A quantitative meta-analysis was carried out on the chronic effects of ecstasy use on working memory (WM), assumed to consist of a central executive (CE) and four executive subcomponents: Updating, Attention shifting, Inhibition and Access to long term memory. Publications dating from January 1998 to January 2008 were only included when they fulfilled the criteria for a meta-analysis (number of subjects, means and standard deviations) and when polydrug users were used as controls. In addition, we also determined effect sizes for lifetime consumption differences between the groups of other psycho-active substances than ecstasy. Both Lifetime Total Ecstasy Consumption (LTEC) and the effect sizes for alcohol, nicotine, amphetamine, cocaine and lysergic acid diethylamide (LSD) were regressed on the mean effect sizes (mES)1 of the WM subcomponents in order to study dose-response relationships. Ecstasy users appeared to score significantly lower on the subcomponents Updating, Attention shifting and Access to long term memory, but not on Inhibition. We did not find significant regressions of LTEC on any of the executive functioning subcomponents mES values. Ecstasy users also consumed significantly more amphetamine, cocaine, alcohol, nicotine and LSD, but less alcohol than polydrug controls. However, also for these drugs no indications were found for a dose-response relationship with executive functioning.
Keywords: Ecstasy, working memory, meta-analysis, dose-response effects, Deterioration, declarative, short-term memory, perceptual, psychological functions, deteriorated, the visuo-spatial sketchpad, interchangeably, LTM, WM subcomponents, amphetamine, dose-response relationships, PSYCLIT, MDMA, DSM-IV, cocaine, nicotine, cannabis, psychoactive, homogeneity index, failsafe N, Polydrug Controls, alcohol consumption, Montgomery, Stroop negative priming, Morgan, RAVLT recall, non-inflated ES, neurotoxic effects, vulnerability, hypothesis, dopaminergic cells, methamphetamine, serotonergic neurons