Delay discounting correlates with depression but does not predict relapse after antidepressant discontinuation

Background: Approximately one third of people with major depressive disorder experience a relapse within six months of discontinuing antidepressant medication (ADM), however, reliable predictors of relapse following ADM discontinuation are currently lacking. A putative behavioural predictor is delay discounting, which measures a person’s impatience to receive reward. Delay discounting is linked to both depression and reduced serotonergic function, rendering it a plausible candidate predictor. Methods: In a multi-site study we measured delay discounting in participants with remitted depression (N=97), before and within six months after discontinuation of ADM, and in matched controls without a lifetime history of depression (N=54). Using predictive models, we tested whether either baseline discounting, or an early change in discounting following ADM discontinuation, predicted depressive relapse over a six month follow up period. We also tested differences between remitted depression and control groups in delay discounting at baseline, and associations between discounting and depressive symptoms. Results: The remitted depression group, compared to the control group, showed significantly higher (p<0.05; Cohen’s d=0.34) discounting at baseline. In addition, baseline discounting was positively correlated with depression rating scores (Spearman ρ= 0.24). However, delay discounting did not increase following ADM discontinuation. Neither baseline discounting nor a change in discounting following ADM discontinuation predicted subsequent depressive relapse. Conclusions: Delay discounting remains elevated in remitted, medicated depression. However, delay discounting neither increases following ADM discontinuation, nor does it prospectively predict depressive relapse. Impulsivity in depression has little relationship with illness trajectory following ADM discontinuation.