I'm quoting an article here:

"There is a trend among regular ketamine users to cook up already dehydrated ketamine HCI into a finer, smoother powder. The theory behind this is that it not only makes it better to snort, but that it also yields stronger effects and is much softer on your bladder than the shard-like crystals. My friends and I have pretty much swallowed this theory as gospel over the years. In fact, I’ve sometimes wondered if cooking up the k is the only thing that’s enabled us to tolerate the drug without running into health problems. While I can testify that cooking k up makes the effects floatier and more enjoyable, I wasn’t convinced that it reduces the bladder damage. Was there any real science behind this claim?

I hunted down Dr. Karl Jensen to get the final word, straight from the horse’s mouth, but he really had nothing to say on the matter. Dr. Simon Baker has written a few papers on ketamine, but his area of expertise is very specifically its toxicity in the bladder. So he was happy to address my question with a simple no. Here’s what he had to say:

We have no evidence to suggest this process of rehydrating and then redehydrating the ketamine would affect its chemistry and therefore would not expect it to affect its bladder toxicity per se. A recent study demonstrated that this effect is to do with the binding of the drug, and nothing to do with its preparation. In one girl given a very large amount of ketamine daily iv in a hospital for chronic pain, bladder symptoms were reported so this is nothing to do with the size of the crystals. There is some potential that finer crystals, being more readily soluble, would enter the bloodstream faster causing a more pronounced spike in initial concentration and this might be expected to increase toxicity (and give the effects you describe). However, this spike in serum ketamine may not affect ultimate bladder ketamine concentration greatly as this builds up over a period of hours whilst the urine is retained.

So there we have it. The claim of making ketamine safer by cooking it up is a complete fallacy. It is an urban myth."