The mandatory drug-testing scheme would not allow police to override human rights, a drug control adviser said yesterday.
But restricting enforcement would mean that fewer drug users would be caught, said Professor Daniel Shek Tan-lei, the chairman of the government's Action Committee Against Narcotics.
"We'll start off with being a bit tighter for now, and we would like to raise this issue for the public to think about," he said in a television interview discussing the four-month consultation period on the scheme, which begins on Wednesday.
"Don't be mistaken, we hope to find drug users early, not to prosecute them but to help them."
Shek is looking for public opinion on two especially controversial points - what ages the scheme should cover and what objective standards should be set in enforcing it.
Now, police can only test people found with drugs. This means, for example, they cannot take action against young people who appear stoned at entertainment venues if they do not actually have drugs on them.
Shek said testing would only be carried if there was reasonable suspicion, which should be defined by objective standards, such as someone not being able to state their name.
"We don't want the public to feel that police have too much power, that overrides human rights. But if it's tighter, then there will be fewer prosecutions," he said.
Concerning age, Shek said: "If we can only take action on those under 21, it would be like singling out young people, and we think that's problematic.
"Maybe we should consider whether this scheme should be applied to all people," Shek said, adding that Hong Kong should not go down the path of "harm-reduction", such as setting up drug safe houses, as that would be surrendering to drugs.
Ben Cheung Kin-leung, chairman of the action committee's subcommittee on treatment and rehabilitation, said: "When we identify drug abusers, we won't prosecute them immediately. We'll refer them to social welfare organisations to follow up on them.
"If they're able to quit, we'll let them go. If they continue, then we'll consider prosecution."
The aim of the mandatory drug-testing scheme is to identify drug abusers at an early stage, as recent figures show they now stay hidden for longer compared with in the past.
The average time a person had been using drugs before being detected by the authorities was four years last year, compared with just less than two years in 2008.
"Four years means their body will already be substantially damaged by drugs," Shek said.