Ketamine - popularly known as Special K - started out as a veterinary anaesthetic but has become increasingly popular as an illegal drug. It is popular in China, Hong Kong, Singapore and Malaysia and is increasing in popularity in Western countries. However, long-term studies are now starting to reveal its negative effects including poor bladder control, liver damage and kidney problems. A study of 97 ketamine users in Hong Kong also found mental-health problems: 60% of the sample suffered from depression, 31% complained of poor concentration and 23% had memory problems.
You can find out more about the long-term effects of ketamine at