Some patients use dietary supplements and medicines concomitantly, with an inappropriate perception of their safety and efficacy. To clarify the perception between dietary supplement and medicine users and non-users, we conducted an internet survey. In this survey, 38.9% of participants used dietary supplements, 32.6% used prescription medicines, and 14.7% used dietary supplements and prescription medicines concomitantly. Then, we conducted a further survey on four groups, dietary supplement and prescription medicine users, dietary supplement only users, prescription medicine only users, and non-users (500 each). Dietary supplement users had favorable outcomes in terms of both the safety and efficacy of dietary supplements compared to dietary supplement non-users. This perception of dietary supplements was independent from medicine use. The awareness of the Health Food Network consumer navigation site, which provides information about dietary supplements for consumers, was the highest among dietary supplement and prescription medicine users, but it was still low (2.2%). In conclusion, consumers who use dietary supplement and prescription medicine concomitantly have favorable outcomes for their safety and efficacy and a low awareness of their interaction. There is a need to provide information, especially regarding the risk of interaction, that takes into account the consumer's situation.
