Effectiveness of parenteral antipsychotics (PAP) to prevent relapses in persons with severe mental disorders (SMD) is limited by adherence. However, data about potential risk factors for non- or partial compliance with PAP are relatively scarce and inconsistent.

to determine variables associated with partial compliance in a naturalistic one-site study.

The sample comprised all outpatients with SMD treated with PAP over a 12–month period at one mental health unit in Spain. Different sets of broadly– and narrowly–defined criteria for adherence were calculated from mental health nurse´s registry data. Retrospective chart review yielded sociodemographic (age, gender, educational level, civil and vocational status) and clinical (ICD–10 diagnosis, age of onset, illness duration, number of admissions, past/current substance abuse disorders, and community treatment order) variables.

Forty-nine patients were identified; most were single (83%), received a government pension (73%) and lived with their family (67%). When the strictest criteria for adherence were used, illness duration was positively associated with a > 4 day-delay in PAP injection (r=0.36; p=0.01). Furthermore, patients under community treatment orders (χ2=7.5; p=0.006) and those with past substance abuse (χ2=8.9; p=0.003) showed higher rates of non–compliance. This latter variable was the only predictor of non–compliance (exp.β=0.15; IC 95%=0.04– 0.6; p=0.007) and correctly classified 80% of the sample (χ2=8.3; R2=0.23; p=0.004).

Confirming previous results, substance abuse may lead to a poorer compliance with parenteral antipsychotics. Conversely, demographic variables would play a less relevant role in adherence to PAP.