A 2020 study published by researchers at UCSF found that JUUL delivers five times more nicotine to the blood, per puff, than a Marlboro cigarette.
Maier, S. (2020). JUUL Delivers Substantially More Nicotine than Previous Generation E-Cigs and Cigarettes. JUUL Delivers Substantially More Nicotine than Previous Generation E-Cigs and Cigarettes | UC San Francisco.
Rao, P., Liu, J., & Springer, M. (2020). JUUL and Combusted Cigarettes Comparably Impair Endothelial Function. Tobacco Regulatory Science, 6(1), 30-37.