This is the worst thread ever. 99% of it is complete bullshit, and the parts that aren't bullshit seem to have contradictory statements from other people about the same chemical. Things like seizures, addiction, respiratory depression, short term memory loss, reduction of intelligence, psychosis, depression, vitamin B12 depletion, etc. are not signs of neurotoxicity. Dead neurons are. Brain plasticity is the reason that all of these drugs cause permanent psychological and physiological changes, just as every other aspect of your experience in life does.
Unless you have conclusive evidence from multiple studies that a drug causes NEURONS to DIE forever, that drug is not neurotoxic. Studies done in mice, rats, and monkeys are about the only ones that tend to universally apply to humans but at different dosage levels, and even then it's not always going to apply.
As far as I've seen, and I don't care to dig up and cite legitimate studies on all these because many links/citations are already included in this thread, only the following recreational drugs are proven neurotoxic in humans at some dosage level that might be taken by some recreational users:
ethyl alcohol
phencyclidine
amphetamine
methamphetamine
methylenedioxymethamphetamine
methylenedioxyamphetamine
4-chloroamphetamine
4-iodoamphetamine (if you call these haloamphetamines "recreational drugs")
4-methoxyamphetamine
Neurotoxicity is also not a sign that a drug is unsafe to use recreationally. Look at all the research done on people with extensive brain damage. Entire sections of the brain can be destroyed, and the brain can over time adapt and use areas not normally used for the functionality the destroyed area is used for in normal humans for these functions. The neural network in your head can map around the brain cells you kill having fun with drugs, and completely replace and maybe even improve upon the way it worked beforehand.