Taking Vitamins, Herbal Products, and Other Dietary Supplements During Cancer

Approved by the Cancer.Net Editorial Board, 03/2021

Many people take dietary supplements like vitamins or herbal products. People take supplements for different reasons, like wanting to improve health, get additional nutrition, boost the immune system, or treat side effects. These products are widely available for purchase without a prescription in the United States. But not all supplements are safe or effective, especially during cancer treatment.

Always talk with your cancer care team before taking a dietary supplement, even if it is one that you have taken in the past. Some dietary supplements, including herbal products, can interfere with your cancer treatment. Supplements can cause unwanted side effects or even reduce your treatment's effectiveness.

There are 2 main supplement categories:

Dietary products. These are vitamin and mineral products. Some of their characteristics include:

  • May come as pills, capsules, tablets, liquids, creams or powders.

  • Contain 1 or more ingredients, such as vitamins, minerals, herbs, enzymes, amino acids, and/or hormones.

  • Available in amounts (dose) that are lower than, equal to, or higher than the recommended daily levels for individual nutrients.

Herbal, botanical, and other "natural" products. The characteristics of these products include:

  • May come in tablets, capsules, powders, liquids, and tea leaves or tea bags.

  • Contain plants or parts of plants, algae, or fungi.

  • Other products in this category might contain extracts from animals, such as toad or snake venom.

How can I tell FDA-approved drugs and dietary supplements apart?

It is sometimes difficult for consumers to know if a specific supplement product is safe. Prescription and over-the-counter medications go through many scientific tests to make sure they are safe and effective before it can be sold in stores. In the United States, the Food and Drug Administration (FDA) then approves or rejects each medication. However, unlike medications, the FDA does not test or approve dietary supplements or herbal products.

Sometimes, it can be difficult to tell if a product is an FDA-approved drug or if it is a dietary supplement. They can be sold next to each other on a store shelf. The easiest way to tell is that FDA-approved drugs are required to carry a label that says "Drug Facts." The label on a dietary supplement will say "Supplement Facts."

How are dietary supplements regulated?

Many people take vitamins and supplements without a problem. But it is always important to talk to your health care team if you are taking or thinking about taking a supplement. Supplements carry risks and some have strong effects.

Unlike medication, the manufacturer and supplier of a dietary supplement are solely responsible for the ingredients, dose, and preparation of their product. These factors determine the safety and efficacy of the product. Because there is no regulation or oversight, these products may contain harmful ingredients, excess amounts of some ingredients, or less of an ingredient than they state on the label.

Manufacturers can also make claims about what their products do on labels. The FDA does not require proof that these claims are truthful. After a dietary or herbal product is on the market, the FDA can only claim it is unsafe after consumers report problems with it. The FDA offers a portal for reporting such problems on its website.

The most reliable source for whether a specific product is safe or effective for you is your doctor. Just because a product is labeled as "natural" does not mean it is harmless, safe, or okay to take during or after cancer treatment. Your doctor can help you determine whether a supplement is safe to take, particularly with your individual cancer treatment and during recovery.

What is the difference between complementary use and alternative use of supplements?

There is a major difference between using supplements during cancer as a "complementary therapy" or an "alternative therapy."

Complementary therapy. When people use a dietary or herbal supplement as a complementary therapy, it means they are using the product while receiving standard cancer treatment. For example, taking ginger to reduce nausea during chemotherapy.

Some products are safe when used as a complementary therapy for a specific purpose with a doctor's guidance. But there can be concerns about possible drug interactions, which are unwanted effects between 2 or more medications and/or supplements that have not been well researched. There are known interactions with different supplement products that can reduce the effectiveness of specific medications and other cancer treatments. See more information below.

Alternative therapy. When people use a dietary or herbal supplement as an alternative therapy, it means they are using the product to try to treat the cancer itself instead of receiving standard cancer treatment. For example, taking ginger to cure cancer instead of receiving chemotherapy. This is very dangerous. No dietary or other supplemental product can cure or treat cancer.

Can supplements be harmful for people with cancer?

People receiving cancer treatment must be very careful about using dietary and herbal products. Some of these products can interfere with different cancer treatments, including surgery, chemotherapy, and radiation therapy.

For example, supplements like garlic, ginkgo biloba, ginseng, and Vitamin E can increase risk for bleeding. This could be dangerous for patients undergoing or recovering from surgery. Supplements can also interfere with prescription and over-the-counter medications you are already taking. They may also be unsafe if you have specific health problems, including high blood pressure, diabetes, mental health conditions, heart disease, or blood clotting problems.

Supplements can cause serious side effects including:

  • High blood pressure

  • Nausea

  • Diarrhea

  • Constipation

  • Fainting

  • Headaches

  • Seizures

  • Heart attack

  • Stroke

Contact your doctor right away if you experience any harmful side effects.

How to use a supplement safely

It is possible to use some dietary and herbal supplements safely. In some places, complementary therapies are common along with cancer treatment. For example, traditional Chinese medicine often incorporates herbal therapies as a regular part of cancer treatment.

The most important thing is to do your research and talk to your doctor. Learn more about how to evaluate health information online. Here are some suggestions for what to know before you take any supplements:

  • Buy only single-ingredient products approved by your doctor. Some products contain other unlabeled herbs, pesticides, prescription drugs, heavy metals, or other substances.

  • Make sure the bottle clearly shows the dosage.

  • Look for a certification mark or seal from an independent, third-party organization. These include:

  • Check the label to see if researchers have tested the product. Contact the manufacturer for the test results. Talk with your doctor about anything that is not clear.

  • Be skeptical of claims on labels, particularly those that say the product will cure cancer. No single remedy or treatment can successfully treat all cancers. And no dietary or other supplement product can cure cancer.

How to start a conversation about supplements with your health care team

Deciding if, when, and how to use a dietary or natural product during cancer treatment can be difficult. After doing the research outlined above, talk to your health care team about any supplement products you would like to take. One professional who can provide information is an oncology pharmacist. Make sure to always:

  • Discuss your choice with your doctor.

  • Make sure they understand the reason why you want to use a supplement.

  • Ask about other, safer alternatives. For example, yoga or meditation is safer than a supplement for sleep problems and have been found effective.

Questions to ask your health care team before taking a supplement include the following:

  • What are the possible benefits and risks of taking this supplement, based on my medical history?

  • Could it interact with my cancer treatment? If so, how?

  • What are possible side effects of taking this supplement?

  • What dosage and how long can I take a supplement?

  • Is there any new information available about this supplement?

  • What are other options to help me with cancer side effects?

Related Resources

5 Things You Should Know About Herbs and Supplements

Evaluating Complementary and Alternative Therapies

Types of Complementary Therapies

Side Effects

More Information

Federal Trade Commission: Cancer Treatment Scams

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

National Center for Complementary and Integrative Health: Using Dietary Supplements Wisely

FDA: Tips For Dietary Supplement Users

FDA 101: Dietary Supplements

Natural Medicines Comprehensive Database