To assess frequency and baseline factors associated with adherence with antipsychotic medication during long-term treatment in outpatients with schizophrenia.

SOHO is a 3-year, prospective, observational study that included 10 972 patients changing or starting a new antipsychotic medication Treatment adherence during 4 weeks prior to the visit was assessed at each visit by participating psychiatrists as:

• • the patient has not been prescribed medication;

• • the patient almost always adheres;

• • the patient adheres half of the time; and

• • the patient never adheres to antipsychotic medication.

6731 patients with at most one missing visit were analysed. Data from the missing visit were imputed from the previous visit; 71.2% were considered to be adherent and 28.8% non-adherent over the 3-year follow-up period. the strongest predictor of medication adherence during follow-up was adherence at baseline (OR = 4.01, 95% CI: 3.46-4.64). other baseline predictors of adherence included not using antipsychotics in the previous 4 weeks, receiving treatment for first time, being socially active, and a higher body mass index. Baseline predictors of non-adherence were alcohol dependence, substance abuse, hospitalisation in previous 6 months, living independently housing and having hostile behaviours.

Alcohol dependence, substance abuse and living independently were associated with non-adherence. Previous adherence, being socially active and receiving medication for the first time was associated with better adherence. Limitation: medication adherence was assessed by the psychiatrist through a single item question.