Risk of interactions between complementary and alternative medicine and medication for comorbidities in patients with melanoma

Complementary and alternative medicine (CAM) is used widely among cancer patients. Beside the risk of interaction with cancer therapies, interactions with treatment for comorbidities are an underestimated problem. The aim of this study was to assess prevalence of interactions between CAM and drugs for comorbidities from a large CAM usage survey on melanoma patients and to classify herb–drug interactions with regard to their potential to harm. Consecutive melanoma outpatients of seven skin cancer centers were asked to complete a standardized CAM questionnaire including questions to their CAM use and their taken medication for comorbidities and cancer. Each combination of conventional drugs and complementary substances was evaluated for their potential of interaction. 1089 questionnaires were eligible for evaluation. From these, 61.6 % of patients reported taking drugs regularly from which 34.4 % used biological-based CAM methods. Risk evaluation for interaction was possible for 180 CAM users who listed the names or substances they took for comorbidities. From those patients, we found 37.2 % at risk of interaction of their co-consumption of conventional and complementary drugs. Almost all patients using Chinese herbs were at risk (88.6 %). With a high rate of CAM usage at risk of interactions between CAM drugs and drugs taken for comorbidities, implementation of a regular assessment of CAM usage and drugs for comorbidities is mandatory in cancer care.