The most consistent predictors of multiple substance dependence diagnoses for both sexes were mental health variables, antisocial behaviours, childhood sexual abuse, younger age at first cannabis use and heroin overdose. The relationship between multiple dependence diagnoses and poorer mental health has been demonstrated previously, as has the risk for overdose and suicide attempts (Darke & Ross, 1997; Darke, et al., 1996; Darke, et al., 2007b). The link between early onset and frequent cannabis use and subsequent other illicit drug use has been demonstrated in other studies and populations (Agrawal, et al., 2006a; Fergusson, Boden, & Horwood, 2008; Lynskey, et al., 2003), and may be partially but not wholly explained by shared genetic and environmental risks (Hall & Lynskey, 2005; Lynskey, et al., 2003; Lynskey, Vink, & Boomsma, 2006). Sexual abuse has also been linked to greater drug related problems and poorer psychosocial functioning amongst women entering opioid replacement treatment (Bartholomew, Courtney, Rowan-Szal, & Simpson, 2005). More generally, childhood sexual abuse has been demonstrated to increase the risk of substance use disorders and early onset drug user over and above the
