Background:
The Framework Convention on Tobacco Control (FCTC) addresses a wide range of issues including protection from exposure to secondhand smoke and advertising, promotion and sponsorship. The FCTC represents a minimum set of tobacco control policies, although the treaty explicitly encourages countries to go above and beyond these measures. Despite its lack of mandatory provisions. FCTC ratification and its timing may be good proxy for a country's commitment to tobacco control. Our first objective is to assess the impact of the FCTC on global youth tobacco use. Our second objective is to explore two areas that are amenable to policy change: secondhand smoke and advertising.

Methods:
We used pooled repeated-cross-sectional data from youth surveys conducted between 1999 and 2015 in more than 150 low- and middle-income countries and multilevel analyses to account for the nesting of students in schools and schools in countries. First, we examined the association between three outcome variables (smoking susceptibility, defined as the absence of a firm decision not to smoke, current smoking defined as 30-day smoking prevalence and a five-point scale of smoking uptake) and various indicators of the FCTC implementation. Second, we examined the association between exposure to secondhand smoke and advertising and indicators of the FCTC implementation.

Results:
We found considerable heterogeneity in the association between different measures of youth smoking and indicators of the FCTC implementation. On the whole, we found clearer associations between exposure to secondhand smoke and advertising and indicators of the FCTC implementation.

Conclusions:
A number of studies have examined changes in the implementation of tobacco control measures since the ratification of the FCTC but few studies have examined the effect of the FCTC on tobacco use; fewer still have used pre- and post-FCTC data. More research that use such data is needed.