3.1.1 Humans
Males are significantly more likely to use and abuse androgenic anabolic steroids (AAS) compared to females (Kanayama et al., 2010; Kanayama et al., 2018; Wood, 2008). In humans, AAS abuse is often a precursor to the abuse of other drugs, particularly opioids (Kanayama et al., 2003; Skarberg et al., 2009; Kanayama et al., 2009a; Kanayama et al., 2009b). Indeed, several studies have reported a relationship between admission for opioid treatment and a prior history of AAS use (Trenton & Currier, 2005; Kanayama et al., 2009a; Ranjan et al., 2014), leading investigators to conclude that AAS abuse increases the risk of opioid addiction (Kanayama et al., 2018; Kanayama et al., 2003). Opioid use also occurs prior to and concurrently with AAS abuse, suggesting that opioid use also increases susceptibility to AAS abuse (GÄrevik & Rane, 2010; Wines et al., 1999; Ranjan et al., 2014; Skarberg et al., 2009; McBride et al., 1996; Kindlundh et al., 1999). Collectively, such findings suggest that opioid agonists and AAS may mutually enhance the abuse liability of one another, and this may be particularly true in men.