Doctors in Hong Kong, where ketamine took off as a party drug about a decade ago, have recently found that heavy users have poor bladder control and are prone to long-term liver damage.

"The worst cases are in young people who have to empty their bladders every 15 minutes. They can't even take a bus ride without alighting and going to the toilet," said Ben Cheung, a psychiatrist who works with ketamine users.

"Their kidney functions are affected and they are so young. This is a serious health consequence that we never expected because it has never been seen anywhere else."

A recent study in Hong Kong of 97 drug users, most of whom primarily took ketamine, found that over 60 percent of them suffered depression, 31 percent complained of poor concentration and 23 percent had memory problems.

"It shocked the users. Never did they think it would affect brain function and they care about that," said Tatia Lee, who was a member of the team conducting the study.

POOR MAN'S COCAINE