'The figure was low in 2003, 2004 too, with stricter enforcement by the police,' he said. 'But after a year or two, when the arrested got released, they returned to the drug market, pushing the figures up.'

The number of reported drug users has yo-yoed over the past 25 years - dropping to 16,314 cases in the late 1990s before climbing back to 18,513 in 2001. Throughout the previous decade, the figure dropped continuously until 2007, before peaking and dropping again, according to government figures.

'People take drugs because of problems with their family or other sources of pressure,' Chan said. 'If the government doesn't solve these deep-seated problems, the drug trend will only go up again.'

Dominic Lee Tak-shing, adjunct public-health professor at Chinese University, wrote a government-funded report on drugs policies in 2001. In that report, Lee argued that 'supply reduction executed at the border may be more effective than party and disco drug raids'.

A decade later, Lee said that 'nothing has changed' when it comes to the effectiveness of government policies.

'There's been no improvement,' he said. 'I've seen no victory by the government in winning the battle against drugs. It's a difficult battle.'

Indeed, the Global Commission on Drug Policy report declares: 'The global war on drugs has failed, with devastating consequences for individuals and societies around the world.'

The report, commissioned by former UN chief Kofi Annan and former US secretary of state George Shultz, among others, came out ahead of tomorrow's International Day against Drug Abuse and Illicit Trafficking.

The government defended its efforts: 'The fight against drug abuse is a protracted war,' said a spokesman for the narcotics division of the Security Bureau. 'We are pleased that the enhanced anti-drug measures have started to bear fruit.'

Those on the front lines also question whether the government numbers reflect the situation on the ground. The number of drug cases could be triple the official one, according to Bill Lee Kwok-biu, a social worker who specialises in drug rehabilitation.

Other 'worrying' trends also appear to be emerging, according to the experts.

Drug users in Hong Kong are younger, and more first-time drug users are girls, according to a South China Morning Post analysis of Central Registry of Drug Abuse data.

The government registry compiles reports from law enforcement bodies, welfare organisations and medical institutions.

More than 20,000 new drug users were reported in the past five years, with those under 30 accounting for over 80 per cent of cases - up from 65 per cent during the mid-1980s.

In 2007, the average age of first-time female drug takers was 15. Last year, it was down to 14. Males had a first attempt at age 15.

Among first-time drug users under 16, the number of girls taking drugs has now exceeded boys - last year, 209 girls and 180 boys were reported, reversing traditional trends.

'It's no doubt a worrying trend of more and more girls trying drugs,' says Professor Daniel Shek Tan-lei, chairman of the Action Committee against Narcotics.

College principal Chan said the number of his female students had grown from two 16 years ago to 29 now.

Experts said newly emerging soft drugs - like ketamine, the most consumed type in recent years - were changing the way people, especially females, perceived illegal substances.

'In the past, like 10 years ago, most people took hard drugs like heroin. But a poor image was often associated with these addicts, and females were discouraged from taking drugs at that time,' said Professor Lee.

'Soft drugs,' he continued, 'are seen as lifestyle drugs. Even celebrities and models are often arrested because of taking them.'

Ketamine has dominated the local drug market for years. Since 2001, it has become the main type of narcotic found on drug possessors who are under 21. Last year, ketamine addicts accounted for 75 per cent of all abusers under 21, outweighing the aggregate of other soft drugs like Ice, cocaine, marijuana and Ecstasy, according to government archives.

Scientifically, soft drugs, or psychotropic substances, will not turn abusers into addicts as easily as hard drugs, often referred to as traditional drugs. But social worker Lee said it was often not up to drug takers to decide what to consume.

'Initially, a young abuser starts with soft drugs, as he thinks these drugs are safer and not addictive,' he said. 'But later on, he may meet more drug dealers who will induce him to take hard drugs.' Why? 'Because he will get addicted and the trafficker can maintain a stable income from him.'

Drug abuse is higher in areas close to the border with Shenzhen, where teenagers can easily obtain drugs smuggled from the mainland, said Michael Luk Chung-hung, a Yuen Long district councillor.

Drug abuse in Yuen Long and the northern districts accounts for about a quarter of all reported cases in the city's 18 districts.

'I know the police have been doing a lot in Yuen Long, like searching units of public housing estates,' Luk said, though he agreed that more could be done.

Luk said it was time to consider implementing a compulsory, city-wide drug-testing scheme for students.

Yau Tai-tai, another district councillor for the worst-hit district, suggested extending the opening hours of public recreation facilities to deter youths from getting in touch with criminals during later hours.