Researchers at Toronto's Hospital for Sick Children are poised to begin a clinical trial using cannabis extracts to treat children with severe epilepsy whose seizures can't be controlled with existing medications.

The trial is believed to be the first in Canada to test an oral preparation that contains both CBD and THC, compounds in marijuana that have been shown in the lab and through anecdotal reports to have anticonvulsant properties in children with treatment-resistant epilepsy.

CBD, or cannabidiol, is one of hundreds of active chemicals in the marijuana plant, many of them touted to have medicinal properties. THC is the psychoactive ingredient that produces the "high" associated with pot.

While research has found CBD to be effective in reducing seizures, there has been no rigorous study that's looked at the combination of CBD and THC, said pediatric neurologist Dr. Blathnaid McCoy, who will lead the clinical trial that begins early next year.

The Sick Kids study will enrol 20 children aged one to 18 with Dravet syndrome, a rare and debilitating form of epilepsy that begins in infancy. The condition, which is caused by a genetic mutation, accounts for about one per cent of all cases of epilepsy.

"It varies massively, but [children with] Dravet syndrome often have multiple seizures every day and they can have quite prolonged seizures," said McCoy. "And in line with that, they also have a significant disruption in normal development, so they can have challenges with their mobility, with feeding difficulty, with interactions.

"Certainly when the epilepsy is difficult to control and very treatment-resistant from early on, they can have catastrophic outcomes in terms of their development," she said.

Dawn Bellefeuille's youngest son Sean is one of those children.

He suffered his first seizure at two months old, and they grew worse and more frequent over time, said Bellefeuille, who has three older children who aren't affected by the condition.

Sean's seizures, which sometimes number 40 a day, have severely delayed his development. At 13, he is virtually non-verbal and can't dress, feed or toilet himself. He attends a special-needs school, but needs round-the-clock care.

"He's been on umpteen different drugs since he was born," Bellefeuille said from Ottawa. "He didn't take his first steps until be was four years old; he didn't sit up on his own until he was 18 months old."

Cannabis to be tested in kids with severe epilepsy - Health - CBC News