The benefits of drinking tea have been recognized for thousands of years. But did you know that some teas can interact with the breast cancer drug tamoxifen (sold under the brand name Soltamox)? A MyBCTeam member was surprised by this, saying, “I was not aware of herbal teas being an issue with this medication.”

You may be wondering if it’s safe to continue drinking your favorite brew if you take tamoxifen. Continue reading to learn more about how the drug can interact with the compounds found in tea.

How Can Tamoxifen Interact With Tea?

Tamoxifen is a hormonal therapy used to treat or prevent breast cancer. It works by blocking the effect of estrogen on breast cancer cells. For tamoxifen to be effective, your liver must first convert it into its active metabolite (active form) — endoxifen. Any food, drink, or drug that interferes with this process could limit the effectiveness of tamoxifen.

A group of proteins in your liver called cytochrome P450 enzymes (or CYP enzymes) are responsible for activating tamoxifen and for breaking it down into a form that’s easier for your body to get rid of. Several subgroups of CYP enzymes are involved in processing tamoxifen. Of these, CYP2D6 is primarily responsible for converting tamoxifen to endoxifen. Another CYP enzyme subgroup called CYP3A4 may also play a significant role.

Most research about tamoxifen interactions focuses on the effects of CYP2D6. Substances that interfere with CYP2D6 can block the enzyme from activating tamoxifen. This could mean it may not work as well to treat or prevent breast cancer.

Other substances are inducers of CYP enzymes that speed up how fast tamoxifen is metabolized. If your body gets rid of the drug too quickly, it may be less effective.

Although there isn’t much research about how different types of tea interact with tamoxifen, we can use our knowledge about how the compounds found in tea affect CYP enzymes to identify potential interactions.

Chamomile Tea

Chamomile is a common ingredient in herbal tea. Chamomile is promoted with claims of several health benefits, including:

• Improving sleep
• Reducing anxiety
• Relieving stomach upset
• Decreasing inflammation in the body

There aren’t many clinical studies that prove these benefits of chamomile. However, there is some evidence that it might help improve sleep and decrease anxiety.

The most common side effect of chamomile is an allergic reaction. Chamomile is in the same family of plants as ragweed, so if you have an allergy, you should avoid it.

Chamomile Tea and Tamoxifen

Even though chamomile is generally considered safe, there’s some evidence that it could have an interaction with tamoxifen. Laboratory studies have found that chamomile essential oil can inhibit CYP3A4 and CYP2D6. If these enzymes are inhibited, it means that your liver will have a harder time converting tamoxifen into its active form, possibly making it less effective.

These studies were not specifically on chamomile and tamoxifen. More research is needed to find out if the inhibitory effect of chamomile could impact breast cancer treatment in the real world.

Talk to your cancer care team or a registered dietician to find out if you can add chamomile to your diet.

Green Tea

Green tea is the most popular beverage in the world, other than water. A MyBCTeam member commented, “I have green tea daily.”

When consumed as a beverage or supplement, green tea’s potential health benefits include:

• Increased alertness
• Headache relief
• Some protection against high blood pressure

Many of green tea’s benefits are attributed to the antioxidant properties of polyphenols found in the tea. Antioxidants can prevent the formation of free radical molecules, which cause cell damage and inflammation to your tissues. Some researchers theorize that by preventing damage and inflammation from free radicals, green tea could have protective effects against cancer and heart disease.

There’s also some early evidence that drinking green tea might improve your prognosis (outlook) for breast cancer. However, it’s important to know that the National Cancer Institute does not recommend for or against using green tea to lower the risk of any type of cancer.

Drinking up to 8 cups (about 64 ounces) of green tea a day is considered safe. You should keep in mind that green tea contains caffeine, which may not be stated on the label. Liver problems have been reported in people who’ve taken green tea in pill form as a supplement.

Green Tea and Tamoxifen

A small 2020 study found that green tea didn’t affect the levels of endoxifen for 14 people with cancer taking tamoxifen. More research is needed, but early evidence suggests green tea likely doesn’t decrease the efficacy of tamoxifen.

Laboratory studies on mice and on human cells have found that the combination of green tea extract and tamoxifen might stop the growth of estrogen receptor-positive breast cancer cells.

Another animal study found that, when given at the same time as tamoxifen, one of the compounds found in green tea — called epigallocatechin-3-gallate (EGCG) — increased the amount of tamoxifen available in the body. EGCG might also prevent cancer cells from becoming resistant to tamoxifen. However, until higher-quality research in humans is done, scientists cannot confirm any of these possible benefits.

Ginger

Ginger is a spice that comes from the rhizome (underground stem) of the ginger plant. It’s been used for thousands of years to treat different types of nausea and vomiting. It has been studied to treat nausea due to:

• Pregnancy
• Motion sickness
• Chemotherapy
• Surgery

Several clinical trials have found that ginger is effective in relieving nausea and vomiting caused by chemotherapy for breast cancer treatment.

Ginger has been used safely in many clinical trials. The most common side effects include:

• Stomach discomfort
• Heartburn
• Diarrhea
• Mouth or throat irritation

Ginger can affect how your platelets function and make it harder for your blood to clot. If you’re taking a ginger supplement, you may need to stop taking it before you have surgery.

Ginger and Tamoxifen

Laboratory studies have found that some compounds in ginger root might inhibit CYP2D6 and CYP3A4. Theoretically, this could decrease the efficacy of tamoxifen. However, it’s unknown how ginger will affect your risk of breast cancer if taken with tamoxifen.

Other Foods and Supplements That Can Interact With Tamoxifen

In recent years, there’s been increased research on the effect of complementary and alternative medicines, like teas, on cancer and other medical conditions. However, just because something is natural doesn’t mean it’s safe. So far, there isn’t any evidence that a dietary supplement can treat or prevent cancer.

Other foods and dietary supplements that might decrease the efficacy of tamoxifen in some people include:

• Grapefruit
• Tangerines
• Alcohol
• Turmeric (curcumin)
• Black cohosh
• St. John’s wort
• Ginseng

Talk to your oncologist or a registered dietitian about which foods and drinks to eat or avoid while you’re taking tamoxifen.

Talk With Others Who Understand

MyBCTeam is the social network for people with breast cancer and their loved ones. On MyBCTeam, more than 64,000 members come together to ask questions, give advice, and share their stories with others who understand life with breast cancer.

How does taking tamoxifen affect your food and beverage choices? Share your experiences in the comments below, or start a conversation by posting on your Activities page.