Ketamine is known to produce pretty hallucinations and a feeling of ego-decentralization as well as unfortunate loss of motor control. But other than the uncomfortable feeling of 'brain freeze' what is known about the long-term effects of using this relatively unstudied drug? Well in the interests of harm-reduction, the results are coming in...
K-pains, which were anecdotal evidence of severe pain in the abdomen for chronic users is now known to be damage to the renal-urinary system. Ulceritive cystitis is a scarring of the nephrons in the kidneys and renal tubes from accumulation of the sharp blade-like crystals. Also thickening of the bladder wall can cause urination to be more frequent.
See the recent article "Cystitis due to the use of ketamine"
Chronic use is associated with a wide-range of memory and perceptual deficits, but long-term use can cause lasting impairments, particularly in episodic-memory (memory for events) and problems with attentional control.
See the article "Beyond the K-hole: A 3-year longitudinal investigation..."
Ketamine is seen as the currently most accurate pharmaceutical way of inducing a schizophrenia like state and is being used to understand how schizophrenia works and possible new treatments for it:
ketamine leads to the impairments in brain circuitry observed in both drug abusers and schizophrenic patients by causing increased production of a toxic free radical called “superoxide.”Which is no wonder such legendary K-heads like John Lilly started believing in delusions like he regularly communicated with space aliens, as it has been found that too much usage can make one superstitiously believe that there are meaningful connections between random events.
Ketamine was originally produced by Parke-Davis pharmaceuticals to replace the usage of the highly neurotoxic drug PCP. Black market buyers of 'ketamine' also have to be aware of the varieties of the equivalent of moonshine: bathtub-K, of which cheap and easily available dissociatives are substituted, like powdered DXM (Robitussen) and a wide variety of PCP variants.
All in all, good arguments for at least limiting any use of K to 'occasionally' I would think? My brain hurts....