Overdosing on MDMA can cause serotonin syndrome, which can cause neuronal death due to excitotoxicity.
I was surprised to learn the US Military resurrected MDMA in the 50's and then in the 70's Prof Alex Shulgin got hold of it. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3931692/
Other country's handled it differently. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6435835/
But it does lend credence to the conspiracy theory that the British security services started flooding the football terraces to reduce the football hooliganism that was blighting the British isles, as "documented" by later films like Football Factory starring Danny Dyer and many more.
Still without it, would the world have what the US call EDM and what others call the Rave culture?
If they experienced serotonin syndrome it was quite easy to just point at the reported seratonergic substance that had been ingested (and which also may not have been present at all, depending on the source).
However, the same is repeated in literature about plain methamphetamine, not just methylene-dioxy-methamphetamine, so I would not entirely trust the current state of science on this.
I trust specific doctors who specialize in psychedelic medicine and psychiatry who have deep understanding of the metabolic pathways and pharmacokinetics of these substances.
https://www.pharmacytimes.com/view/serotonin-syndrome-myths-...