Background: Offering a modest financial incentive to people with psychosis can promote adherence to depot antipsychotic medication, but the cost-effectiveness of this approach has not been examined.
Methods: Economic evaluation within a pragmatic cluster-randomised controlled trial. 141 patients under the care of 73 teams (clusters) were randomised to intervention or control; 138 patients with diagnoses of schizophrenia, schizo-affective disorder or bipolar disorder participated. Intervention participants received £15 per depot injection over 12 months, additional to usual acute, mental and community primary health services. The control group received usual health services. Main outcome measures: incremental cost per 20% increase in adherence to depot antipsychotic medication; incremental cost of 'good' adherence (defined as taking at least 95% of the prescribed number of depot medications over the intervention period).
Findings: Economic and outcome data for baseline and 12-month follow-up were available for 117 participants. The adjusted difference in adherence between groups was 12.2% (73.4% control vs. 85.6% intervention); the adjusted costs difference was £598 (95% CI -£4,533, £5,730). The extra cost per patient to increase adherence to depot medications by 20% was £982 (95% CI -£8,020, £14,000). The extra cost per patient of achieving 'good' adherence was £2,950 (CI -£19,400, £27,800). Probability of cost-effectiveness exceeded 97.5% at willingness-to-pay values of £14,000 for a 20% increase in adherence and £27,800 for good adherence.
Interpretation: Offering a modest financial incentive to people with psychosis is cost-effective in promoting adherence to depot antipsychotic medication. Direct healthcare costs (including costs of the financial incentive) are unlikely to be increased by this intervention.
Trial registration: ISRCTN.com 77769281.