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Dietary Supplements: How To Know What Is Safe
What You Need to Know First

If you are thinking about using dietary supplements such as vitamins, herbs, or any product made from plants (botanicals) as part of your cancer treatment, you need to consider your choice carefully. Right now, few governmental standards are in place to control the production and ensure the safety, effectiveness, and quality of dietary supplements. Although the U.S. Food and Drug Administration (FDA) put out new regulations in 2007 to help improve the safety and consistency of supplements, some of these rules will not be fully in effect until 2010. Even then, there are concerns about what will not change under the new rules. So it still falls to you, the consumer, to gather truthful information about using these products safely.

Like drugs, dietary supplements have risks and side effects. They can usually be used safely within certain dosage guidelines. But, unlike drugs, dietary supplements are mostly "self-prescribed," with little or no input from informed medical sources like doctors, nurses, or pharmacists. There is a lot of wrong information out there. Often, there is not enough reliable information about the safe use and potential risks of dietary supplements.

As part of its activity to monitor supplement safety, the U.S. FDA gathers reports of illness, injury, or reactions from supplements. However, before December 2007, supplement makers were not required to report serious harmful effects to the FDA, so most of these events were not reported. Exposures to supplements (such as vitamins and herbs or botanicals) accounted for nearly 24,000 calls to U.S. poison control centers in 2005 alone. Of these calls, there were more than 212 moderate to severe outcomes, and 13 resulted in deaths. More than 350 of these cases were described as "adverse reactions." It is safe to assume that most people who suffered unexpected side effects, illnesses, or drug interactions from dietary supplements did not call a poison control center. That means that these numbers are likely to be a very low estimate of actual events.

This is not to say that used properly, certain dietary supplements cannot reduce the risk of some diseases, relieve or reduce discomfort caused by certain drugs or conditions, or simply improve your quality of life. However, particularly in the case of people who are getting treatment for cancer, taking dietary supplements can be risky.

For example, some dietary supplements can cause skin sensitivity and severe reactions when taken while receiving radiation treatments. Patients having radiation treatment should talk to their doctors before taking any supplement. Also, patients getting chemotherapy may be at higher risk for drug interaction if they take dietary supplements. Cancer experts often recommend that these patients avoid dietary supplements altogether.

Keep in mind that most of what you hear or read about dietary supplements is based on anecdotal evidence -- that is, evidence based on people's (even doctors') personal experiences or opinions rather than objective, controlled scientific studies.

Be skeptical of sources that make grand claims based on a few people's testimonials or vague references to "scientific proof." The rule "if it sounds too good to be true, it probably is" usually applies to such claims. Remember also that the makers and sellers of supplements have a vested interest in promoting their products. Look for evidence or research on the supplement from objective, third-party sources wherever possible.

Regardless of your treatment, it is always safest to talk with your doctor about the exact amount of each supplement you plan to take before starting on a supplement regimen.

Talking With Your Doctor

Many doctors are just starting to learn about the uses, risks, and potential benefits of dietary supplements. In some cases, this can widen the gap between patient and doctor when it comes to using supplements along with a mainstream treatment. This situation should improve as more studies are done and better information becomes available.

We encourage you to gather as much information as possible on the dietary supplement you are thinking about. Then, approach your doctor with the information you have, and ask for an open conversation. Ask for his or her professional opinion as to whether the treatment is safe and medically sound, and how it might be safely added to your cancer treatment.

The American Cancer Society has compiled the following basic information about choosing safe dietary supplements. If you are thinking about taking a dietary supplement, you may find the following information and suggestions helpful.

Common Misconceptions About Dietary Supplements

Megadosing: The "More Is Better" Myth

Many people wonder why dietary supplements such as vitamins, herbals, and botanicals are sold over the counter or without a prescription from a doctor, while medications (or drugs) are more closely regulated and controlled. People often make the mistake of assuming that because supplements are sold over the counter, sometimes with little or no direction on the label, they are completely safe to take, even in high doses. In the 1990s there was a trend of "megadosing" antioxidants such as vitamin C, beta carotene, and vitamin E. Even though no scientific studies have ever proven that large doses of vitamin C can prevent or cure colds, many people still think this is true. You may have heard a number of claims about the benefits of taking large doses of certain vitamins. But the practice of using large doses of vitamins to fight disease in humans is not supported by the available scientific evidence.

In fact, large doses of some vitamins or minerals can be dangerous and toxic. For example, too much vitamin C can interfere with the body's ability to absorb copper, a metal that is essential to our body chemistry. Also, too much phosphorous can inhibit the body's absorption of calcium. In addition, large doses of vitamins A, D, and K are not eliminated quickly by the body and can easily reach toxic levels when too much is taken. Talk with your doctor before taking large doses of any vitamin, mineral, or other supplement. Your nurse or pharmacist may also be able to give you more information on safe dosages. Even when vitamin doses are not high enough to cause toxic effects, the overall impact on health may be negative. For example, several large studies found that, on average, people taking vitamin E supplements lived no longer than those who didn't. Some even died sooner, particularly of heart failure.

The "Natural Is Safe" or "Natural Is Better" Myth

In today’s cultural climate, you will not find much support for the idea that a man-made or refined substance is better or safer than one sold in its unrefined, natural state. However, supplements that claim to be "all natural" are not always better or safer for people to take than refined or manufactured substances. Keep in mind that some of the most toxic substances in the world occur naturally. Poison mushrooms, for example, are completely natural but not safe or helpful to humans. Many plants in nature are toxic, even deadly, if taken internally.

Botanical supplements (such as garlic, ginger, ginkgo biloba, echinacea, and others) are made of plant material, so many of them are sold as "natural" products. However, plants are made up of many chemicals. Some of these chemicals can be helpful while others are poisonous or can cause allergies in humans. Botanicals that market themselves as "all natural" are not always the most helpful ones, since they re not refined to remove potentially harmful chemicals.

Botanicals can contain any or all parts of the plant, including roots, stems, flowers, leaves, pollen, and juices. Different parts of plants can have very different effects on humans. For example, dandelion root is a laxative (causes bowel movements), while dandelion leaves contain a diuretic (chemical that increases urination). If you decide to use a botanical supplement, make sure you know what parts of the plant were used in its production. If you are unsure, contact the company and ask about how they make their supplement.

Also, remember that safety and dose are related. The leaves or roots of some plants can be safely consumed in small amounts as an herb. But concentrated extracts sold as liquids or pills may contain the plant's chemicals in far greater amounts and may not be safe.

The "It's Been Used for Thousands of Years, So It Must Be Good" Myth

Knowing that a botanical has been used in folk or traditional medicine for thousands of years is helpful but is not convincing proof of safety. If small amounts of a plant caused painful or life-threatening side effects right away, its use is unlikely to have persisted in folk medicine or traditional medical systems. However, traditional medical systems of thousands or even hundreds of years ago did not have the scientific methods to detect long term side effects. So, if a plant seemed useful over the short term but actually increased the risk of chronic disease (like cancer, heart failure, or kidney failure) after years of use, those side effects would have not been noticed.

It is also important to find out whether a plant is being used now like it was in its traditional use. For example, tea prepared from a certain plant might have been safely used in traditional Chinese medicine to treat occasional bouts of asthma when given by an experienced practitioner. On the other hand, daily use of much higher doses taken in a concentrated form with no professional supervision might be quite unsafe.

The "It Can't Hurt to Take Supplements With my Regular Medicines" Myth

Many people also assume that dietary supplements can safely be taken along with any prescription drugs. This is also not true. For example, certain botanicals can block or speed up the body's absorption of some prescription drugs, causing the person to have too much or too little of the prescribed drug in their bloodstream. Most drug companies and producers of herbal supplements do not do research on possible drug interactions, so the risks of taking supplements with many medications are unknown.

Talk with your doctor about any herbal supplements you wish to take. He or she can tell you of any known interactions with medicines you may be taking. Unfortunately, there are always new drugs and supplements for which interactions have not yet been found. Talk with your doctor or pharmacist about the chance of interactions if you are taking newer drugs or supplements.

FDA Regulation of Drugs Versus Dietary Supplements

All over-the-counter and prescription drugs are regulated in the United States by the Food and Drug Administration (FDA). Because dietary supplements (including all forms of botanicals and vitamins) are not considered drugs, they are not put through the same strict safety and effectiveness requirements that other drugs are.

FDA Regulation of Drugs

Generally speaking, new drugs are considered by the FDA to be unsafe until they are proven safe by clinical trials. Clinical trials are tests done under well-controlled conditions on volunteer humans by experts, even on drugs sold over the counter (without a prescription.) The FDA must approve any new drug before it can be legally sold in the United States. This approval process requires that the drug undergo a series of several clinical trials. The clinical trials must show "substantial evidence" that the drug is both safe and effective for each of its intended uses.

Once the FDA approves the drug, it must be manufactured under carefully monitored conditions and packaged with complete information on the best dose, route, and schedule. The package information must include a listing of known side effects, contraindications (special conditions under which using the drug would cause too much risk), or unsafe interactions with other drugs. Once the general public is using a new drug, doctors are required to report to the FDA any ill effects their patients may experience. This data ensures that any side effects not seen in the clinical trials will eventually be found and kept track of for the safety of other people.

FDA Regulation of Dietary Supplements

In 1994, the Dietary Supplement Health and Education Act (DSHEA) defined dietary supplements as a category of food, and therefore under different regulations than drugs. They are considered safe until proven otherwise. Under the DSHEA, dietary supplements cannot contain any ingredients that may have "a significant or unreasonable risk of illness or injury" when the supplement is used as directed on the label, or under normal conditions of use if there are no directions on the label. If a dietary supplement contains a new ingredient, the manufacturer must provide the FDA with "adequate proof" that the ingredient is safe before the supplement is marketed to the public.

However, manufacturers are not required to test new ingredients or supplements in clinical trials, which would help find risks and potential interactions with drugs or other substances. The DSHEA gives the FDA permission to stop a company from making a dietary supplement, but only when the FDA proves that the product poses a significant risk to the health of Americans. They are found unsafe only after they cause harm. This approach is the reverse of the way over-the-counter and prescription medicines are treated.

Because dietary supplements are usually self-prescribed, there is no controlled system for reporting bad reactions. If a supplement has unknown side effects or interactions with other drugs, foods, or supplements, they are not likely to be discovered as quickly as those of new drugs on the market.

What Kinds of Problems Have There Been With Supplements and Herbs?

Since they became widely available in 1994, the FDA has found problems with some dietary supplements. Products such as herbs were sometimes contaminated with germs, pesticides, or toxic heavy metals. Others did not contain what was listed on the label at all. Still others contained more or less than the amount claimed on the label. Vitamin supplements, for example, were sometimes found to contain much less than the stated amounts on the labels. Some "herbal" supplements have been found to contain prescription drugs that were not listed on their labels. Some of these problems can cause serious health issues for the consumer.

How to Report Serious Adverse Reactions

If you or someone in your family suffers serious harm or illness as a result of supplement use, first call your doctor or other health care provider. After you have been treated, you or your doctor may report the adverse reaction to the FDA by calling 1-800-FDA-1088 or by going to the FDA's MedWatch Web site. The FDA considers an adverse event serious if it causes death, a life-threatening situation, admission to a hospital or a longer-than-expected hospital stay, permanent disability, a birth defect, or if it requires medical or surgical care to prevent permanent impairment or damage. When talking to the FDA, you will need to provide:

  • The name and telephone number of the person who got sick or had the problem; if that person cannot be reached, the FDA will need the name and number of another person who can give more information if needed 
  • A description of the problem and how it was addressed 
  • The name (including the brand or manufacturer) of the product.

In addition to the above required information, you will be asked about the age, weight, and sex of the person who had the problem. The FDA staff will ask when and how much of the supplement was taken, and for how long. They will want to know where and when the product was purchased, lot number, and expiration date if available. This information is generally not required, but if you can get it, it can greatly help them follow up on the problem.

In addition to reporting to the FDA, you should notify the manufacturer of the product (listed on the label) and the store, seller, or Internet vendor where you bought the product.

Manufacturing Guidelines for Dietary Supplements

Currently, there are no guidelines in place for the production of dietary supplements, although this should be improving over the next few years. It is generally the manufacturer's responsibility to see that the supplements they produce are standardized, quality products that meet the specifications described on their label. Many manufacturers follow careful, consistent production standards and market only high-quality, correctly labeled supplements. However, some less scrupulous manufacturers make supplements that contain little or none of the products listed on the label. Some supplements contain a larger dose than the label lists, possibly due to poor quality controls. There have even been reported cases of toxic products.

The Department of Health and Human Services has put out a set of standards (called Good Manufacturing Processes, or GMPs) for producing dietary supplements. Until the new standards go into effect, it may be hard to know whether the supplements contain what the label says they do.

How Will the New FDA Rules Affect Herbs and Supplements?

In June of 2007, the FDA announced plans for stronger requirements for companies that make dietary supplements. The FDA will require that dietary supplements follow standards called Good Manufacturing Practices, or GMPs. This means that dietary supplements must:

  • be produced in a quality manner 
  • not contain any contaminants or impurities 
  • be labeled with the actual ingredients in the product

The companies do not have to meet these requirements right away. Large companies have until June 2008, medium-sized companies until June 2009, and small companies have until June 2010 to comply with the new rules.

The companies will still sell their products in much the same manner as before. However, if companies are following the new rule, the supplements will be more likely to contain what is listed on the label. The new rule addresses the quality of manufacturing processes for dietary supplements and the accurate listing of their ingredients on the label. It is important to know what the new rule does not do.

  • The new rule will not limit consumers' access to dietary supplements. 
  • The rule does not address the safety of their ingredients. 
  • The rule does not address their effects on health as long as proper manufacturing techniques are used.

Even so, the improvements in quality and label accuracy will make supplements less likely to cause harm as long as these rules are followed.

It is important to remember that, like all laws, the new regulations will not stop manufacturers from selling supplements that are falsely labeled. It will be up to the FDA and other law enforcement groups to try and stop criminal manufacturers once they have been discovered. As quickly as some of these groups have been surfacing, that may be a challenge. See the ACS document Complementary and Alternative Methods for Cancer Management for more information on quackery and fraud.

The USP Standard

The U.S. Pharmacopeia (USP) is an independent organization dedicated to quality control for the strength, quality, and purity of pharmaceuticals. In 1997, the USP began publishing standards for dietary supplements. These standards focus on the strength, quality, purity, packaging, and labeling of dietary supplements and are updated yearly. The USP also does product testing and site visits for companies who join their program.

Makers of dietary supplements are not required by law to adhere to USP standards. Look for the USP notation indicating product compliance with USP standards on the packaging of any supplement you consider buying. The new FDA rule may not be as stringent as the USP standards, so companies that have used these standards before may continue to do so. You can still look for products that use USP standards. The label may have the initials USP after the name of the product, or note that it conforms to USP standards. Some companies have the initials "NF" for National Formulary on their labels (The National Formulary is allied with USP, and has standards that more specifically relate to herbs and botanicals.) Some supplements even have both initials.

Reading Dietary Supplement Labels

Before you buy a supplement, look at the label carefully. It is easy to misread the claims that are being made about the product. The manufacturers of dietary supplements are allowed to make 4 kinds of claims on the labels of their products: nutritional claims, claims of well being, health claims, and structure or function claims.

Nutritional claims: These are statements about the general effects dietary supplements, vitamins, and minerals have on diseases known to be caused by nutrient deficiency. For example, "vitamin C prevents scurvy." These claims do not need to be approved by the FDA. However, the label must also state how many cases of the disease occur in the US. Consumers must weigh the risk of getting the disease in the US against the potential risks of the supplement itself.

Claims of well being: These are just that-- statements such as "makes you feel better." These claims also do not require pre-approval by the FDA. (See the ACS document Complementary and Alternative Methods for Cancer Management for more information on these kinds of effects.)

Health claims: These are statements about known health benefits of certain compounds. For example, risk-reduction claims such as "folate may reduce the chance of pregnant women delivering an infant with neural tube defects" fall into this category. The FDA must pre-approve all health claims and requires that they be supported by evidence from scientific studies. Remember that risk-reduction claims are not the same as prevention claims.

Structure or function claims: These are the most hotly debated and confusing to consumers. They are claims about the effect of the dietary supplement on the structure or function of the body. The FDA published a ruling in January 2000 that explained exactly what kinds of structure or function claims would be acceptable for dietary supplements. Dietary supplements may not make any claims regarding the treatment of disease. However, the following product descriptions are acceptable as structure or function claims for dietary supplements:

  • The product's mechanism of action ("works as an antioxidant") 
  • The product's effects on cellular structure ("helps membrane stability") 
  • The product's effects on the body's physiology ("promotes normal urinary flow") 
  • The product's effects on chemical or laboratory parameters ("supports normal blood glucose") 
  • Claims of maintenance ("helps maintain a healthy circulatory system") 
  • Other non-disease claims ("helps you relax") 
  • Claims for common conditions and symptoms related to life stages ("reduces irritability, bloating, and cramping associated with premenstrual syndrome")

Structure or function claims are not reviewed by the FDA. In fact, labels that carry them must also include the disclaimer "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 FDA requires this disclaimer on supplement labels because it is easy for consumers to misunderstand structure or function claims. For example, many consumers believe that a statement such as "helps maintain vision acuity" means the product has been proven to prevent vision loss, or that a statement such as "helps maintain a healthy prostate gland" means the product has been proven to prevent or remove diseases such as prostate cancer. Do not assume that because a product claims to support or promote healthy body function that it prevents or reduces the risk of any disease, including cancer. Products that are proven to have a significant effect on any disease are considered drugs by the FDA and are strictly regulated as such.

Guidelines for Choosing Safe Dietary Supplement Products

  • First, speak with your doctor or other health care provider about any supplement you might consider taking. He or she can probably tell you if the supplement has any risks to your health and if the supplement is safe to take with other medications you may be taking. 
  • Find information on the product written by recognized medical experts or government agencies. Bring this information to your doctor's attention. You can start on the Web by visiting the National Institutes of Health’s Office of Dietary Supplements at http://dietary-supplements.info.nih.gov/ and clicking on "Health Information." 
  • When you shop for supplements, look for USP or NF on the package label. 
  • If you are shopping for a botanical, make sure to find a product that uses only the effective part of the plant. Avoid botanicals that have been made using the entire plant, unless the entire plant is recommended. 
  • Remember that a product described as "natural" is not necessarily safer or more effective. 
  • Consider the name and reputation of the manufacturer or distributor. Is it a nationally known name? Large companies with a reputation to uphold are more likely to manufacture their products under strict, quality-controlled conditions. 
  • Does the label provide a way to contact the company if you have questions or concerns about their product? Reputable manufacturers will provide contact information on the label or packaging of their products. 
  • Contact the manufacturer and ask about their quality control procedures and manufacturing processes. 
  • Try to avoid mixtures of many different supplements. The more ingredients, the greater the chances of harmful effects. 
  • Avoid supplements priced significantly lower than similar products; they are likely to be of lower quality. 
  • Avoid products that claim to be "miracle cures," "breakthroughs," or "new discoveries," to have benefits but no side effects, or to be based on a "secret ingredient" or method. Such claims are almost always fraudulent, and the product may contain potentially harmful substances or contaminants. 
  • Avoid products that claim to be effective treatment for a wide variety of unrelated illnesses. If a supplement claims that it can diagnose, treat, cure, or prevent disease, such as "cures cancer," the product is being sold illegally as a drug. 
  • Avoid products that claim to be safe or effective based solely on testimonials.

Additional Resources

More Information from Your American Cancer Society

We have selected some related information that may also be helpful to you. These materials may be ordered from our toll-free number.

Complementary and Alternative Methods for Cancer Management

Guidelines for Using Complementary and Alternative Methods

American Cancer Society Operational Statement on Complementary and Alternative Methods of Cancer Management

National Organizations and Web Sites

In addition to the American Cancer Society, other sources of patient information and support include:

National Institutes of Health
Office of Dietary Supplements
Telephone: (301) 435-2920
Internet Address: http://ods.od.nih.gov/

U.S. Department of Health and Human Services
Telephone: 1-877-696-6775
Internet Address: http://www.hhs.gov (click on "Drug & Food Information")

U.S. Pharmacopeia (USP)
Telephone: 1-800-227-8772
Internet Address: www.usp.org

U.S. Food and Drug Administration
Telephone: 1-888-INFO-FDA (1-888-463-6332)
Internet Address: www.fda.gov

Center for Food Safety and Applied Nutrition (CFSAN)
Telephone: 1-888-SAFEFOOD (1-888-723-3366)
Internet Address: www.cfsan.fda.gov

Telephone: 1-800-FDA-1088 (1-800-332-1088)
Internet Address: www.fda.gov/medwatch

*Inclusion on this list does not imply endorsement by the American Cancer Society

No matter who you are, we can help. Contact us anytime, day or night, for information and support. Call us at 1-800-ACS-2345 or visit www.cancer.org.


Kurtzweil P. An FDA Guide to Dietary Supplements. FDA Consumer; January 1999. Available at: http://www.cfsan.fda.gov/~dms/fdsupp.html. Accessed November 14, 2007.

Lai MW, Klein-Schwartz W, Rodgers Gc, et al. 2005 Annual Data Report of the American Association of Poison Control Centers. Available at: http://www.aapcc.org/annual.htm. Accessed November 14, 2007.

Office of Dietary Supplements, National Institutes of Health. Background about Claims and Labeling. Available at: http://dietary-supplements.info.nih.gov/Health_Information/Health_Information.aspx. Accessed November 14, 2007.

U.S. Food and Drug Administration, Center for Food Safety and Applied Nutrition. Dietary Supplement Current Good Manufacturing Practices (CGMPs) and Interim Final Rule (IFR) Facts. June 25, 2007. Available at: http://www.cfsan.fda.gov/~dms/dscgmps6.html. Accessed November 14, 2007.

U.S. Department of Health and Human Services, Office of the Inspector General. Adverse Event Reporting For Dietary Supplements: An Inadequate Safety Valve. April 2001. Available at: http://oig.hhs.gov/oei/reports/oei-01-00-00180.pdf. Accessed November 14, 2007.

U.S. Food and Drug Administration, Center for Food Safety and Applied Nutrition. Dietary Supplement Health and Education Act of 1994. December 1, 1995. Available at: http://www.cfsan.fda.gov/~dms/dietsupp.html, accessed November 15, 2007

U.S. Food and Drug Administration. Dietary Supplements. Overview. Available at: http://www.cfsan.fda.gov/~dms/supplmnt.html. Accessed November 14, 2007.

Revised: 12/06/2007

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