Citations needed. I have used multiple grams of ketamine in a single day and I don't think that it caused me any permanent harm. I have gotten K-pains and they are god damn horrible and feel like being shot in the gut or having an ice pick shoved up your dick, but they go away with no recognizable lasting harm. I know a lot of ketamine users who easily go through a few grams a day and none of them are likely to report that they have suffered from permanent harm. There is some evidence that some people can possibly have bladder damage caused by ketamine binges, although it isn't clear if this is directly related to ketamine or to impurities in clandestinely synthesized batches. Of course there is the risk of Olneys lesions as well but those are inconclusive in humans. Ketamine certainly greatly impairs all forms of memory, particularly it massively impairs visual-spatial memory due to inhibition of the hippocampus, but I have never seen any evidence that this is permanent. In some cases ketamine induced memory impairment is long lasting, but I don't believe I have ever heard of it lasting longer than one year.