While depression and suicide rates have been on the rise in the United States, so has the use of e - cigarettes, commonly known as vaping. E-cigarettes are considered to be safer than traditional cigarettes, yet there is growing evidence that nicotine and other toxins contained in e-cigarettes may have adverse psychological effects on teenagers. For instance, e-cigarette use has been associated with mental health problems in adolescents such as symptoms of depression and suicidal tendencies. This evidence suggests that vaping could contribute to deteriorating mental health of teenagers. In contrast, the antidepressant and mood modulating properties of nicotine could cause teens with underlying conditions to turn to vaping as a way to self-medicate. Existing studies find evidence of a strong negative correlation between vaping and adolescent mental health; none examine if the relationship is causal. This study exploits exogenous changes in state policies restricting youth access to e- cigarettes and a difference-in-differences methodology to identify changes in e-cigarette use and mental health outcomes of teens. Using data from the 2005-2017 national and state Youth Risk Behavior Surveys, results suggest that MLSA laws reduce vaping but worsen the mental well-being of adolescents. For instance, between 2015-2017, MLSA laws are associated with a 3.0 and 1.8 percentage point increase in depression and suicidal attempts, respectively. These are meaningful increases relative to the overall sample averages of 29% and 8.4%, respectively. The findings are primarily consistent with the self-medication hypothesis. Adverse unintended consequences of the MLSA policy on youth mental health call for the need to address diverse concerns when formulating vaping related regulations for minors.