The survey was conducted between February and October this year by the HKCS' Prevention and Rehabilitation Services for Substance Abusers (PRSSA).

Close to 70 per cent of respondents - clients of the service - had taken the drug outside of parties.

More than half did so at friends' or their own homes, with more than a third taking the drug in karaoke lounges.

'That's because ketamine, unlike Ecstasy, does not need music to get one into the mood,' explained Rainbow Cheung Kam-hung, PRSSA service supervisor. 'Once they are hooked, they consume it anywhere.'

Another cause for alarm is that one-fifth of respondents are students, the youngest starting at the age of nine.

'Each of them is in touch with hundreds of others in school. Will they pass on their (drug-abusing) behaviour?' Ms Cheung asked.

Half of the respondents said family members were aware of their drug abuse, but many were lenient because they believed ketamine was less harmful than heroin or Ice.

Contrary to the popular myth, however, ketamine is addictive, with brain damage occurring in the long run.

Often sold in an impure form containing Panadol, rat poison, Ice, Ecstasy, Mandrax and other drugs, ketamine can also cause unexpected health problems.

Yee, 21, is a witness to its danger. Three years ago, she was given a pack of ketamine for free at a discotheque.

Having taken Ice, cannabis and heroin without getting hooked, Yee, who does not wish to be identified by her real name, began with one pack per day.

Within six months she needed more than 20 a day, costing about $1,000. She had to borrow from friends and sometimes steal from her parents.

Symptoms such as severe weight loss, breathing difficulty, stomach ache and urinary tract infection also emerged.

'At first, it did make me happy. Then I got bored without it,' she recalled.

'But when I had to always worry about where to get money and ketamine, I became more depressed after taking the drug.'

Now that Yee has been off drugs for five months, most of her ailments have disappeared, except the urinary tract infection. In fact, more than a quarter of respondents have suffered from this disease.

A link between ketamine abuse and the infection had yet to be made, said Dr Stephen Ng Wai-man at Kowloon Hospital's Substance Abuse Clinic.

'It could be because of unsafe sex during drug abuse,' he said. 'Perhaps the impurities in ketamine change the acidity of urine, making the abuser more susceptible to infections.'

Yee has seen symptoms of brain damage, such as slow reaction, loss of memory and depression among her drug-abusing friends. One killed himself a few months ago.

She is determined to stay clear of drugs. 'I will never get close to that group of friends again,' she said.