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MDMA & Its Effects on Memory
An Overview of Current Research - 2/28/00
by Erowid

Does MDMA use cause long term disruptions in memory or other mental skills?

In trying to answer this, we looked at a collection of 7 recent studies which attempt to address this topic. A list of all the studies we knew of on this topic as of March 1, 2000 is shown below. It is frustrating for interested readers who examine the record on MDMA associated memory disruptions that much of the research seems to contain fundamental flaws which make it possible that all of the negative findings are a function of selection bias or other errors.

The data on the subject to date comes from Reneman, Morgan, McCann/Bolla/Ricaurte, Dafters, Parrott, & Krystal. Each of these researchers presents a small piece of a growing puzzle. Unfortunately the various research published by the McCann, Bolla, & Ricaurte lab contains very little of their actual data and instead includes only small samples of highly processed statistics. The reader is left relying on possibly incomplete, narrow, or incorrect analyses. We can't know because they don't allow anyone else to examine their results.

In some studies, little or no significant difference between MDMA users and controls were found, while in others seemingly dramatic memory or attention-task deficits were found. In Reneman's recent paper in Psychopharmacology, the MDMA users' short term memory scores all fell at or below the lowest score of the control subjects. In McCann's "cognitive performance" paper published in 1999 Psychopharmacology the 22 MDMA users' scores averaged 10-35% lower on several of the tests they were given, but the authors wrote "differences in cognitive function seen in MDMA users and controls were quite subtle, and only detected using a sensitive battery of cognitive tests."

In Bolla's 1998 Neurology paper (published with McCann & Ricaurte and presumably conducted in the same lab), the memory effects seem contradictory and the paper states that "when memory function in the two groups was compared without taking the average monthly MDMA dose into account, differences were not found." The researchers also showed that some of the heaviest users of MDMA had the best memory scores on one of the two tests.

In Morgan's 1999 Psychopharmacology paper, the heavy MDMA users studied averaged about 25% worse on both immediate and delayed recall tests, but he also found contradictory data. The heavy MDMA users who had abstained for at least 6 months before the test scored 10%+ higher than the controls (unfortunately due to the sample size this was only 3 people). Most of the heavy MDMA users studied had abstained for less than a month before the tests. Certainly we could chalk up any scores to individual variation, but the entire sample size for the heavy MDMA users is only 25. Perhaps all of the results can be accounted for by selection bias and individual variation.

The 1998 Parrott Psychopharmacology paper again showed that the 15 MDMA users had worse memory scores on 3 separate tests, but the problem with this and other attempts to study this problem is that the comparison group selection determines the outcome of the comparison and there is no actual 'control' group. This does not invalidate the results, but it weakens them.
What does all of this mean? Where we are in the winter of 2000:

  1. Most of the research published so far has been conducted by researchers attempting to show damage to memory or other attention-based mental tasts. Experimental bias in favor of finding deficits may affect the validity of the extrapolated results.

  2. The study sample sizes have all been very small and the subjects hand chosen by the researchers themselves. Despite *huge* populations of users available in every city of every MDMA using country, no broad based studies have taken place. Hopefully these will come soon to confirm or contradict the memory related risks.

  3. While the memory scores of MDMA users were shown by a couple of the studies to be between 20 and 50% lower than control subjects, the MDMA using subjects themselves did not report any decline that their memory or cognitive abilities. The researchers also report that even the heaviest of MDMA users do not show obvious signs of impaired.

  4. Some research has found there to be no significant difference in cognitive scores between MDMA users and controls.

  5. None of the research is prospective, all of it has been retrospective. No research so far has tested people's memories before and after their MDMA use to determine that it does, in fact, get worse. This means that the differences in scores could be part of a set of pre-existing differences. There could be characteristics which predispose certain individuals to want to use MDMA more heavily.

  6. In some of the research, the education levels of the subjects are matched poorly. In these cases, MDMA users are matched to controls with *higher* levels of education. This could result in a bias towards worse scores for the MDMA users.

  7. Less or no effects on memory and cognition are seen in moderate or light users of MDMA. The MDMA users who are found to have noticeably lower scores have generally been the heaviest users with total lifetime usage in the 200+ range, average dosages per session are often estimated at above 300 mg (up to a gram per day), sometimes using 6 or more times per month.

  8. Confusion between long term and short term effects of MDMA confuses the data. While most of the studies suggest their findings may show long term damage, they required only a very minimal (2 or 4 week) period of abstinence from use. Some MDMA users in the general population report feeling after-effects from single MDMA sessions for 2-4 weeks (or more). In order to reasonably make claims about long term memory disruptions, users should be studied after a minimum of two months abstinence if not more.

  9. Although most of the research does not address this, reported short term effects of MDMA use do include attention and memory disruption, as well as depression, mood swings, and other undesireable mental effects for some people. It is not at all hard to imagine that these effects might last for longer periods of time in some portion of those who use MDMA and might occur with more severity for those with extremely heavy use patterns.

  10. Articles in the press, comments by overzealous researchers, and statements by prohibitionist government institutions exaggerate the negative findings and certainty of their evidence.


Despite the uncertainty of and problems with the research published as of March 1, 2000, there is enough evidence to think that heavy MDMA use may cause medium or long term disruptions in short term memory and/or some types of mental fuction. The data so far is too weak to say for certain whether this is true or what percentage of users would be affected. Also, to date, the evidence may suggest that if MDMA use causes any memory or attention changes, the changes are subtle and are more likely the more frequent the use, the higher the dose, and/or the larger the lifetime total use. Unfortunately even the correlation between increased use and increased change is uncertain.

The data is far from conclusive, but certainly suggests caution for those who use MDMA regularly or heavily.