Smoking status as a predictor of antidepressant medication use

Cigarette smoking and depression are major public health concerns, but longitudinal research on the association between smoking and antidepressant use is scarce. The purpose of this study was to investigate, whether smoking predicts antidepressant medication during a 10-year follow-up.

A questionnaire was administered to Finnish adult twins in 1990. Antidepressant prescription data during 1995-2004 were obtained from the register of the Finnish Social Insurance Institution and linked to the survey data. Cox Proportional Hazard Models among 10,652 individuals (1075 cases, 9577 controls) assessed the risk for depression in the cohort, whereas within-pair comparisons of smoking twins with their non-smoking co-twins controlled for shared familial influences.

Daily smokers had a significantly elevated likelihood for having antidepressant prescriptions in the follow-up. Based on the analysis among those without baseline depression, heavy daily smokers had a significantly elevated likelihood (HR 1.56, 95% CI 1.17-2.08) for antidepressant prescription when adjusted for all confounders. Similar analysis using pairs discordant for antidepressant medication confirmed that daily smoking twins had a higher likelihood for prescriptions (HR 1.98, 95% CI 1.11-3.54) compared with their non-smoking co-twins. The estimates were for MZ pairs (HR 1.78, 95% CI 0.48-6.55) and DZ pairs (HR 1.92, 95% CI 0.99-3.72), respectively.

Changes in smoking status after baseline cannot be accounted for. Reversed association between depression and smoking cannot be ruled out.

Daily smoking predicts antidepressant medication, even when controlling for essential confounders and familial factors. This study highlights the need of systematically assessing depressive symptoms among smokers.