Interactions between alternative and conventional medicines might be more frequent than previously thought

Many cancer patients use some form of alternative therapy. Most of them combine it with conventional oncological treatments which begs the important question whether the two can interact.

The aim of this new investigation was firstly to assess prevalence of interactions between alternative medicines (AMs) and drugs for comorbidities from a large survey on melanoma patients and secondly to classify herb-drug interactions with regard to their potential to harm. Consecutive melanoma outpatients of seven skin cancer centers in Germany were asked to complete a standardized questionnaire including questions about their AM-use and their taken medication for comorbidities and cancer. Each combination of conventional drugs and AMs 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 AMs. Risk evaluation for interaction was possible for 180 AM 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 drugs and AMs. Almost all patients using Chinese herbs were at risk (88.6 %).

The authors concluded that with a high rate of AM usage at risk of interactions between AMs and drugs taken for comorbidities, implementation of a regular assessment of AM usage and drugs for comorbidities is mandatory in cancer care.

On this blog, I have mentioned this problem repeatedly. For instance, I reported about a survey of 1,500 members of the German non-medically trained practitioner (NMP) associations. Its results showed that the treatments employed by NMPs were heterogeneous. Homeopathy was used by 45% of the NMPs, and 10% believed it to be a treatment directly against cancer. Herbal therapy, vitamins, orthomolecular medicine, ordinal therapy, mistletoe preparations, acupuncture, and cancer diets were used by more than 10% of the NMPs. None of the treatments were discussed with the respective physician on a regular basis. The authors concluded from these findings that many therapies provided by NMPs are biologically based and therefore may interfere with conventional cancer therapy. Thus, patients are at risk of interactions, especially as most NMPs do not adjust their therapies to those of the oncologist. Moreover, risks may arise from these CAM methods as NMPs partly believe them to be useful anticancer treatments. This may lead to the delay or even omission of effective therapies.

One problem regarding herb-drug interactions is that we currently have to rely more on speculations than on facts. The only exception is the issue of interactions with St John’s Wort (SJW). Some time ago, I reported on this blog about a study assessing how often SJW is prescribed with medications that interact dangerously with it. The researchers conducted a retrospective analysis of nationally representative data from the National Ambulatory Medical Care Survey. Twenty-eight percent of SJW visits involved a drug that has a potentially dangerous interaction with SJW. These included selective serotonin reuptake inhibitors, benzodiazepines, warfarin, statins, verapamil, digoxin, and oral contraceptives. The authors concluded that SJW is frequently used in potentially dangerous combinations. Physicians should be aware of these common interactions and warn patients appropriately.

My conclusion at the time is as true and important today: physicians ought to know about the potential of herbal remedies to interact with drugs but, considering the frequency of self-prescription of such treatments, raising  consumers’ awareness of the risks associated with herbal medicines is at least as important.