Introduction:
France is the European country where the prohibition of cannabis is the strongest in EU. France is also a country where cannabis use is the highest. Since 2012 the emergence of the electronic cigarette (ecig) has profoundly changed the consumption of tobacco among Parisian teenagers. We wanted to study the cannabis used in ecig users, compared to tobacco users.

Methods:
We analyzed the 2012-2018 cross-sectional surveys of Paris sans tabac conducted on 2% of classes randomly designed from the list of school authorities of Paris.

Results:
The rate of the 20 829 students who report cannabis experimentation is 11.6% among the 16592 no tobacco or vape users the last 30 days, 38.4% among the 625 only ecig-users, 68.0% among the 2596 only tobacco users, 78.8% among the 1 014 dual (ecig and tobacco) users.

Conclusions:
There is a strong negative relationship between regular consumption of ecig and low rate of use of cannabis. No causal link can be established from our data. The most likely hypothesis is a preferential experimentation of ecig by young students who don’t want experiment bad products (tobacco, cannabis,..). Tobacco users have more temperament to use all products including cannabis and alcohol (data non-reported). Overall, while the increase of cannabis use has been constant for 10 years, since 2012, the emergence of ecig was associated with a decrease of cannabis use among students. If no causal link could be established, present data’s are inconsistent with a gateway effect of ecig use on cannabis experimentation.