A study by Kebede (2002) reports that 20% of survey respondents, had started smoking cigarettes and chewing khat at the same time [24]
A list of criteria for an optimal animal model of ADHD was suggested and posits that the model should have impulsiveness be absent initially and gradually develop over time, should sustain attention-deficit behaviors only when stimuli are widely spaced in time, and should not display hyperactivity in a novel environment [7477]
We wrote about those initial studies from 2011 in this article: Cigarettes, E-Cigarettes, and Substance Use in Adolescents The new data from 2019, published in the article Nicotine Gateway Effects on Adolescent Substance Use enhances and expands on the data from 2011
Gallinat J, Meisenzahl E, Jacobsen LK, Kalus P, Bierbrauer J, Kienast T et al