To estimate costs associated with medication non-adherence over a 3-year follow-up period in the treatment of schizophrenia in routine clinical practice in Europe.

SOHO is a 3-year, prospective, observational study of 10972 outpatient participants across 10 European countries. Data were collected at baseline and at 6-month intervals up to 36 months. Medication adherence was assessed at each visit by participating psychiatrists during 4 weeks prior to the visit as: (1) not prescribed medication; (2) always adherent; (3) partially adherent; and (4) never adherent. In this post-hoc analysis, multivariate analyses were performed to compare the costs of resource use (inpatient stay, day care, psychiatrist visits and medication) in patients who were adherent, partially adherent, and non-adherent, using a log-link function. Adherence status was included as a time-varying variable, and other baseline patient characteristics were adjusted for. UK unit costs were applied to resource use.

Out of 5364 patients who were prescribed medication prior to baseline, 5.9% were non-adherent while 77.1% and 17.0% were adherent and partially adherent, respectively, at baseline. The average 6-month cost incurred by non-adherent patients was £2505 while that for adherent and partially adherent patients was £2029 and £2130 respectively. This difference was mainly due to inpatient costs. The inpatient costs incurred by non-adherent patients (£987) were almost double those for adherent patients (£475).

Non-adherence in schizophrenia was likely to incur more inpatient services, which may indicate poorer clinical prognosis. A study limitation is that adherence was assessed by investigators using a single-item measure.