated. It's important to be an informed consumer and discuss the choice with a doctor, addressing the following considerations:

• Possible benefits and risks, depending—in part—on personal medical history
  
  
• Possible interactions with current cancer treatments
  
  
• Possible side effects
  
  
• Dosage levels and length of treatment
  
  
• New information about the supplement, preferably from clinical trials, rather than personal stories

Learn more about questions to ask when considering CAM.

Warnings about supplements

• Some supplements can cause serious side effects—such as high blood pressure, nausea, diarrhea, constipation, fainting, headaches, seizures, heart attack, or stroke—even when taken at the recommended dose. Contact your doctor immediately if you experience any harmful side effects.
  
  
• Some supplements’ ingredients may interfere with prescription and over-the-counter medications you may already be taking. In addition, as stated above, some can interact with cancer treatments.
  
  
• Certain dietary supplements may be unsafe if you have specific health problems, including high blood pressure, diabetes, mental health conditions, or heart disease.

Recommendations if you decide to use supplements

• Purchase only single-ingredient products approved by your doctor that clearly show how much each dose contains, and use brands from companies you or your doctor know are reputable. Some supplements have been found to be contaminated with other unlabeled herbs, pesticides, prescription drugs, heavy metals, or other substances.
  
  
• Look for a certification mark or seal from an independent, third-party organization, such as U.S. Pharmacopoeia, the Good Housekeeping Research Institute, or ConsumerLab.com. Although tests differ, such labels indicate that the supplement has met certain manufacturing standards.
  
  
• Check the product label to see whether the supplement has been scientifically tested. Contact the manufacturer for the test results, and ask your doctor to explain anything that isn't clear.
  
  
• Be skeptical of supplements' label claims, particularly those that claim to cure cancer since no single device, remedy, or treatment can treat all cancers.

More Information

Complementary and Alternative Medicine

Vitamins and Minerals

Additional Resources

National Center for Complementary and Alternative Medicine: Using Dietary Supplements Wisely

National Institutes of Health’s Office of Dietary Supplements: Background Information

Memorial Sloan-Kettering Cancer Center: About Herbs, Botanicals & Other Products