The effect of financial incentives on adherence to antipsychotic depot medication: does it change over time?

Objective: A recent cluster-randomized controlled trial found that offering financial incentives improves adherence to long-acting injectable antipsychotics (LAIs). The present study investigates whether the impact of incentives diminishes over time and whether the improvement in adherence is linked to the amount of incentives offered.

Method: Seventy-three teams with 141 patients with psychotic disorders (using ICD-10) were randomized to the intervention or control group. Over 1 year, patients in the intervention group received £15 (US $23) for each LAI, while control patients received treatment as usual. Adherence levels, ie, the percentage of prescribed LAIs that were received, were calculated for quarterly intervals. The amount of incentives offered was calculated from the treatment cycle at baseline. Multilevel models were used to examine the time course of the effect of incentives and the effect of the amount of incentives offered on adherence.

Results: Adherence increased in both the intervention and the control group over time by an average of 4.2% per quarterly interval (95% CI, 2.8%-5.6%; P < .001). Despite this general increase, adherence in the intervention group remained improved compared to the control group by between 11% and 14% per quarterly interval. There was no interaction effect between time and treatment group. Further, a higher total amount of incentives was associated with poorer adherence (βbootstrapped = -0.11; 95% CIbootstrapped, -0.20 to -0.01; P = .023).

Conclusions: A substantial effect of financial incentives on adherence to LAIs occurs within the first 3 months of the intervention and is sustained over 1 year. A higher total amount of incentives does not increase the effect.

Trial Registration: ISRCTN.com identifier: ISRCTN77769281 and UKCRN.org identifier: 7033.