At baseline, suicidal thoughts were very rare in this young population and there was a strong overlap with early onset-depression. To explore further, as an incidence analysis, we examined the effect of early onset tobacco use among females, who did not report any suicidal thoughts at baseline. Also here, those with early tobacco exposure had higher liability to incident suicidal ideation compared to those who had not initiated tobacco use by age 22. Thus, in this analysis we were able to control for pre-existing suicidal thoughts occurring before tobacco use assessment at age 14 baseline. However, we acknowledge as a limitation of this prospective study, that we did not have data for pre-existing intentional self-injury at baseline. Thus, for this SRB, we cannot rule out the possibility that lifetime self-injury reported as young adult had actually appeared before the assessment of baseline tobacco use.
