Actually, later in their paper they say: "Although we have argued for a causal role for smoking in generating these patterns, the growing mortality gaps still seem too large and the causes of death too varied to blame the patterns on the adverse health effects of tobacco use alone. As noted above, smoking is likely to play a role in amplifying the impact of other factors adversely affecting midlife mortality, such as the marketing efforts by opioid manufacturers targeted to areas with high rates of smoking-related illness, coupled with epigenetic changes making smokers more susceptible to opioid use disorders. Still, the strength of our findings that smoking is predictive of spatial trends in midlife mortality points towards different mechanisms needed to explain the troubling trends that have unfolded since 1990."