Growing Evidence for a Causal Role for Smoking in Mental Health

Extract

In this issue, Ibrahim and colleagues¹ report evidence that nicotine dependence (but not smoking per se) is associated with subsequent risk of developing PTSD after trauma and that withdrawal may mediate this association. This study adds to a rapidly growing body of literature, indicating that smoking not only associated with poor mental health, but may be a contributing causal factor. It has long been evident that smoking (and nicotine dependence) is more common among those with mental health problems, but the direction of causality has remained controversial. Does chronic tobacco use lead to neurobiological dysregulation that can contribute to the onset of mental health problems? Or do people with mental health problems smoke to alleviate symptoms? Or is it a combination of both?

Historically, the self-medication argument has been preferred, but this narrative was actively encouraged by the tobacco industry, who sought to market their products to this population.² One inevitable challenge with research of this kind is the reliance on observational data. Even prospective analyses may be inadequate to infer causality with confidence—smoking may be initiated during a prodromal phase before a clinical diagnosis. Nevertheless, smoking is typically initiated in adolescence, whereas the onset of most mental health problems is generally later—in early adulthood and beyond. A meta-analysis of prospective studies concluded that smoking is indeed a causal risk factor for psychosis,³ and a sophisticated analysis taking into account the possible role of a prodromal phase, and comparing across genetically related family members, reached a similar conclusion.⁴