Health Canada has significantly expanded its medical marijuana manual for health-care professionals, adding major new sections about the potential adverse effects on the teenaged brain and driving safety.

The document is much larger than the previous 2013 edition, and responds to doctors' complaints about having too little information on the medical science even as they're being asked to authorize marijuana for a growing number of patients.

Dr. Cindy Forbes, a family doctor in Fall River, N.S., and president of the Canadian Medical Association, welcomes the new science in the guide. (Canadian Medical Association) The heavily revised manual arrives as the Liberals sort out how to legalize recreational marijuana as promised in the federal election – and the document's fresh litany of cautions may provide ammunition to opponents.

CBC News obtained a draft copy of the 158-page manual, dated Dec. 23, 2015, and due to be published this spring, under the Access to Information Act.

The document replaces a three-year-old, 94-page document, and features an "adverse effects" section that is more than 50 per cent longer than its predecessor. The section reviews in greater depth whether cannabis may affect the onset of schizophrenia or psychosis, among many other medical issues.

The older manual also referred only to dried plant, while the new one cites fresh marijuana and oils, which are also now available under a new commercial regime consisting of 30 Health Canada-approved growers shipping to about 37,000 patients. The document also features a new section on vaping, that is, cannabis electronic cigarettes.

New sections on dangers

Like the old document, the expanded "Information for Health Care Professionals" is prefaced with a boldface warning that "it should not be construed as expressing conclusions from Health Canada about the appropriate use of cannabis … for medical purposes."

A section on adolescents has been added to a chapter on fetal and child development; there's new information on "sperm and testicular health;" a new section on depression; more information about therapeutic uses to relieve epilepsy; and five new pages on cannabis and driving.

Health Canada began working on revisions to the medical marijuana guide under the watch of then-health minister Rona Ambrose, now Conservative interim leader. Ambrose is a staunch opponent of the legalization of recreational marijuana. (Sean Kilpatrick/Canadian Press) "Studies have shown that acute cannabis administration (ie. THC) affects areas of the brain involved in perception, attention, concentration, inhibitory/impulsivity control, executive control/decision-making, awareness, alertness, and co-ordination all of which are required to safety operate a motor vehicle," says the expanded version.

The language is dense and the tone balanced, often citing conflicting research and cautioning against hard conclusions, with hundreds of detailed citations throughout.

A spokesman for Rona Ambrose, former health minister and now the Conservative party's interim leader, says she did not direct the department to produce the new manual, whose revisions were begun under her watch. Ambrose has been one of the most outspoken opponents of the Liberal plan to legalize recreational marijuana, which a task force is now considering.

The information is going to be useful in general. - Dr. Cindy Forbes, president of Canadian Medical Association

"While the update may have been initiated while Ms. Ambrose was still the health minister, it was not done as a result of any direction from her‎, but rather by non-partisan public servants at Health Canada," said Mike Storeshaw.

"Any additional cautions or warnings would therefore reflect the submissions and evidence they received from the medical community, which have been significant in many cases."

The president of the Canadian Medical Association, Dr. Cindy Forbes, said she welcomes the new manual, especially any new research on cannabis and adolescents.

"We're very concerned about the young developing brain and nervous system, and so if there is new information or clarity around guidelines in this area, it will be welcomed," she said from Halifax, adding that the science can help inform Canadians about recreational marijuana as well.

"I think the information is going to be useful in general."

A spokesman for Health Canada, Sean Upton, said the document reflects international research carried out since the 2013 edition, with sections on potential therapeutic uses of cannabis as well as harmful effects. He said the new evidence about cannabis and youth will also help inform the task force on recreational marijuana.

Input to task force

"The government of Canada has committed to legalizing, strictly regulating and restricting access to marijuana to keep it out of the hands of youth," Upton said.

"Keeping marijuana out of the hands of youth is strongly supported by this evolving evidence base. This and other evidence will be an important input to the task force mandated to examine the issues related to the legalization and regulation of marijuana, and which will consult broadly with experts in public health, substance abuse and law enforcement."

Liberal MP Bill Blair, parliamentary secretary to the minister of justice, is in charge of a task force examining how to implement his party's promise to legalize recreational marijuana, for which there is no hard timeline. (Sean Kilpatrick/Canadian Press) Health Canada maintains an "adverse reaction" database for drug companies, consumers and others to record incidents involving pharmaceuticals and other substances, including medical marijuana.

Of some 45,000 reports registered in 2014, the first full year in which accredited marijuana firms were required to report adverse incidents, just four cited medical marijuana. Only nine such reports were registered in 2015, with unwanted side effects including paranoia, asthma and dizziness, none of them serious. The database includes voluntary reporting by doctors and patients.

Health Canada issued its first, much slimmer, medical marijuana manual in 2003.

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