Demographic, medical, and behavioral characteristics associated with over the counter non-steroidal anti-inflammatory drug use in a population-based cohort: results from the Multi-Ethnic Study of Atherosclerosis

Background: Three types of non-steroidal anti-inflammatory drugs (NSAIDs) can be obtained both over the counter (OTC) and by prescription in the United States. OTC NSAID use is not recorded in prescription claims databases; this might lead to differential misclassification of NSAID exposure status in studies that use computerized pharmacy databases to study NSAID use.

Objective: To evaluate characteristics of OTC versus prescription NSAID users.

Methods: This analysis is set within the Multi-Ethnic Study of Atherosclerosis (MESA) study; a prospective cohort study of 6814 adults from four ethnic groups (European descent, Asian, African-American, and Hispanic) with a mean age of 62 years. The cohort was restricted to those who initiated NSAID use (aspirin, ibuprofen, or naproxen) during follow-up. We compared information about age, sex, ethnicity, body mass index, smoking, diabetes, medication use, education, income, health insurance status, and exercise between groups.

Results: OTC NSAID use was prevalent at baseline (25% aspirin, 9% ibuprofen, and 2% naproxen). Compared to prescribed NSAID use, OTC NSAID use was lower for users of non-European descent for all classes: aspirin (p < 0.0001), ibuprofen (p < 0.0001), and naproxen (p = 0.0094). For aspirin, differences were seen for male gender (relative risk (RR): 0.92; 95%confidence interval (CI): 0.86-0.98), use of lipid lowering drugs (RR: 0.88; 95%CI: 0.80-0.96), low income (RR: 0.89; 95%CI: 0.81-0.97), and participants one standard deviation above average in intentional exercise (RR: 1.03; 95%CI: 1.01-1.05).

Conclusions: OTC NSAID use is prevalent in an older multi-ethnic population and OTC users differ from prescription NSAID users. Caution should be exercised when using prescribed NSAIDs as a proxy for NSAID use.