Carolien Zeetsen

20 meta–analysis and concluded that in cocaine use disorder the largest effect size was found for attention and moderate effect sizes for memory. Longitudinal research suggests that at least partial recovery is possible after abstinence: Zhong et al. (2016) showed improvements in most cognitive domains inmethamphetamine users after six months of abstinence. After one year of complete abstinence, cognitive functioning was found to be undistinguishable fromnon–using controls, both for cocaine users (Vonmoos et al., 2014) and methamphetamine users (Iudicello et al., 2010). Remarkably, a short period of abstinence of cocaine use is associated with less neuropsychological deficits than a longer period. A possible explanation is that recent cocaine use may mask possible deficits (Woicik et al., 2009; Schulte et al., 2014). Opioids Regarding opiate use, which includes substances like opium, heroin, codeine and morphine, relatively few studies have assessed the acute effects of substance intake. In their review, Gruber et al. (2007) describe evidence for impairments in the memory domain. More recently, Kroll et al. (2018) found that opioid users were significantly impaired as compared to non– users in the domains attention, declarative memory and global cognitive empathy, for which a negative dose–dependent correlation was found. The effects during abstinence are deficits in executive functioning, such as verbal fluency, inhibition and decision–making skills, and these effects exist up to one year of abstinence (van Holst et al., 2011). Whether recovery occurs is largely unknown, although it appears that substitution therapy, in which the drug of abuse is replaced with methadone, is actually linked to cognitive decline itself (Davis et al., 2002; van Holst et al., 2011). Davis et al. (2002) concluded that at least some recovery is possible after abstinence. Gamma–hydroxybutyrate Gamma–hydroxybutyrate (GHB) is a central nervous system depressant drug that has been introduced in the late nineties. It is an odourless and colourless liquid, with a soapy or salty taste, it is often combined with alcohol and is also known as a ‘date rape’ drug. In the limited amount of research on the cognitive consequences of GHB, there are several studies that suggest negative effects. For instance, a double blind, placebo controlled study in healthy participants showed that GHB intoxication temporarily impaired working and episodic memory, in a dose dependent manner (Carter et al., 2009). It was recently studied that GHB–induced comas are associated with (verbal) memory impairments (Raposo Pereira et al., 2018a; Raposo Pereira et al., 2018b) and alterations in long–termmemory networks and lower hippocampus/ lingual gyrus activity while performing memory tasks (Raposo Pereira et al., 2018b).