Juul ramped up nicotine levels, and competitors followed, study says - CNN

Leading e-cigarette company Juul Labs spurred a "widespread rush" of companies seeking to boost their own nicotine concentrations in order to mirror Juul's success, according to a paper published Thursday in the BMJ journal Tobacco Control.....
https://www.cnn.com/2019/02/07/health/juul-nicotine-arms-race-study/index.html