Nicotine Vapes - Look at the effective dosage of JUULs capsules for example [0]. This combined with the ease of use, the removal of the (unpleasant) smoke, increased social acceptance (often indoors too) and a huge advertising campaign deliberately targeting teens [1] created a lot of new smokers/nicotine addicts (and converted some) that smoke more often and at much higher dosages.
[0] https://www.ucsf.edu/news/2020/01/416371/juul-delivers-subst...
The research found that blood nicotine concentrations in the JUUL group (136.4 ng/ml) was eight times higher than e-cigs group (17.1 ng/ml) and 5.2 times higher than cigarettes (26.1 ng/ml).
[1]
https://truthinitiative.org/research-resources/emerging-toba...