Background: We examined the patterns of nonvitamin dietary supplement (NVDS) use among adult prescription medication users in the United States. Methods: Using the 2002 National Health Interview Survey, we analyzed factors associated with NVDS use and prescription medication use in the prior 12 months with descriptive, χ2, and logistic regression analysis. Results: In the United States, 21% of adult prescription medication users reported using NVDSs in the prior 12 months. Of the respondents who used both prescription medications and NVDSs in the prior 12 months, 69% did not discuss this use with a conventional medical practitioner. Among adults who used prescription medications in the prior 12 months, the most commonly used supplements included echinacea, ginseng, ginkgo, garlic, and glucosamine chondroitin. Prescription medication users with menopause and chronic gastrointestinal disorders had the highest rates of NVDS use (33% and 28%, respectively), and prescription medication users with coronary heart disease and history of myocardial infarction had the lowest rates of use (12% each). In the adjusted analysis, factors associated with increased use of NVDSs by prescription medication users included being female, being Hispanic, having more years of education, living in the West, lacking medical insurance, and having chronic conditions. Elderly respondents were less likely to use NVDSs. Conclusion: One in 4 prescription medication users took an NVDS in the prior 12 months, yet the majority did not share this with a conventional medical professional.