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Osong Public Health Res Perspect. 2014 Apr;5(2):92-5. doi: 10.1016/j.phrp.2014.02.003. Epub 2014 Feb 28.

Evaluation of drug abuse relapse event rate over time in frailty model.

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  • 1Department of Biostatistics and Epidemiology, School of Public Health, Hamadan University of Medical Sciences, Hamadan, Iran.
  • 2Modeling of Noncommunicable Disease Research Center, Department of Biostatistics and Epidemiology, School of Public Health, Hamadan University of Medical Sciences, Hamadan, Iran.
  • 3Department of Psychology, Science and Research Branch, Islamic Azad University, Hamadan, Iran.



Drug dependence as a chronic disorder is reversible over time and has a cost burden for individuals, families, and society. An individual who has stopped taking drugs for a long time may start taking drugs again. The variables affecting the reuse of drugs are not well known. Therefore a study of the factors that increase the length of time away from drugs is essential.


This study used data collected by the Bushehr addiction treatment centers (Tolloe and Pasargadae) from 100 men with drug addiction from March 2006 to September 2010. The shared frailty model was used to study the influence of variables on the duration of time away from drug use. The most common method for entering intra-class (personal) correlation is the survival frailty model, which uses parametric survival data for the evaluation of recurrent events. A Weibull distribution for time to event with gamma shared frailty was used.


The mean (standard deviation) age and age at onset of opium use of the sample were 33.85 (8.11) and 20.65 (6.87), respectively. About 30% of the men studied had chronic disease and 36% had a mental illness. The mean (frequency mean) of the amount of opium used were 4.73 (3.8) g and 2.54 (1.14) times per day. The desire to end drug use was 97% and 3% for the men with drug addiction and their families, respectively, at the time when the men stopped using opium. The age at onset of opium use [p = 0.046, hazards ratio (HR) = 1.30], history of chronic disease (p = 0.005, HR = 249.635), and marital status (p = 0.06, HR = 0.027) are important in the reuse of opium.


We found that opium addiction is related to other chronic diseases and to the age at onset of opium use. A prospective study following up individuals with drug addiction who try to stop drug use in addiction treatment centers could help to determine the risk factors of resuming drug use.


drug abuse; frailty model; relapse event

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