Characterizing longitudinal health state transitions among heroin, cocaine, and methamphetamine users.
OBJECTIVE
Characterize longitudinal patterns of drug use careers and identify determinants of drug use frequency across cohorts of primary heroin, methamphetamine (MA) and cocaine users.


METHODS
Pooled analysis of prospective cohort studies.


METHODS
Illicit drug users recruited from community, criminal justice and drug treatment settings in California, USA.


METHODS
We used longitudinal data on from five observational cohort studies featuring primary users of heroin (N=629), cocaine (N=694) and methamphetamine (N=474). The mean duration of follow-up was 20.9 years.


METHODS
Monthly longitudinal data was arranged according to five health states (incarceration, drug treatment, abstinence, non-daily and daily use). We fitted proportional hazards (PH) frailty models to determine independent differences in successive episode durations. We then executed multi-state Markov (MSM) models to estimate probabilities of transitioning between health states, and the determinants of these transitions.


RESULTS
Across primary drug use types, PH frailty models demonstrated durations of daily use diminished in successive episodes over time. MSM models revealed primary stimulant users had more erratic longitudinal patterns of drug use, transitioning more rapidly between periods of treatment, abstinence, non-daily and daily use. MA users exhibited relatively longer durations of high-frequency use. Criminal engagement had a destabilizing effect on health state durations across drug types. Longer incarceration histories were associated with delayed transitions toward cessation.


CONCLUSIONS
PH frailty and MSM modeling techniques provided complementary information on longitudinal patterns of drug abuse. This information can inform clinical practice and policy, and otherwise be used in health economic simulation models, designed to inform resource allocation decisions.
BC Centre for Excellence in HIV/AIDS, Vancouver, British Columbia V6Z 2C7, Canada; Faculty of Health Sciences, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada; UCLA Integrated Substance Abuse Programs, Los Angeles, CA 90025, USA.
B
B
Nosyk
UCLA Integrated Substance Abuse Programs, Los Angeles, CA 90025, USA.
L
L
Li
UCLA Integrated Substance Abuse Programs, Los Angeles, CA 90025, USA.
E
E
Evans
UCLA Integrated Substance Abuse Programs, Los Angeles, CA 90025, USA.
D
D
Huang
BC Centre for Excellence in HIV/AIDS, Vancouver, British Columbia V6Z 2C7, Canada.
J
J
Min
BC Centre for Excellence in HIV/AIDS, Vancouver, British Columbia V6Z 2C7, Canada; Division of AIDS, Faculty of Medicine, University of British Columbia, Vancouver, British Columbia V5Z 1M9, Canada.
T
T
Kerr
UCLA Integrated Substance Abuse Programs, Los Angeles, CA 90025, USA.
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ML
Brecht
UCLA Integrated Substance Abuse Programs, Los Angeles, CA 90025, USA. Electronic address: yhser@ucla.edu.
Y I
YI
Hser
D000328:Adult; D019969:Amphetamine-Related Disorders / Q000453:epidemiology / Q000503:physiopathology* / Q000534:rehabilitation; D002140:California / Q000453:epidemiology; D000697:Central Nervous System Stimulants; D019970:Cocaine-Related Disorders / Q000453:epidemiology / Q000503:physiopathology* / Q000534:rehabilitation; D015331:Cohort Studies; D003415:Crime / Q000706:statistics & numerical data; D005260:Female; D005500:Follow-Up Studies; D006304:Health Status; D006556:Heroin Dependence / Q000453:epidemiology / Q000503:physiopathology* / Q000534:rehabilitation; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008694:Methamphetamine; D008875:Middle Aged; D012959:Socioeconomic Factors
D000697:Central Nervous System Stimulants; D008694:Methamphetamine
Drug use careers; Health state transitions; Longitudinal; Multi-state Markov; Proportional hazards frailty