Tobacco use does not influence the response to non-pharmacologic depression treatment: A secondary analysis of the Regassa randomized controlled trial

Behavioural interventions show promising results among patients with mild- to moderate depression. However, whether tobacco use moderates the effects of these interventions is not known. In the present study, we examined whether patients suffering from mild-to-moderate depression differed in their response to prescribed physical exercise or internet-based cognitive behavioural therapy (ICBT) according to their current tobacco use. We conducted a secondary analysis of data from 740 participants in a multicentre randomised controlled trial comparing physical exercise, internet-based cognitive behavioural therapy and treatment as usual (Regassa study). Information on current daily tobacco use was self-reported at baseline. Linear and logistic regression were used to examine the treatments' effect (reduction in depression score) in the subgroups of tobacco users (n=154) and non-users (n=586). We found that baseline tobacco use did not significantly moderate the association between treatment type and post-treatment depression severity. Both interventions (exercise and ICBT) resulted in a reduction of depression scores that was similar among non-users and users of tobacco, albeit formally statistically significant only among non-users. Physical exercise on prescription and ICBT can be used in the clinical management of depressed patients, with similar prognostic advantage among tobacco users and non-users.