Many low- and middle-income countries are currently undergoing a dramatic epidemiological transition, with an increasing disease burden due to degenerative noncommunicable diseases. Inexpensive medication treatment often represents a cost-effective means to prevent, control or cure many of these health conditions. Using micro-data from the 2001 Mexican Health and Aging Study, we assess horizontal inequity in medication treatment among older Mexicans before the introduction of Popular Health Insurance in Mexico. In doing so, we investigate the role of various dimensions of socioeconomic status for obtaining indicated medication treatment within a comparatively fragmented health-care system that features relatively high out-of-pocket expenditures. Our empirical analysis suggests health insurance coverage as a key socioeconomic determinant of indicated medication use with large and statistically significant positive effects on take-up. The effects of insurance status thereby clearly dominate any other possible effects of socioeconomic status on medication treatment. Our results thus highlight the importance of access to reliable health care and comprehensive coverage for rational medication use in the management of degenerative diseases. In light of this evidence, we expect that recent Mexican health-care reforms, which expand health insurance coverage to the previously uninsured population, will alleviate socioeconomic gradients in medication treatment among older people in need.