**1. Introduction**

In 2018, prescription drug expenditures in the United States exceeded USD 335 billion (CDC 2021). Due to high prices, consumers from the United States often purchase brand name pharmaceutical products in Mexico (Dalstrom et al. 2020). Those purchases are transacted both in-person and online (Fullerton and Miranda 2011; Fullerton et al. 2014). Most research related to this form of cross-border medical tourism employs point-in-time cross-sectional data sets (Dalstrom et al. 2021).

This study examines an overlooked aspect of the online brand name medicine trade. Rather than examine price differences for a single point-in-time, this effort examines whether there is a dynamic relationship between online medicine prices in the two countries. It achieves this using a data set that monitors monthly prices for the top 50 online brand name medicines sold in Mexico and the United States (Fullerton and Fullerton 2022).
