Can Dietary Supplements Interfere with Cancer Treatment

Review of J Clin Oncol. 2004;22(12):2489-503.

A study in the Journal of Clinical Oncology looked at the 15 best-selling herbal remedies that are used in the United States today. The researchers studied whether or not these remedies are likely to interact with medications that are used to treat cancer. This study suggests that of the 15 most popular herbal remedies in the United States, nine may pose a risk of negative interactions with specific anti-cancer medications, including the popular remedies echinacea, ginseng and St John's wort. We discuss which herbs pose the greatest concern when it comes to interactions with cancer medications. We provide PRACTICAL information on what these findings mean, including a discussion of some of the weaknesses of this research. Along with talking to the medical care team about dietary supplement use, taking time to learn more about which common herbs can interact with cancer treatments will help people who are diagnosed with cancer to make more informed choices about their own health care.

Note: Numbers appearing at the end of sentences indicate research references. References are listed at the end of each article.

Background

Surveys tell us that one-third of adults in the United States use complementary and alternative medicine (CAM), including herbs, on a regular basis (1-3). Using CAM is even more common among people who are being treated for cancer. Studies tell us that up to 80% of people with cancer use CAM and up to 63% take herbal remedies (4,5). Many health experts worry that some of these herbs may interact with other medications. This is a particular concern for people who are being treated for cancer because many cancer medications have a very small 'window' in which they work. In other words, you have to have just the right amount of these medications in your body in order for them to fight the cancer most effectively. Having too much can cause toxic reactions. Having not enough means that the cancer is not being treated effectively.

A study in the Journal of Clinical Oncology looked at the 15 best-selling herbs that are used in the United States today to try to determine whether or not these remedies are likely to interact with cancer medications (6). It is hoped that this type of research will help us understand which dietary supplements and herbs may interact with different types of medications, so that these products can be used more safely in the future.

What The Researchers Studied

For this study, the researchers looked at 15 top-selling herbs in the United States for the year 2002. These top selling herbs are:

Herbal Remedy	Rank Based on Sales	Typically Used To Treat
Garlic	1	High Cholesterol
Ginkgo	2	Memory Loss/Dementia
Echinacea	3	Infection Prevention (e.g. common cold)
Soy Supplements*	4	Menopause Symptoms
Saw Palmetto	5	Enlarged Prostate
Ginseng	6	Physical & Mental Fatigue
St. John's Wort	7	Mild Depression
Black Cohosh	8	Menopause Symptoms
Cranberry	9	Bladder Infections
Valerian	10	Insomnia & Stress
Milk Thistle	11	Liver problems due to hepatitis & alcohol use
Evening primrose	12	Premenstrual Syndrome (PMS)
Kava	13	Anxiety
Bilberry	14	Loss of Eyesight Due to Diabetes
Grape Seed	15	Allergies (e.g. hay fever)

*This refers to soy supplements, not whole soy foods.

Researchers used all of the detailed information that has been published on how these products work in our bodies to study whether or not they are likely to interact with different cancer medications. One way to understand how this works is to think about how the body actually uses and then excretes or 'gets rid of' different medications.

Think of the cells in your body as containing little chemical systems. The body uses many different 'chemical systems' to process medications. You can think of these systems as 'medication processing factories'. These factories allow your body to excrete or 'get rid of' the medications once they have done their job. This is necessary so that the medications don't build up to toxic levels in your body.

Now, here is the tricky part. Sometimes, the medications that you take AND herbs that you take are processed by the same factory. If this is true, this can affect how both the medication and the herb work.

Medications May Not Work Properly

A medication that you use and an herb can interfere with each other. If this happens, your medications may not do what they should do to fight your cancer. Also, your medications may not do what they should do to manage your symptoms.

Medications  May Be Processed Too Quickly

The medication might be processed more quickly than normal because of the herb. If this happens, you may not have enough of your medication in your body to do the job of fighting your cancer.

Medications May Be Processed Too Slowly

The medication might be processed more slowly than normal because of the herb. If this happens, you may end up with too much medication in your body. This could be toxic or cause damage to your liver or other organs.

Other Concerns

In addition to interfering with how medications are processed, it is possible that herbs can change how your body absorbs and transports (moves around) the medications from place to place in the body. This also can result in problems so that the medications cannot do their job properly.

Interactions between different substances in the body can be very complex, but from the few examples above, you can see how this issue is very important, especially for people who are being treated for cancer.

What The Study Found

After reviewing all of the information that is available on how the different cancer medications and the different herbs work in the body, the researchers reached some conclusions.

Of the 15 top selling herbs in the United States, 9 of them may have problems by interacting negatively with certain cancer medications. The following table summarizes the information on which herbs may interact with different types of cancer medications. The names of the cancer medications are long and complex. Often, one drug will be called several different names. If you are unsure about the names of your cancer medications, please ask your doctor for clarification.

Herb	AVOID Taking With The Following Cancer Medications*	May Interact Negatively With The Following Cancer Medications
Garlic	Decarbazine	Use with caution with other types of chemotherapy; research is inconclusive
Gingko	Alkylating Agents; Antitumor Antibiotics; Platinum Analogues	Use caution with Camptothecins, Cyclophosphamide, EGFR-TK inhibitors, Epipodophyllotoxins, Taxanes, and Vinca Alkaloids; research is inconclusive
Echinacea	Campothecins; Cyclophosphamide; EGFR-TK inhibitors; Epipodophyllotoxins; Taxanes; Vinca Alkaloids	None listed
Soy Supplements**	Tamoxifen; Avoid in women with estrogen positive breast cancer or endometrial cancer	None listed
Ginseng	Avoid in women with estrogen positive breast cancer or endometrial cancer	Use caution with Camptothecins, Cyclophosphamide, EGFR-TK inhibitors, Epipodophyllotoxins, Taxanes, and Vinca Alkaloids; research is inconclusive
St. John's Wort	Avoid with ALL types of chemotherapy; St John's Wort interacts with multiple medications through many different pathways	Avoid with ALL types of chemotherapy
Valerian	None listed	Use caution with Tamoxifen, Cyclophosphamide and Teniposide; research is inconclusive
Kava	Avoid if you have liver disease; do not take with cancer drugs that are toxic to the liver	Use caution with Camptothecins, Cyclophosphamide, EGFR-TK inhibitors, Epipodophyllotoxins, Taxanes, and Vinca Alkaloids; research is inconclusive
Grape Seed	None listed	Use caution with Camptothecins, Cyclophosphamide, EGFR-TK inhibitors, Epipodophyllotoxins, Taxanes, Vinca Alkaloids, Alkylating Agents, Antitumor Antibiotics and Platinum Analogues; research is inconclusive

*The same drug may be called by several different names. If you are unsure about the names of your cancer medications, please ask your doctor for clarification.

**This refers to soy supplements, not whole soy foods.

Other Herbs

The researchers determined that for the remaining herbs, significant interactions with medications used to treat cancer are not likely to occur. This includes Saw Palmetto, Black Cohosh, Cranberry, Milk Thistle, Evening Primrose, and Bilberry.

What do these results mean?

Based on the research that is available today, this study tells us that some popular herbs may interact negatively if taken with medications that are used to treat cancer. This is important to keep in mind if you are currently undergoing treatment for cancer.

This research review does have some weaknesses. Some of the interactions are not proven, they are just suspected to be problems. Researchers may have incomplete information on how a particular herb works in the body. They may come up with a 'best guess' as to whether or not a certain herb will interact negatively with a particular medication. Sometimes, further studies will prove that a particular herb and drug do not interact negatively, even though early research suggested they could.

Sometimes researchers will look at how a drug and an herb interact in a cell study. This type of study might show a big problem with interaction. However, when these same products are tested in people, it doesn't turn out to be a problem. A good example of this occurred with the herb Milk Thistle. Studies in cells suggested that Milk Thistle would interact negatively with certain medications that are used to treat HIV and AIDS. Further research in people showed that this was not a problem after all (7,8)

Finally, even though a particular herb may be suspected to interact negatively with cancer medications, the herb may be important because it can help fight in other ways. One example of this relates to the herb Ginseng. Even though some research shows that Ginseng might interact negatively with some cancer medications, other research shows that Ginseng can help fight cancer (9-11).

Using Herbs Safely

One important thing to keep in mind is that if you are taking medications to treat cancer, talk to your health care team about ALL other medications, dietary supplements, herbs, vitamins, and minerals. Do not take the advice of a health store clerk, a well-meaning friend or neighbor, or anyone who isn't a qualified health care provider.

Start by using the information discovered in this study to make some decisions about common herbs that you might be taking. If an herb that you are using is known to have an interaction with a cancer medication you are taking, you should not take these products together!

Other Herbs

Unfortunately, there are no black and white answers when it comes to mixing herbs and medicines. We've discussed the research on some of the more common herbs, but what if you are interested in other products that have not been reviewed? 

If you want to use herbal remedies, the most important thing you can do to look out for your own health and safety is to talk to your medical care team about this issue. If you want to use herbs and other dietary supplements, find a health care practitioner who can help you decide whether a certain product is right for you.

Because this area is gray, with a lot of 'maybes' and 'what ifs', the single most important thing you can do to help yourself is to be informed. Based on the research that is available right now, your health care provider may not be able to give you a 'yes' or 'no' answer on whether a specific herb is right for you. But, this person can help you weigh the positive and negative aspects of these products so that when you make a decision, you know that you are fully informed.

There is a lot of research available on how herbs and medications are processed in the body, but sometimes it's pretty hard to find! If you can't find the information you need to make an informed choice, ask your health care provider to help you find it. And once you are empowered with this information, you can make a choice that is right for you.

References

1. Klepser TB, Doucette WR, Horton MR, Buys LM, Ernst ME, Ford JK, Hoehns JD, Kautzman HA, Logemann CD, Swegle JM, Ritho M, Klepser ME. Assessment of patients' perceptions and beliefs regarding herbal therapies. Pharmacotherapy. 2000;20(1):83-87.

2. Eisenberg DM, Davis RB, Ettner SL, Appel S, Wilkey S, Van Rompay M, Kessler RC. Trends in alternative medicine use in the United States, 1990-1997: results of a follow-up national survey. JAMA. 1998;280(18):1569-75. 

3. Jonas WB. Alternative medicine - learning from the past, examining the present, advancing to the future.
JAMA. 1998;280(18):1616-18.

4. Richardson MA, Sanders T, Palmer JL, Greisinger A, Singletary SE. Complementary/alternative medicine use in a comprehensive cancer center and the implications for oncology. J Clin Oncol. 2000;18(13):2505-14.

5. Nam RK, Fleshner N, Rakovitch E, Klotz L, Trachtenberg J, Choo R, Morton G, Danjoux C. Prevalence and patterns of the use of complementary therapies among prostate cancer patients: an epidemiological analysis. J Urol. 1999 May;161(5):1521-24.

6. Sparreboom A, Cox MC, Acharya MR, Figg WD. Herbal remedies in the United States: potential adverse interactions with anticancer agents. J Clin Oncol. 2004;22(12):2489-503.

7. DiCenzo R, Shelton M, Jordan K, Koval C, Forrest A, Reichman R, Morse G. Coadministration of milk thistle and indinavir in healthy subjects. Pharmacotherapy. 2003;23(7):866-70.

8. Piscitelli SC, Formentini E, Burstein AH, Alfaro R, Jagannatha S, Falloon J. Effect of milk thistle on the pharmacokinetics of indinavir in healthy volunteers.
Pharmacotherapy. 2002;22(5):551-56.

9. Suh SO, Kroh M, Kim NR, Joh YG, Cho MY. Effects of red ginseng upon postoperative immunity and survival in patients with stage III gastric cancer. Am J Chin Med. 2002;30(4):483-94.

10. Yun TK, Choi SY, Yun HY. Epidemiological study on cancer prevention by ginseng: are all kinds of cancers preventable by ginseng? J Korean Med Sci. 2001;16(Suppl):S19-27. 

11. Yun TK, Choi SY. Preventive effect of ginseng intake against various human cancers: a case-control study on 1987 pairs. Cancer Epidemiol Biomarkers Prev. 1995;4(4):401-408.

Publish Date: 08/2004