title: Factors affecting repeated cessations of injecting drug use and relapses during the entire injecting career among the Edinburgh Addiction Cohort.
abstract: OBJECTIVE
  Injecting drug use is a chronic condition, with people who inject drugs (PWID) typically experiencing repeated cessations and relapses during their injection careers. We characterize patterns of ceasing and relapsing and the impact of opiate substitution treatment (OST) during the entire injecting careers of PWID in the Edinburgh Addiction Cohort (EAC).
  
  
  METHODS
  During 2005-2007, 432 surviving participants of the EAC were interviewed about their injecting histories. Adjusted associations between covariates and hazards of cessation and relapse were estimated using random-effects models.
  
  
  RESULTS
  OST was strongly associated with a higher hazard of cessation (HR = 1 .71, P < 0.001), but there was no significant evidence of association with hazard of relapse (HR = 0.81, P = 0.14). Women and older PWID were less likely to relapse (HR = 0.73, P = 0.02 and HR = 0.55, P < 0.001, respectively). Hazards of both cessation and relapse decreased monotonically with time since last relapse/cessation (both P < 0.001). An individual's hazard of cessation increased with his/her number of previous cessations (HR = 3.58 for 10+ previous cessations, P < 0.001), but there was no evidence that an individual's hazard of relapse changed with number of previous relapses (P = 0.37). There was heterogeneity in the individual hazards of both cessation and relapse.
  
  
  CONCLUSIONS
  OST was associated with reduced time to cessation, and there was some suggestion of increased time to relapse too. The likelihood of prolonged cessation is greater for women, increases with age, and decreases with time since last relapse.
authors: MRC Biostatistics Unit, Cambridge Institute of Public Health, Forvie Site, Robinson Way, Cambridge Biomedical Campus, Cambridge CB2 0SR, UK.
authors: Yang
authors: Y
authors: Xia
authors: MRC Biostatistics Unit, Cambridge Institute of Public Health, Forvie Site, Robinson Way, Cambridge Biomedical Campus, Cambridge CB2 0SR, UK.
authors: Shaun
authors: S
authors: Seaman
authors: School of Social and Community Medicine, University of Bristol, Canynge Hall, 39 Whatley Road, Bristol BS8 2PS, UK.
authors: Matthew
authors: M
authors: Hickman
authors: School of Social and Community Medicine, University of Bristol, Canynge Hall, 39 Whatley Road, Bristol BS8 2PS, UK.
authors: John
authors: J
authors: Macleod
authors: Centre for Population Health Sciences, The University of Edinburgh, Medical Quad, Teviot Place, Edinburgh EH8 9AG, UK; Muirhouse Medical Group, 1 Muirhouse Avenue, Muirhouse, Edinburgh EH4 4PL, UK.
authors: Roy
authors: R
authors: Robertson
authors: Muirhouse Medical Group, 1 Muirhouse Avenue, Muirhouse, Edinburgh EH4 4PL, UK.
authors: Lorraine
authors: L
authors: Copeland
authors: Muirhouse Medical Group, 1 Muirhouse Avenue, Muirhouse, Edinburgh EH4 4PL, UK.
authors: Jim
authors: J
authors: McKenzie
authors: MRC Biostatistics Unit, Cambridge Institute of Public Health, Forvie Site, Robinson Way, Cambridge Biomedical Campus, Cambridge CB2 0SR, UK; Public Health England, Statistics, Modelling and Economics Department, Centre for Infectious Disease Surveillance and Control, 61 Colindale Avenue, London NW9 5EQ, UK.
authors: Daniela
authors: D
authors: De Angelis
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D016739:Behavior, Addictive / Q000209:etiology*; D002648:Child; D002908:Chronic Disease; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D058850:Opiate Substitution Treatment / Q000706:statistics & numerical data*; D012008:Recurrence; D012606:Scotland; D015819:Substance Abuse, Intravenous / Q000150:complications*; D013997:Time Factors; D055815:Young Adult
keywords: Cessation; Heroin addiction; Opiate substitution treatment; Random effects model; Recurrent events; Relapse