BackgroundWith the development of evidence-based interventions for treatment of priority mental health conditions in humanitarian settings, it is important to establish the cost-effectiveness of such interventions to enable their scale-up.AimsTo evaluate the cost-effectiveness of the Problem Management Plus (PM+) intervention compared with enhanced usual care (EUC) for common mental disorders in primary healthcare in Peshawar, Pakistan. Trial registration ACTRN12614001235695 (anzctr.org.au).MethodWe randomly allocated 346 participants to either PM+ (n = 172) or EUC (n = 174). Effectiveness was measured using the Hospital Anxiety and Depression Scale (HADS) at 3 months post-intervention. Cost-effectiveness analysis was performed as incremental costs (measured in Pakistani rupees, PKR) per unit change in anxiety, depression and functioning scores.ResultsThe total cost of delivering PM+ per participant was estimated at PKR 16 967 (US$163.14) using an international trainer and supervisor, and PKR 3645 (US$35.04) employing a local trainer. The mean cost per unit score improvement in anxiety and depression symptoms on the HADS was PKR 2957 (95% CI 2262–4029) (US$28) with an international trainer/supervisor and PKR 588 (95% CI 434–820) (US$6) with a local trainer/supervisor. The mean incremental cost-effectiveness ratio (ICER) to successfully treat a case of depression (PHQ-9 ≥ 10) using an international supervisor was PKR 53 770 (95% CI 39 394–77 399) (US$517), compared with PKR 10 705 (95% CI 7731–15 627) (US$102.93) using a local supervisor.ConclusionsThe PM+ intervention was more effective but also more costly than EUC in reducing symptoms of anxiety, depression and improving functioning in adults impaired by psychological distress in a post-conflict setting of Pakistan.