According to doctors at Tuen Mun and Princess Margaret hospitals, abuse of ketamine - the second-most abused drug in Hong Kong - may cause severe bladder dysfunction or even kidney failure.

It is the first time the drug has been linked to severe damage in vital organs, and it is also the first time such damage has been recorded anywhere in the world.

The doctors' report, to be published in the August issue of the Hong Kong Medical Journal, said they have detected severe bladder and kidney damage among 10 Hong Kong young adults, aged 21 to 30, who have abused ketamine for up to four years.

In certain cases, damage was so serious that patients could hold no more than 15 milliliters - or one tablespoon - of urine and needed to urinate every 15 minutes. One of the abusers also experienced acute kidney failure, where the kidneys cannot concentrate urine without losing vital electrolytes. Such failure is potentially life-threatening and requires intensive treatment.

These new problems might now be added to a long list of other harmful effects of ketamine abuse, including permanent damage to memory, IQ, impaired long-term function and respiratory or heart problems.

The study was initiated by Dr Peggy Chu Sau-kwan of Tuen Mun Hospital, who called other Hong Kong hospitals to see if they had found similar cases.

"Princess Margaret Hospital had three similar cases, and we combined research programs," Chu said, adding the study of this potential effect of ketamine abuse will continue. "The urinary symptoms are very stressful and diminish the quality of life."

Ketamine is also highly habit-forming, said Dr Kenneth Lee Kwing-chin of the Chinese University of Hong Kong, though it remains less potent than cocaine or heroin.

Though the study's findings are new, Lee cautions that clinical evidence beyond these 10 cases needs to be established to prove a link of causation.

"But, based on existing evidence, we can still use this study to warn abusers that there is another potential effect of ketamine abuse," he said.

As with some other medical problems caused by the drug, such as heart arrhythmias, the impaired renal and urinary functions can return to normal over time if abuse ends.

In spite of its extremely deleterious effects, ketamine - also known as "Special K" - remains a popular drug among youths. It ranks only behind heroin in terms of popularity and is known for its hallucinogenic properties.

A spokeswoman for the Narcotics Bureau said they hoped the new finding will act as a further deterrent to teenagers considering trying the drug.

"Most young people do not realize the extent of damage ketamine will do to their body," the spokeswoman said. "It's the right time to emphasize the serious harm this kind of substance will do to their health, and that the effects will be lasting and very damaging."

Ketamine is the leading abused substance among youth under age 21, she said.

Lee noted the 10 cases involved abuse of "street ketamine," which can often consist of up to 90 percent of other substances, including cocaine and marijuana, which can "definitely contribute to kidney and urinary failure."

The Hong Kong Medical Journal has decided to release an early online report due to the importance of the findings "for frontline doctors dealing with ketamine abuse around the world."

Ketamine abuse has made headlines in recent weeks, as police have discovered worrying evidence of growing abuse and trafficking.

Earlier this month five students, aged 13 to 17, were arrested at a Fan Ling secondary school for allegedly selling or taking ketamine on school grounds.

Four girls, aged 13 or 14, were hospitalized after taking the drug, and two boys were arrested on suspicion of selling the drugs to the girls.

The students were released on bail and ordered to report back to police early next month. No charges have yet been laid.

Earlier this week police also arrested a sixth suspect - a 15-year-old boy - in connection with the case. He has also been freed on bail.

Late last month police smashed a drug packaging and distribution center in a flat in Mong Kok, seizing HK$1.13 million worth of drugs, including 80 grams of ketamine, and arresting a couple.