HONG KONG, China (CNN) -- A 16-year-old Hong Kong boy makes two phone calls for delivery: One for pizza, the other for the drug ketamine. Two teenage girls are found semi-conscious in a car park after overdosing on ketamine. A 13-year-old boy joins a gang and is given free ketamine.





Glass capsules containing ketamine, which has become the drug of choice for Hong Kong's youth.





These are anecdotes told to CNN by police, a family doctor and a former gang member. Ketamine has become the drug of choice among young people, as the number of people under 21 taking drugs has surged 57 percent in the last four years in Hong Kong, said Commissioner for Narcotics, Sally Wong.





"We started off with a very small number of young people taking drugs. We are now more worried about the trend," Wong said. "We don't want a runaway trend; that's why we are stepping up action."





Ketamine, an animal tranquilizer, can put users in a dazed stupor for about two hours, doctors said. Long-term use of ketamine can impair cognitive function and damage internal organs.





An oversupply of the drug in Hong Kong and the fact that it is cheaper than other narcotics makes ketamine popular with young people, said Superintendent Wilson Fok of the Hong Kong Police Narcotics Bureau.





One gram of ketamine sells on the street here for $13 and is enough to be shared with two other people, while cocaine, for example, sells for $103 a gram, Fok said.





The drug is legal for medical use, but it is trafficked into Hong Kong from other parts of Asia, such as India and mainland China, and sold on the streets illegally, Fok said.





Police have recently stepped up their efforts to crack down on drug use at clubs and bars in Hong Kong and Shenzhen, a city in mainland China just across the border. Nearly 120 alleged drug users from Hong Kong, mostly under the age of 30, were arrested at entertainment venues in Shenzhen in July and held for 15 days in sweeps that made headlines for days here.





However, narcotics police said entertainment venues are not the only places they find drug abuse. "Forty percent of young people abuse drugs in public toilets and playgrounds. That's what our recent data from last year shows," Fok said. "They want to find some other places to take drugs."





The problem has gotten so bad that authorities have decided to do something never done here before: random school drug tests.





Beginning in September, some two dozen schools will conduct tests, as part of a trial program. Officials say the drug screening will most likely be in the form of urine tests, though they are still working out the details. Ketamine can be detected in urine for at least three days, doctors said.





Dr. Cheng Chi Man, a family practice doctor, runs a seminar that trains doctors to detect the signs of drug abuse in young patients: drowsiness, skin problems, frequent urination (ketamine can affect bladder function) and frequent sick leave.





"When we were 10 years old, we were still in primary school watching TV and eating candy. But they are now taking drugs."





Alman Chan, principal of Hong Kong's only drug rehab school for youth, the privately-run Christian Zheng Sheng School, said he has watched as drug use has grown.  See photos of the rehab school in remote Hong Kong »





"Just look at our school development. I was here 14 years ago. At that time, I was the only teacher. I had 18 kids. I only had one student who was 15," he said. "But now, I have one third -- about 40 of them -- who are 15 years old or younger. That shows you the number of students getting into drugs is bigger and also getting younger and younger."





There were a few reasons why children were getting involved with drugs, such as troubled homes and difficulties at school, he said. "People are
In what country is it most popular? What is the name of the drug rehab center for youth? What are the effects of the drug Ketamine? what is the top drug for young people in hong kong? how much has drug use increased in the last four years? how many arrests have been made? What is the top drug choice?
Hong Kong Christian Zheng Sheng School, put users in a dazed stupor for about two hours, ketamine, 57 percent 120 ketamine,
question: In what country is it most popular?, answer: Hong Kong | question: What is the name of the drug rehab center for youth?, answer: Christian Zheng Sheng School, | question: What are the effects of the drug Ketamine?, answer: put users in a dazed stupor for about two hours, | question: what is the top drug for young people in hong kong?, answer: ketamine, | question: how much has drug use increased in the last four years?, answer: 57 percent | question: how many arrests have been made?, answer: 120 | question: What is the top drug choice?, answer: ketamine,