Complementary and alternative medicine in cancer patients: characteristics of use and interactions with antineoplastic agents

Purpose Our objectives were to analyze the use of complementary and alternative medicine (CAM) in cancer patients and to describe the incidence and characteristics of interactions between CAM and antineoplastic agents. Methods We performed an observational study in cancer outpatients at a university hospital. Variables were collected through a 22-item questionnaire. Potential interactions between CAM and antineoplastic agents were analyzed using the Lexicomp ® , the About Herbs ® , and the summary of product characteristics. Mechanism of action, reliability, and the potential clinical effect of interactions were analyzed. Results The study population comprised 937 patients, of whom 65% used CAM (70.6% herbal products, 25.8% dietary supplements, and 3.6% homeopathy). Female sex, younger age, and breast cancer were associated with more frequent use of CAM. The primary source of information about CAM was friends and family (43.5%). A total of 335 (57.1%) patients did not tell their doctor that they took CAM. The five most common CAM were chamomile, green tea, pennyroyal mint, linden, and rooibos. At least one interaction between CAM and antineoplastic agents was reported by 65.0% of CAM users (33.9% of all patients). Depending on the mechanism of action, 80% of CAM diminished the metabolism of the antineoplastic agents. Conclusion Our results reveal a high incidence of interactions between CAM and antineoplastic agents. The most frequent CAM were herbal products. Family and friends were the primary sources of information that led patients to start taking CAM, and more than half of the patients did not tell their doctor that they were taking CAM.