, 2013). Numerous studies have shown that underlying early drug use is a general, highly heritable predisposition to externalizing behaviors (Agrawal and Lynskey, 2006). At the same time, it has been suggested that although illicit drug use and dependence is associated with a

range of early life circumstances that put individuals at greater risk, the use of cannabis in late adolescence emerge as the strongest risk factor for later illicit drug use (Fergusson et al., 2008). This is supported by twin studies, reporting early-onset cannabis see more users to be at two to four times greater risk of use of drugs such as cocaine, hallucinogens, sedatives and opioids and twice as likely as their co-twins to meet criteria for dependence on hard drugs and alcohol (Agrawal and Lynskey, 2014 and Lynskey et al., 2003). In our study, 80% of the extensive cannabis users reported

having also used other drugs, unknown to what extent. Existing research indicates that individuals with poly-substance use experience greater social consequences and higher rates of dependence, when compared to individuals who use only one drug (Midanik et al., 2007, Pacek et al., 2013 and Stenbacka, 2003). Nevertheless, research on poly-substance use in relation to health and psychosocial functioning is scarce (Martin, 2008). Findings suggest psychiatric severity increases linearly because with increased poly-substance Vandetanib mw use (Fischer et al., 2010) and poly-drug users to be at increased risk of unemployment (Carter et al., 2013 and Quek et al., 2013). Our study did, however, focus on disability pension (i.e., a permanent exclusion from the labor market with a medical diagnosis). Also, important to highlight is the fact that when we controlled for use of other drugs the association between adolescent cannabis

use and DP still remained. We are not able to fully explain the mechanisms which underlie the observed associations between adolescent cannabis use and later DP. For example, there is reason to believe that the associations found in our study develop over a long period of time and are intertwined with problems in the both the labor market, in the social security system, and with the individual. For one thing, we know from previous studies that drug use and dependence are associated with many psychiatric disorders (Goldstein et al., 2012), which in turn represents a large proportion of the disability pensions in Sweden. When we adjusted for mental functions (e.g., psychiatric diagnosis, cognitive ability, emotional stability and social maturity) by the age of 18, the associations weakened considerably. We have, however, no knowledge of the later diagnoses leading to DP in our population.