OTTAWA -- The Harper government's resolve to enforce the law against marijuana use is unshaken by a call to legalize pot from the country's largest mental health and addiction treatment centre.

Justice Minister Peter MacKay said Thursday the Conservative government has no intention of heeding the call of the Centre for Addiction and Mental Health.

Indeed, the government remains committed to going in the opposition direction, said MacKay: finding ways to actually increase enforcement of marijuana laws, including potentially making it a ticketing offence to possess small quantities of dope.

But Liberal Leader Justin Trudeau, who has been championing legalization for more than a year, said CAMH's endorsement of the idea shows he's on the right track while the Tories are ideologically bound to a war on drugs that has proven a total failure.

NDP health critic Libby Davies, whose party supports decriminalization of marijuana, said the Conservatives are becoming increasingly isolated on the issue as more and more public health groups refuse to back their tough-on-pot message.

In a policy statement released Thursday, CAMH said cannabis should be legalized and strictly regulated, sold through a government-controlled monopoly with limited availability and an age limit. The centre concluded that the current legal prohibition on pot has failed to prevent use or reduce the harm it can cause.

That pretty much echoes the arguments that have been made by Trudeau, who has been pilloried by Conservatives for allegedly wanting to make pot more easily available to children.

"Yes, it's nice to see a world-class organization like CAMH come out and agree with (us) and demonstrate that we're on the right track," Trudeau said in an interview.

By contrast, he said CAMH's position shows the Harper government is "trapped in policies based on ideology rather than policies based on evidence and that is harmful to Canadians and to Canada."

MacKay, however, was unmoved.

"It surprises me, quite frankly, because there are just as many respected organizations and credible reports that say the opposite," MacKay said on his way into a committee meeting.

He argued that other public health groups have warned about the negative impact of marijuana on the developing brains of children and the fact that it can "trigger episodes of psychosis and schizophrenia and other serious mental conditions."

"And so I think there is a need to really be very circumspect about any move towards making marijuana more readily available. So that certainly is our government's position. We do not intend to legalize or decriminalize."

MacKay added that the government continues to consider "methods in which we can increase enforcement," including the ticketing option favoured by chiefs of police.

"This would not decrease but increase enforcement and optionality for police to ensure that people are respecting the law," he stressed.

Trudeau argues that legalizing and strictly regulating marijuana would do more to restrict availability and reduce consumption, particularly among young people, than the failed war on drugs.

He said Thursday that he has deliberately not spelled out precisely how a regulatory regime would work because he wants the input of experts and groups like CAMH.

On that score, Trudeau said he's "very interested" in CAMH's advice that advertising, marketing and sponsorship by marijuana producers should be prohibited and that health information should be clearly displayed.

Davies said CAMH brings "a lot of credibility" to the debate on marijuana because it so well respected.

While the NDP has not gone as far as the Liberals in calling for outright legalization, Davies said New Democrats see decriminalization as a first step, to be followed by a serious public debate on what more needs to be done.

The "biggest impediment" to that debate, she said, is the ruling Conservatives, "who've buried themselves in this rhetoric of the war on drugs, when I think most Canadians know it's absurd and it's unrealistic."

The rigidity of the Tories' position "does leave them more and more isolated on the question," Davies said.