Subthreshold psychotic and bipolar experiences are common in major depressive disorder (MDD). However, it is unknown if effectiveness of psychotherapy is altered in depressed patients who display such features compared with those without. The current paper aimed to investigate the impact of the co-presence of subclinical psychotic experiences and subclinical bipolar symptoms on the effectiveness of psychological treatment, alone or in combination with pharmacotherapy.

In a naturalistic study, patients with MDD (n = 116) received psychological treatment (cognitive behavioural therapy or interpersonal psychotherapy) alone or in combination with pharmacotherapy. Depression and functioning were assessed six times over 2 years. Lifetime psychotic experiences and bipolar symptoms were assessed at the second time point.

Subclinical psychotic experiences predicted more depression over time (β = 0.20, p < 0.002), non-remission [odds ratio (OR) 7.51, p < 0.016] and relapse (OR 3.85, p < 0.034). Subthreshold bipolar symptoms predicted relapse (OR 1.16, p < 0.037).

In general, subclinical psychotic experiences have a negative impact on the course and outcome of psychotherapy in MDD. Effects of subclinical bipolar experiences were less prominent.