title: Can differences in the type, nature or amount of polysubstance use explain the increased risk of non-fatal overdose among psychologically distressed people who inject drugs?
abstract: BACKGROUND
  This study investigates whether the type, nature or amount of polysubstance use can explain the increased risk of non-fatal overdose among people who inject drugs with severe psychological distress.
  
  
  METHODS
  Data came from three years (2011-2013) of the Illicit Drug Reporting System (IDRS), an annual sentinel sample of injecting drug users across Australia (n=2673). Structural Equation Modelling (SEM) was used on 14 drug types to construct five latent factors, each representing a type of polysubstance use. Tests of measurement invariance were carried out to determine if polysubstance use profiles differed between those with and without severe psychological distress. Next, we regressed non-fatal overdose on the polysubstance use factors with differences in the relationships tested between groups.
  
  
  RESULTS
  Among those with severe psychological distress a polysubstance use profile characterised by heroin, oxycodone, crystal methamphetamine and cocaine use was associated with greater risk of non-fatal overdose. Among those without severe psychological distress, two polysubstance use profiles, largely characterised by opioid substitution therapies and prescription drugs, were protective against non-fatal overdose.
  
  
  CONCLUSIONS
  The types of polysubstance use profiles did not differ between people who inject drugs with and without severe psychological distress. However, the nature of use of one particular polysubstance profile placed the former group at a strongly increased risk of non-fatal overdose, while the nature of polysubstance use involving opioid substitution therapies was protective only among the latter group. The findings identify polysubstance use profiles of importance to drug-related harms among individuals with psychological problems.
authors.affiliation: The University of Queensland, Australia. Electronic address: kim.betts@uqconnect.edu.au.
authors.forename: Kim S
authors.initials: KS
authors.lastname: Betts
authors.affiliation: QADREC, Level 3, School of Population Health Building, University of Queensland, Brisbane, Australia. Electronic address: f.mcilwraith@sph.uq.edu.au.
authors.forename: Fairlie
authors.initials: F
authors.lastname: McIlwraith
authors.affiliation: MacFarlane Burnet Institute for Medical and Public Health Research, Melbourne, Australia. Electronic address: pauld@burnet.edu.au.
authors.forename: Paul
authors.initials: P
authors.lastname: Dietze
authors.affiliation: National Drug and Alcohol Centre, University of New South Wales, NSW 2052, Australia. Electronic address: e.whittaker@unsw.edu.au.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Whittaker
authors.affiliation: National Drug and Alcohol Centre, University of New South Wales, NSW 2052, Australia. Electronic address: l.burns@unsw.edu.au.
authors.forename: Lucy
authors.initials: L
authors.lastname: Burns
authors.affiliation: MacFarlane Burnet Institute for Medical and Public Health Research, Melbourne, Australia. Electronic address: shelley@burnet.edu.au.
authors.forename: Shelley
authors.initials: S
authors.lastname: Cogger
authors.affiliation: School of Public Health and Centre for Youth Substance Abuse Research, University of Queensland, Brisbane, Australia. Electronic address: r.alati@sph.uq.edu.au.
authors.forename: Rosa
authors.initials: R
authors.lastname: Alati
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001315:Australia / Q000453:epidemiology; D062787:Drug Overdose / Q000453:epidemiology* / Q000209:etiology / Q000523:psychology*; D055030:Drug Users / Q000523:psychology*; D005260:Female; D006801:Humans; D013287:Illicit Drugs / Q000506:poisoning*; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D012309:Risk-Taking; D013315:Stress, Psychological / Q000150:complications / Q000523:psychology*; D015819:Substance Abuse, Intravenous / Q000150:complications / Q000453:epidemiology* / Q000523:psychology*; D055815:Young Adult
chemical_list: D013287:Illicit Drugs
keywords: Non-fatal overdose; Polysubstance use; Psychological distress; Structural equation modelling