Gouzoulis-Mayfrank E, Daumann J, Tuchtenhagen F, Pelz S, Becker S, Kunert H-J, Fimm B, Sass H (2000) J Neurol Neurosurg psychiatry 68: 179-725
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1) 28 regular ecstasy users who had either been using the drug at least twice monthly for six months or longer in the last two years, or had used E more than 25 times in the last two years. Excluded were those who regularly used other drugs, or were heavy drinkers. Most smoked cannabis to various degrees. The average total lifetime dose was 93 pills (3.5 per month).
2) 28 people who had never taken ecstasy before, nor any other drugs, and no regular heavy alcohol use
3) 28 people who had never taken ecstasy but did use cannabis matched with the ecstasy group. Again, no drug or heavy alcohol use.
Decreasing immediate verbal recall and working memory performance correlated with increasing lifetime doses of Ecstasy.
The study says: "These results raise the concern that ecstasy use, even in typical moderate recreational doses and possibly in conjunction with cannabis use may lead to a subclinical cognitive decline in otherwise healthy young people"