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.