TORONTO -- About half of pediatric doctors surveyed about cannabis say they've encountered a young patient who had used marijuana for a medical reason.

The questionnaire for the Canadian Paediatric Surveillance Program found 419 of 835 respondents had a patient who had used either authorized or unauthorized cannabis for some sort of medical relief.

The one-time study did not detail how many cases involved unauthorized use, the nature of the condition being treated nor the ages of the patients. But principal investigator Richard Belanger says he's surprised by the number of young cannabis users and says it points to the need for more information for doctors, parents and patients.

The Quebec City pediatrician, also a professor at Laval University, notes that more than a third of respondents -- or 316 doctors -- said they had been asked by a parent or adolescent patient to prescribe cannabis.

Only 34 doctors said they had done so, with many expressing reservations about efficacy, impacts to developing young brains, and concerns about abuse and dependence.

The one-time survey was conducted in the spring of 2017 as part of the surveillance program's larger look at a host of hot-button issues including Lyme disease, Zika virus and eating disorders.

Belanger says researchers were surprised by how many kids and adolescents appeared to be turning to medical marijuana: "We thought it was less than that."

"We really want to make clear that cannabis is not only an adult issue, either for recreational but (also) medical purposes," Belanger said of the findings.

"Sometimes when we look at treatment we tend to forget kids and it should not be the case."

He suspected younger kids received authorized use for conditions including refractory seizures, cerebral palsy, and chronic pain, while adolescents were more likely to be unauthorized users and to treat other conditions "such as sleep problems or anxiety."

Belanger says the higher-than-expected usage could also be because the doctors surveyed generally treat kids with chronic and severe conditions that may require alternative treatments, and because most respondents came from urban and academic centres more likely to handle severe cases.

The survey response rate was also just 31 per cent, which "may under or over represent the knowledge and/or experiences of Canadian pediatricians," said the study, released Thursday.

Still, the findings raise questions about how impending legalization of recreational marijuana could impact unauthorized medical use.

"We're a bit anxious regarding that," said Belanger, pointing to "mixed perspectives" among doctors.

"From a pediatric perspective there's seldom reason to authorize cannabis and maybe seizure is one of them but still, there's no clear, no big evidence regarding that."

The survey found a clear majority of respondents had no knowledge or minimal knowledge on why cannabis might be prescribed for a child or youth and what products and dosages may be authorized.

"Paradoxically, they have a fairly positive view regarding cannabis use for medical purposes for certain conditions, despite the lack of solid scientific evidence regarding its safety and efficacy," said the survey, noting that could be due to difficult cases with limited therapeutic options.

Although medical marijuana has been legal since 2001, many questions remain, says Belanger: "It's a burning issue."

"There's a large space for the (Canadian Paediatric Society) or any other association or authorities to give more information on what are the clear facts regarding the possible benefits and the likely adverse events that can be related to medical use of cannabis."

Belanger notes the data was gathered prior to the publication of a pivotal study evaluating the use of cannabidiol (CBD) to treat epilepsy among children with Dravet syndrome reported in the New England Journal of Medicine in the spring of 2017.

Still, he bemoans a dearth of material to offer guidance. While more studies are underway, he says they mostly look at CBD and its effects on seizures and severe conditions.

"There are still problematic issues of studying cannabis with kids," notes Belanger. "I won't counsel anyone from entering a study exposing someone to cannabis if they don't have severe conditions.... On the contrary, in the adult field there are many more studies regarding cannabis either for pain related to arthritis, pain related to fibromyalgia, or spasticity regarding multiple sclerosis."

In the meantime, many parents and adolescents are asking for cannabis prescriptions.

"I think that everyone right now is aware that cannabis is not a simple thing," said Belanger.

"When someone starts using cannabis for a long period of time at an early age, it's probably at that time that the greater impact is likely. But at the same time, if your kids have seizures several times a day, what's the worse issue? It's kind of a tricky question for parents."