Co-occurrence between mental distress and poly-drug use: A ten year prospective study of patients from substance abuse treatment Jasmina Burdzovic Andreas ⁎ ,1 , Grethe Lauritzen ⁎ ,1 , Trond Nordfjærn Norwegian Institute for Alcohol and Drug Research (SIRUS), Øvre Slottsgate 2B, 0157 Oslo, Norway HIGHLIGHTS • Trajectories of mental health and poly-drug use were examined over 10 years. • Elevated poly-drug use was prospectively associated with elevated mental distress. • Mental distress systematically increased with a greater number of used drugs. • Abstinence from the studied drugs was related to reduced mental distress. • Assessment and treatment need to be better tailored to poly-substance users. abstract article info Available online 8 May 2015 Keywords: Prospective clinical study Longitudinal trajectories Co-occurrence between mental distress and poly-drug use Introduction: Longitudinal research investigating psychiatric trajectories among patients with poly-drug use pat- terns remains relatively scant, even though this specific population is at elevated risk for multiple negative out- comes. The present study examined temporal associations between poly-drug use (i.e. heroin, cannabis, tranquilizers, and amphetamines) and mental distress over a 10-year period. Methods: A clinical cohort of 481 patients was recruited from substance use treatment facilities in Norway, and prospectively interviewed 1, 2, 7 and 10 years after the initial data collection at treatment admission. At each as- sessment participants completed a questionnaire addressing their substance use and mental distress. Longitudi- nal growth models were used to examine whether, and if so, how, levels of drug use were associated with the level and rate of change in mental distress over time. Results: Results from the longitudinal growth models showed a co-occurrence between active poly-drug use and mental distress, such that there was a dose–response effect where mental distress increased both in magnitude and over time with the number of drugs used. Reduction in mental distress during the 10-year study period was evident only in the no-drug use condition. Use of multiple drugs and mental distress appear strongly co-related over time. Conclusions: Pre-treatment assessment should carefully identify individuals manifesting poly-drug use and mental disorders. Treatment and follow-up services should be tailored to their specific needs. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Findings from multiple studies testify to general co-occurrence be- tween substance use problems and mental health disorders (including mood, anxiety, depression, and suicidality), both among adult (Compton, Thomas, Stinson, & Grant, 2007; Conway, Compton, Stinson, & Grant, 2006; Grant et al., 2004; Kessler et al., 1997; Merikangas et al., 1998) and youth populations (Chi, Sterling, & Weisner, 2006; Green, Zebrak, Robertson, Fothergill, & Ensminger, 2012; Kokkevi et al., 2012; McGee, Williams, Poulton, & Moffitt, 2000; O'Neil, Conner, & Kendall, 2011; Roberts, Roberts, & Xing, 2007). A recent review of the (English language) literature on co-occurrence between mental health and substance abuse problems concluded on the strong association between the two, both in epidemiological and clinical studies (Morisano, Babor, & Robaina, 2014). Understanding the general relationship between substance use and mental health is thus of great importance as these problems may adversely influence one another and shape the prevention/intervention strategies as well as the treatment completion and recovery (Cacciola, Alterman, Rutherford, McKay, & Mulvaney, 2001; Chi et al., 2006; Kavanagh & Connolly, 2009; Kessler et al., 1996; Landheim, Bakken, & Vaglum, 2006; McGovern, Xie, Segal, Siembab, & Drake, 2006). It ap- pears that mental health problems are particularly pronounced among Addictive Behaviors 48 (2015) 71–78 ⁎ Corresponding authors. Tel.: +47 40 60 36 38, fax: +47 22 34 04 01. E-mail addresses: jba@sirus.no (J. Burdzovic Andreas), gl@sirus.no (G. Lauritzen). 1 Corresponding authors contributed equally as First Authors and the listing order was determined alphabetically. http://dx.doi.org/10.1016/j.addbeh.2015.05.001 0306-4603/© 2015 Elsevier Ltd. All rights reserved. Contents lists available at ScienceDirect Addictive Behaviors