The coverage, which requires employers to pay a premium, extends only to a handful of conditions as a last resort.

"It's not medical marijuana for any purpose," said Dave Jones, senior vice-president of group benefits at Sun Life. "It's for specific conditions and symptoms where the evidence is clear that medical cannabis has enough value to outweigh risks."

Sun Life's cautious approach reflects concern across Canada's health insurance industry over the potentially high costs of covering medical marijuana - in many cases higher than established pharmaceuticals - and thin clinical evidence for its efficacy.

Canada, a pioneer in approving medical marijuana, legalized recreational use this summer. Canadian insurers' reluctance to cover it suggests most patients here and elsewhere may continue to bear most of its cost despite pending legalization efforts worldwide.

Insurers' hesitance stems in part from the experience of agencies in Canada and other countries that have offered coverage and seen costs and usage skyrocket. And many doctors who commonly prescribe pot don't properly examine or follow their patients, said Cyd Courchesne, chief medical officer at Veterans Affairs Canada, which has covered medical cannabis since 2008.

"If I was working for any other company, and I was their medical director, I would say do not reimburse," Courchesne said. "We do not have enough information right now."

Cannabis research has been held back globally because most countries ban its use, making purchases for studies illegal or difficult. That's changing in Canada, where a booming marijuana industry and the government now finance medical research, including efforts to create cannabis-based pharmaceutical-like drugs.

Canada law allows patients to buy medical cannabis with money from health-care spending accounts, which are financed by employers, but insurance companies make their own decisions on coverage.

Some insurers are starting to cover pot in response to rising demand from employees of the firms buying their coverage. Grocery chain Loblaw last year became the first major Canadian company to ask its insurers to cover medical marijuana.

But insurers are treading carefully. Sun Life covers pain associated with cancer, multiple sclerosis, rheumatoid arthritis, HIV and palliative care for serious illnesses; chemotherapy-induced nausea; spasticity from MS; and anorexia due to HIV.

Green Shield Canada, Great-West Life and Manulife Financial Corp have said they are considering or planning marijuana coverage.

Manulife, which offers marijuana coverage for a few companies that requested it, recommends an annual reimbursement limit from C$1,500 to C$2,500 and covers only a handful of conditions, a spokesperson said.

Great-West expects to begin offering medical cannabis coverage this year, but only when confident it will both improve health outcomes and hold down costs for employers. The firm is particularly interested in covering marijuana when it might be more effective than addictive pharmaceuticals such as opioids, said Brad Fedorchuk, a senior vice-president.

Marijuana's often higher costs make it that much more important for insurers to scrutinize the conditions they cover, said Mike Sullivan, chief executive officer of insurance analytics firm Cubic Health.

For instance, Baclofen, a muscle relaxer also used to treat spasticity, costs C$28.82 for a ten-day supply. Health Canada has estimated the average daily dose of marijuana, also used for spasticity, at between 0.68 grams and 1.5 grams, with a gram costing about C$8.

"If you open the door to conditions like post-traumatic stress disorder, short-term sleep disturbances ... you start encompassing a lot more people," Sullivan said.

SURGING COSTS

Veterans Affairs Canada began covering up to 10 grams per day of medical cannabis for its members in 2008, with no limits on price or medical condition.

After costs surged to C$63.7 million in the year ended March 2017 from C$19,088 in fiscal 2009, the group limited coverage to 3 grams a day at C$8.50 a gram. Total reimbursements fell to C$51 million in the year ended March 2018.

The agency imposed limits to give patients a more appropriate dose, Courchesne said, but also considered costs.

Christine Gopner-Reinecke, a spokeswoman for Germany's AOK Bundesverband - the largest of the groups administering the nation's public health insurance - cited many of the same concerns on cost and usage.

As of May, AOK had approved 9,700 patients for medical marijuana, about two-thirds of its applications since Germany legalized medical marijuana last March.

"We just cover it because the government wants us to," Gopner-Reinecke said. "We wouldn't cover it if it was up to us."

The Canadian Medical Association has warned its members to proceed with caution, citing a lack of evidence supporting cannabis treatment. Jeff Blackmer, the organization's vice president for medical professionalism, said he authorized medical marijuana for two of his patients when all other treatments had failed, but had seen little improvement.

Research is also inconclusive on whether marijuana effectively reduces pharmaceutical drug use when both are incorporated into treatment, Courchesne said.

Some studies, including one conducted at the University of New Mexico, have found that legal access to cannabis may reduce pharmaceutical drug use in certain patient populations; but others, including one published in the Journal of Addiction Medicine, concluded that marijuana use increases the risk of prescription drug abuse.

PRESCRIPTIONS AND FEES

Another problem, Courchesne said, are doctors and organizations that prescribe marijuana with little scrutiny of patients' medical need, often advertising themselves as a source of pot prescriptions.

Doctors' visits and prescriptions for any drug are generally free to patients in Canada, covered by provincial governments. But groups such as OneOunce.com and the Green Doctor Network directly charge patients fees ranging from C$150 to C$295 for consultations leading to marijuana prescriptions.

The Green Doctor Network requires no documentation or referral, other than an online application form. The organization did not respond to requests for comment.

OneOunce.com offers both in-person and Skype consultations, and requires a diagnosis or referral from a family doctor or specialist who has prescribed pharmaceutical drugs, said Fiona Fry, who handles patient services. OneOunce charges fees, she said, because it uses private physicians who don't bill governments and they spend more than the usual 15 minutes with patients.

The Federation of Medical Regulatory Authorities of Canada expects physicians to authorize marijuana only for patients with whom they have an existing medical relationship and after in-person consultations, Chief Executive Officer Fleur-Ange Lefebvre said in statement.

National Access Cannabis contacts patients' doctors for their medical history before writing pot prescriptions, said Evan Loster, a senior manager. The service is needed, he said, because many traditional doctors won't prescribe marijuana.

"Many physicians don't feel professionally comfortable recommending a treatment they don't know enough about," he said.