INTRODUCTION After many years of rapid increases, overdose death rates in the USA have begun decreasing, drawing considerable public attention [1-3]. The US overdose crisis has been characterized by a ‘four-wave’ paradigm, wherein an escalating death rate was attributed to shifting drug profiles over time [4-6]. The first wave entailed a surge in deaths involving commonly prescribed opioids [7]. Subsequently, in wave 2, drug overdose deaths involving heroin increased rapidly [8].