Cognitive deficits and cognitive normality in recreational cannabis and Ecstasy/MDMA users.

A crucial topic for recreational drug research is the long-term effects of regular usage. With respect to cannabis, Solowij et al. (2002) noted: ‘One issue remains unresolved: does heavy, frequent or prolonged use of cannabis lead to a deterioration in cognitive function that persists well beyond any period of acute intoxication? Is the functioning of the brain altered in the long-term?’. Many empirical studies have found selective cognitive deficits or altered brain activity in abstinent cannabis users (Loeber et al., 1999; Pope and Yurgelun-Todd, 1996; Solowij, 1998; Solowij et al., 2002), although there are also reports of unimpaired cognition (Lyketsos et al., 1999). This has led to a lively debate on the role of factors such as dosage, duration and intensity of usage, residual effects, pre-drug intellectual ability, and age at which regular usage commenced. Although there is an extensive body of cannabis research, many of the issues surrounding the neurocognitive deficits in recreational users remain unresolved (Pope et al., 1995, 2001a; Solowij et al., 2002). Ecstasy or MDMA (3,4-methylenedioxymethamphetamine) use has increased considerably in recent years, so that it is now second in popularity to cannabis (Pope et al., 2001b). Despite the comparatively brief history of Ecstasy/MDMA research, there is a now an extensive literature describing selective neurocognitive deficits in abstinent users (Fox et al., 2001, 2002; Gouzoulis-Meyfrank et al., 2000; Morgan, 2000; Parrott, 2000, 2001; Rodgers, 2000). Significant deficits in memory and other cognitive functions have been reported by groups from Australia, Canada, Germany, Italy, the Netherlands, Spain, USA and UK (Table 2 in Parrott, 2001). Indeed every study cited in two recent reviews reported significant deficits on at least one memory task (Morgan, 2000; Parrott, 2001). But does this apparent consistency in the empirical literature mean that the recreational use of Ecstasy invariably leads to cognitive decline, or do some users remain cognitively unaffected? In many studies the lighter Ecstasy users display unimpaired neurocognitive profiles (Fox et al., 2001; Rycroft and Golding, 2002; Turner et al., 1998, 1999), and only a minority of novice users complain of memory problems which they attribute to Ecstasy (Parrott et al., 2002). Our understanding of the long-term effects of cannabis is based upon an extensive empirical literature, describing a mixture of significant and non-significant findings (Lyketsos et al., 1999; Pope et al., 1995, 2001a; Solowij, 1998; Solowij, et al., 2002). The recreational use of Ecstasy is also associated with a wide range of cognitive and psychobiological problems (Morgan, 2000; Parrott, 2001). The topical question for Ecstasy researchers is not whether these deficits occur, but the conditions under which they develop and endure (Morgan et al., 2002). As noted above, neurocognitive and psychobiological deficits are often evident in the heavier Ecstasy/MDMA users (Fox et al., 2001; Morgan et al., 2002; Parrott et al., 2001, 2002), but there is a need for more empirical data on novice or light users (Rycroft and Golding, 2002). Researchers who find unimpaired performance profiles should be encouraged to submit their findings for publication; although obviously this would be facilitated by the inclusion of a heavy user group as ‘verum’ or positive internal control. It is crucial to document the conditions under which cognition remains unimpaired, just as it is important to describe the situations where deficits develop. There are numerous factors which may be important in this regard: gender, dosage, frequency and intensity of use, parallel use of co-drugs (especially other illicit stimulants and hallucinogens; Scholey et al., in press), overcrowding, hyperthermia, the use of putative neuroprotective agents such as fluoxetine, and genetic variations in MDMA metabolism (Tucker et al., 1994: Parrott, 2001). The animal literature