title: Adherence to antipsychotic medication among homeless adults in Vancouver, Canada: a 15-year retrospective cohort study.
abstract: The purpose of this study was to investigate the level of adherence to antipsychotic prescription medication in a well-defined homeless cohort over a 15-year period. We hypothesized that adherence would be well below the recommended threshold for clinical effectiveness (80 %), and that it would be strongly associated with modifiable risk factors in the social environment in which homeless people live.
  
  
  
  Linked baseline data (including comprehensive population-level administrative prescription records) were examined in a subpopulation of participants from two pragmatic-randomized trials that investigated Housing First for homeless and mentally ill adults. Adherence to antipsychotic medication was operationalized using the medication possession ratio. Multivariable logistic regression was used to estimate effect sizes between socio-demographic, homelessness-related and illness factors, and medication possession ratio.
  
  
  
  Among the 290 participants who met inclusion criteria for the current analysis, adherence to antipsychotic prescription was significantly associated with: history of psychiatric hospitalization; receipt of primary medical services; long-acting injectable antipsychotic formulations; and duration of homelessness. Mean medication possession ratio in the pre-randomization period was 0.41. Socio-demographic characteristics previously correlated with antipsychotic non-adherence were not significantly related to medication possession ratio.
  
  
  
  This is the first study to quantify the very low level of adherence to antipsychotic medication among homeless people over an extended observation period of 15 years. Each of the four factors found to be significantly associated with adherence presents opportunities for intervention. Strategies to end homelessness for this population may represent the greatest opportunity to improve adherence to antipsychotic medication.
authors.affiliation: Faculty of Health Sciences, Simon Fraser University, 8888 University Drive, Burnaby, BC, V5A 1S6, Canada. sra20@sfu.ca.
authors.forename: Stefanie N
authors.initials: SN
authors.lastname: Rezansoff
authors.affiliation: Faculty of Health Sciences, Simon Fraser University, 8888 University Drive, Burnaby, BC, V5A 1S6, Canada.
authors.forename: A
authors.initials: A
authors.lastname: Moniruzzaman
authors.affiliation: Department of Psychiatry, University of Oxford, Warneford Hospital, Oxford, 0X3 7JX, UK.
authors.forename: S
authors.initials: S
authors.lastname: Fazel
authors.affiliation: Department of Psychiatry, Faculty of Medicine, University of British Columbia, 2255 Wesbrook Mall, Vancouver, BC, V6T 2A1, Canada.
authors.forename: R
authors.initials: R
authors.lastname: Procyshyn
authors.affiliation: Faculty of Health Sciences, Simon Fraser University, 8888 University Drive, Burnaby, BC, V5A 1S6, Canada.
authors.forename: J M
authors.initials: JM
authors.lastname: Somers
mesh_terms: D000328:Adult; D014150:Antipsychotic Agents / Q000627:therapeutic use*; D001955:British Columbia / Q000453:epidemiology; D005260:Female; D006703:Ill-Housed Persons / Q000706:statistics & numerical data*; D006801:Humans; D008297:Male; D001523:Mental Disorders / Q000188:drug therapy* / Q000453:epidemiology; D028642:Persons with Psychiatric Disorders / Q000706:statistics & numerical data*; D008875:Middle Aged; D012189:Retrospective Studies; D016903:Drug Monitoring
chemical_list: D014150:Antipsychotic Agents
keywords: Adherence; Antipsychotic; Homelessness; Medication possession ratio; Serious mental illness