Potential interactions between complementary/alternative products and conventional medicines in a Medicare population.

Background: Despite the high prevalence of complementary and alternative medicine (CAM) product use among the elderly, little is known about the extent of concurrent CAM-conventional medicine use and the potential for adverse reactions.

Objective: To determine the prevalence of CAM product use concurrent with conventional medications, prescription and nonprescription, in a Medicare population and assess the risk for adverse interactions.

Methods: Retrospective analysis was performed on Cardiovascular Health Study interview data from 1994, 1995, 1997, and 1999. The prevalence of concurrent combinations of CAM products and conventional drugs was tabulated. The adverse interaction risks were categorized as unknown, theoretical, and significant.

Results: Of 5052 participants, the median age was 75, 60.2% were female, 16.6% were African American, and 83.4% were white. The percent using CAM products during the 4 time periods was 6.3%, 6.7%, 12.8%, and 15.1%. The percent using both CAM products and conventional drugs was 6.0%, 6.2%, 11.7%, and 14.4%. Of these, 294 (5.8%) individuals took combinations considered to have a significant risk for an adverse interaction. Combinations with risk were observed on 393 separate interviews. Most (379) involved a risk of bleeding due to use of ginkgo, garlic, or ginseng together with aspirin, warfarin, ticlopidine, or pentoxifylline. An additional 786 observations of combinations were considered to have some, albeit theoretical or uncertain, risk for an adverse interaction.

Conclusions: Concurrent use of CAM products and conventional medicines in a Medicare population was found to be common. Research to define the risks of combining ginkgo and garlic supplements with aspirin should be of high priority.