Cancer patients at risk of herb/food supplement-drug interactions: a systematic review.

Herbal medicines and dietary supplements are commonly taken by patients with cancer, leading to concern over interactions with conventional medicines. A literature search was carried out to identify published studies exploring supplement use by patients with a cancer diagnosis. A total of 818 articles were retrieved using the key words, but only 41 are judged to be relevant based on title. Following the review of the abstracts, ten papers were considered to be potentially relevant, but of these, only two met the selection criteria, and three additional papers were identified from published reviews. Of 806 patients surveyed, 433 (53.7%) were reported to be taking combinations of supplements and drugs, and 167 incidents of risk were identified, affecting 60 patients (13.9%). The interactions identified were mainly theoretical and not supported by clinical data. No studies reported any adverse events associated with these combinations; most did not record the actual drug combinations taken, and the risk potential of some supplements appears to have been over-estimated. More effort should be made to investigate supplement use in this vulnerable patient group, based on sound evidence of plausible interaction, not only to avoid harm but also to provide reassurance where appropriate if the patient wishes to take a particular supplement.