Three leading medical groups have withdrawn their support for an anti-drug campaign mounted by Health Canada, saying it has become a partisan exercise, not an educational one.

"We did not and do not, support or endorse any political messaging or political advertising on this issue," the College of Family Physicians of Canada, the Canadian Medical Association and the Royal College of Physicians and Surgeons of Canada said in a joint statement. Between them, these groups represent all 80,000 Canadian doctors.

Health Canada recently unveiled plans for a $5-million advertising campaign that will focus on telling young people about the dangers of marijuana and prescription drugs.

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The CFPC, CMA and RCPSC initially signed on as "partners" for the initiative.

But on Friday, Liberal leader Justin Trudeau lashed out at the campaign, saying the government of Stephen Harper was using tax dollars to attack him and his party's position in favour of decriminalizing marijuana.

"We know that Canadian taxpayers are getting extremely frustrated with the fact this government tends to use public money for ads that do more for its partisan aims than for actual public service," Mr. Trudeau said.

Almost immediately, the physicians' groups said they were withdrawing their support, but said they will continue to educate the public on the dangers of drug and alcohol abuse.

Health Canada, for its part, defended the campaign, saying: "The prevalence and health risks of marijuana and prescription drug use and abuse make them compelling public health issues in Canada. Marijuana is the most widely used illegal drug among Canadian youth today."

Health Canada said it routinely works with partners in the health sector and dismissed suggestions that the campaign is in any way partisan.

"The intent of the campaigns is educational and the material is based on evidence and science."