A review by NIDA scientists explains that "neurotoxicity" arguments were based on overdosing animals, and that similar effects are seen with SSRI anti-depressants:

Psychopharmacology (Berl). 2007 Jan;189(4):407-24. 3,4-Methylenedioxymethamphetamine (MDMA) neurotoxicity in rats: a reappraisal of past and present findings. Baumann MH, Wang X, Rothman RB. Free full-text: http://www.ncbi.nlm.nih.gov/pubmed/16541247

It has been previously claimed that overdoses of MDMA caused structural damage to serotonin axons ('axon pruning'), but there has never been any good evidence of this. Most evidence points to modulation of expression of serotonin transporters without damaging the axons themselves:

The Nature of 3, 4-Methylenedioxymethamphetamine (MDMA)-Induced Serotonergic Dysfunction: Evidence for and Against the Neurodegeneration Hypothesis. Biezonski DK, Meyer JS. Curr Neuropharmacol. 2011 Mar;9(1):84-90. Free full-text: http://www.ncbi.nlm.nih.gov/pubmed/21886568

Also, one particularly notorious retracted study mixed up MDMA and meth... http://en.wikipedia.org/wiki/Retracted_article_on_dopaminerg...

You were under a false impression if you're referring to a single recreational dose (approx 120mg) taken once or even twice a weekend. The studies on animals that are often pointed to in Wikipedia involve exposing lab animals to doses that are both quite high and importantly far more frequent than the way this drug would utilized during sessions or as a party drug. Controlled tests on lab animals where a more normal dose was given and a more appropriate period of time was given between the next dose do not show any compelling evidence of any kind of long-term anomalies.

The studies on humans that are often cited are typically unscientific because they're inclusive of individuals who also use other substances that are known to be neurotoxic such as alcohol or even methamphetamine. Also more importantly these recreational users are not given a supply of pure MDMA so it's safe to assume that some percentage of them are actually ingesting a cocktail of MDMA adulterated with other substances.

With all of this said, the verdict is still out on whether or not this is neurotoxic in human at normal doses.. there definitely is a long term tolerance that builds up to the effect of the drug but this alone does not prove anything about neurotoxicity.

Not entirely accurate. MDMA does cause certain permanent neurological changes. However, at therapeutic doses/regimines, there aren't any behavioral deficits that result from those neurological changes. There are also certain things you can do to decrease neurotoxicity.

I took a fair amount of the stuff back in the 1980s -- at one point I estimated my cumulative total consumption as around 15 grams. (I'm sure there are people far beyond that now.)

It is definitely neurotoxic -- I could tell that the first time I took it -- but in my experience, the noticeable effects are temporary, being mostly gone in a couple of weeks and quite undetectable after a couple of months. As a software developer who works in a fairly technical field, I'm quite sensitive to how well my brain is working on any given day. I did not notice any long-term falloff in my abilities as a result of MDMA use.

All that said -- it does invite abuse, and I was abusing it. In 1990, my then-SO left me, and I realized I had to quit.

I wouldn't worry about occasional, supervised, therapeutic MDMA use by healthy individuals.