Carolien Zeetsen

19 CHAPTER General introduction 1 Cannabis Cannabis has been used both for recreational and medical purposes, and the potential cognitive consequences have been summarized recently (Le Foll & Tyndale, 2015). Currently, cannabis is considered the most frequently used illicit drug worldwide (Pope Jr et al., 2001). The acute consequences of intoxication primarily act upon the short–termmemory, executive functioning and attention (Lundqvist, 2005). The long–term effects have been topic of much debate (Pope Jr et al., 2001). The effects would be noticeable after 17 hours (Solowij et al., 2002), seven days (Pope Jr et al., 2001) and even after 21 days of abstinence in the executive functioning domain (Crean et al., 2011), but the long term post–acute effects (more than 28 days) are assumed to be largely reversible (Pope Jr et al., 2001; van Holst et al., 2011). Indeed, a meta–analysis by Grant et al. (2003) showed that the effect sizes of the non–acute effects are zero for the majority of the cognitive domains. Only on general intelligence it was found that after 20 years of abstinence, users performed worse than non–users. However, after careful examination of the results, it appeared that this was only on one subtest of this domain, and a trend was present of users performing actually better than non–users on several other subtests. It was therefore concluded that long–term cognitive consequences of cannabis use are negligible (Lyons et al., 2004). Likewise, Schulte et al. (2014) mentioned that it is the only drug of which full recovery is possible, and Fernández–Serrano et al. (2011) concluded in their review that long–term effects are absent. Stimulants Concerning stimulant abuse, cocaine and methamphetamine have been of particular interest as they are widely used. For cocaine use, the cognitive deficits are considered to be relatively mild (Goldstein et al., 2004). Interestingly, the literature suggests that psychostimulants produce both cognitive enhancement and impairment. It is proposed that dose is the critical determinant herein, following an inverted U–shape when related to performance (Wood et al., 2014). Alternatively, it is argued that the effects of cocaine during acute intoxication and during abstinence seem to oppose each other, being generally advantageous and detrimental for cognitive functioning, respectively (Spronk et al., 2013). The acute effects of both cocaine and methamphetamine are highly similar, with cocaine use being associated with improved response inhibition, speed and psychomotor performance (Spronk et al., 2013), and methamphetamine use being associated with increased processing speed and alertness, although selective attention diminishes (Scott et al., 2007). In the acute stages of cocaine abstinence, decision making abilities may be negatively affected (Tucker et al., 2004). Cunha et al. (2004) have reported evidence for impairments in attention, memory, learning ability, and executive functions in chronic cocaine abusers after two weeks of abstinence. Regarding the effects during prolonged abstinence, both cocaine and methamphetamine abusers show decrements in executive functioning, inhibition, (verbal) memory and psychomotor functions (Scott et al., 2007; van Holst et al., 2011; Spronk et al., 2013). Jovanovski et al. (2005) conducted a