Summary of Findings
Several years ago, JW Olney discovered that dizocilpine (MK-801), a chemical being tested to prevent brain damage from strokes, actually caused damage to specific areas of the brain in rats. Since this time, numerous other drugs in the same class (the dissociatives) have been tested, and they all share this problem. As some of you might know, I have spent a great deal of time trying to make sure that the Internet community, and the larger world, has detailed information about this complex, difficult-to-use, and often dangerous class of drugs. I first learned of Olney's lesions a few years ago, but it has taken me much time to review all the evidence, compare drug dosage within and across species, speak to heavy dissociative users, and so on. I am now ready to state my conclusions and make some recommendations, which are as follows (explained in detail in the full document).
Dissociatives definitely cause brain damage if used heavily.One sub-anaesthetic "line dose" of ketamine, an equivalent dose of PCP, or a third plateau DXM dose, is probably at least as damaging to your brain as a few day "bender" on hard liquor, and possibly more so because it affects specific areas of the brain.
The risk of brain damage is worse the longer you stay high at any given time; constant moderate-dose use is probably just as damaging as a brief, high-dose use.
Reaching the anaesthetic level is exceedingly hard on your brain.
Ketamine is probably the least harmful, PCP the most, and DXM somewhere in the middle, but this is a rough guesstimate. Nitrous oxide is brief acting, but it too may be dangerous; it is also known to damage both central and peripheral nerves by depleting vitamin B12
Some people may be more susceptible to Olney's lesions than others. There is, to my knowledge, NO way of knowing how susceptible you are.
In addition to brain damage, these drugs can also trigger psychosis, limbic seizures, temporal lability, depression, and other neurological and psychological diseases much more frequently than other types of drugs. The dissociatives can be highly addictive to a minority of users. In comparison, the marijuana and the serotonergic psychedelics (LSD, psilocybin mushrooms, peyote, DMT) are many times safer.
People who have used dissociatives heavily have shown clear evidence of brain damage. This is not necessarily conclusive, since the people who become addicted to them might have underlying conditions (specifically, temporal lobe complex partial seizures) which could be responsible for some of the damage. Nonetheless, I can't ignore the fact that most everyone who uses dissociatives both frequently and heavily ends up with some sort of neurological or psychological problem, ranging from impaired memory to a schizophrenia-like syndrome. Many of the impairments correspond exactly to the areas of the brain damaged in lab animals.
If you will not abstain from using dissociatives, there are several steps you can take to protect your brain, ranging from limiting frequency and dosage to taking nutrients and neuroprotective drugs. You can also use alternative methods (ranging from safer drugs to meditation) to reach the same places that dissociatives take you.