Can Supplements Interfere With Chemotherapy Treatment?

Although quite common, people who use herbs and supplements during and after chemotherapy are at risk for potentially serious medication interactions. That’s the conclusion of a recent study. Yet this risk appears to be largely unknown to patients.

“Surprisingly, most patients are not worried about potential medication interactions when they take herbs and supplements,” says Santash Rao, MD, Medical Director of Integrative Oncology for University Hospitals Connor Whole Health. “Yet, more than 88 percent of the patients in the study taking herbs and supplements were at risk for a major medication interactions, and nearly one-third of all herb and supplement interactions were rated as major.

Supplements and Vitamins Pose a Risk

The study conducted telephone surveys with 67 breast cancer and prostate cancer patients who had recently finished chemotherapy at two large medical centers.

Patients were asked questions about all medications they’d taken, including herbs and supplements, before, during and after chemotherapy. The research team then used this information and the patients’ medical records to analyze potential medication interactions.

The findings:

• About 84 percent of patients in the study reported using herbs and supplements, with use increasing after chemotherapy was complete.
• Four out of five patients who used herbs and supplements were at risk for a major medication interaction.
• When comparing patients who used herbs and supplements with those who didn’t, the researchers found that users were more likely to be at risk for a major medication interaction than non-users (92 percent vs. 70 percent).
• Nearly half of the potential medication interactions during a patient’s course of chemotherapy were rated as major.
• Interestingly, the most common herbs and supplements flagged for potentially severe medication interactions were vitamins such as multivitamins, vitamin D, vitamin E, vitamin C and magnesium, many of which are commonly used. Glucosamine was also included in this list.
• When asked if there were concerns about side effects or drug interactions with their use of herbs and supplements, 79 percent of cancer patients in the study responded ‘no.’

Discuss Supplements with Your Doctor

Dr. Rao says he hopes this small exploratory study will lead both oncologists and primary care providers to thoroughly discuss the potential interactions associated with herbs and supplements. The period during and after chemotherapy is especially critical, he says.

“With the highest risk of herb and supplement-related medication interactions occurring after chemotherapy, oncologists should ask about herbs and supplement use not only during treatment, but also after as patients move into survivorship care,” Dr. Rao says.

He hopes, too, that cancer patients will think twice and get good medical advice before taking herbs and supplements that may interfere with their treatment. In the study, the majority of patients were open to receiving advice from their medical team about herbs and supplements, and would stop taking them if they were told of a potential interaction.

However, Dr. Rao notes that many medication interactions are common and allowed if they improve a patient’s care. In addition, many herb-drug interactions have not been studied specifically. Rather, they are hypothetical based on what we know about chemical reactions in the body.

“Discussions about herbs and supplements by physicians may provide an opportunity to both prevent potential harms and strengthen the doctor-patient relationship. It’s important to guide people in decisions about what is safe to use, especially during active treatment with chemotherapy,” Dr. Rao says.

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