I only know hearsay, but the issue effects those sniffing 2-3+ grams a day, every day for extending periods. The ketamine causes internal scarring of the bladder / urinary tract (not sure which or if either), that scarring stops the organ (maybe wrong word) from expanding and contracting.

So you feel like you need to piss regularly, but only a few drips come out. The damage can get so severe bladder gets removed.

At the lesser end of the damage is agonising stomach cramps, no idea what the cause of this is.

source: spent too long in the uk freeparty rave scene when ketamine was legal and people assumed it was completely safe due to lack of come down. Too many people ended up with severe ketamine addictions and many have to know piss through a bag