Introduction:
The prevalence of tobacco use has been commonly reported on a product by product basis; relatively few studies have estimated the prevalence of current dual and poly-tobacco use. This is the first study to systematically review the prevalence of current dual and poly-tobacco use among adults globally.

Methods:
We systematically searched Medline, Embase and Global Health for studies describing dual use and use of multiple tobacco products along with their synonyms. We included quantitative study designs with any measure of prevalence of current (past 30 day) dual tobacco (smoking tobacco plus one other tobacco product) and poly-tobacco use (concurrent use of more than two tobacco products) with focus on nationally representative samples of the adult populations worldwide.

Results:
In total, we found 19 studies yielding 329 prevalence estimates for single, dual and multiple tobacco products in 48 countries from 1998 to 2018. Definitions of dual and poly-tobacco use varied widely among the included studies. Dual use of smoking and smokeless tobacco was highest in South East Asia as well as in low and middle income countries. Russia had the highest prevalence of dual use (38.8% among adults). Prevalence of poly-tobacco use was highest in the European region, markedly in Denmark (11.9%), the UK (11.4%) and France (10.4%). There were multiple studies in the US, which suggest the proportion of poly-tobacco use has been increasing, even as the overall tobacco use declined in the past decade. The phenomenon is more pronounced in young adults.

Conclusions and applications:
To our best knowledge, this is the first study to systematically review the prevalence of dual and poly-tobacco use among adults, describing trends and patterns of poly-tobacco use globally. This information may inform policy makers and practice of tobacco control and provide support for effective regulation of alterative tobacco products.