implications remain research questions of considerable interest. Figure 1 provides an overview of these various mechanisms - we discuss (a) the epidemiology of lifetime co-occurrence of cannabis and tobacco use; (b) the mechanisms underlying lifetime co-occurring use, including shared genetic and environmental factors and economic factors; (c) route of administration as a contributing factor; (d) respiratory complications associated with co-occurring use; (e) overlapping withdrawal features; and (f) treatment approaches for smokers with cannabis problems and cannabis users with nicotine dependence.
