Self-medication is a common practice in many developing countries but little is known about its determinants. This study analyzes the factors that are associated with the use of self-medication in Mexico using the Mexican Health and Aging Study, a new nationally representative survey on adults aged 50 and over. We find that self-medication is related to socioeconomic status and the lack of access to professional healthcare. Our empirical results suggest that lack of government-sponsored health insurance coverage increases the propensity to self-medicate. A 10% increase in the proportion of adults with health insurance coverage could decrease the use of pharmacy consultations by .8% for public sector workers and by 1.7% for private sector workers. Increasing health insurance coverage could reduce the demand for self-medication by making healthcare more affordable and by changing the population perceptions about the benefits of modern medicine.