Parents of children suffering from epilepsy say a recent move by Canadian border agents to seize shipments of medical marijuana oil from an American company could have a catastrophic effect on their children's health.

The families have sent letters to the federal government pleading for the border to allow shipments of Charlotte's Web, a type of marijuana oil that has been touted by some researchers as an effective therapy for hard-to-treat forms of epilepsy.

Charlotte's Web – named after a five-year-old Colorado girl with epilepsy whose condition improved after being treated with marijuana oil – has very low levels of the psychoactive ingredient tetrahydrocannabinol, but is high in cannabidiol, or CBD.

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Some scientists think CBD quiets the excessive electrical and chemical activity in the brain that causes seizures, although they say more research in needed.

The families say they have been purchasing the oil from CW Hemp, a company based in Colorado, where marijuana was legalized in 2014 and has since become a $1-billion industry. But the company notified the families late last month that it had stopped accepting Canadian online orders after "a drastic" increase in the number of shipments seized at the border.

Canada Border Services Agency said it is simply enforcing the law because marijuana remains illegal in Canada. The federal government has said it will legalize and regulate marijuana some time next year.

Alex Repetski uses Charlotte's Web as part of the marijuana oil he concocts at his Thornhill, Ont., home for his four-year-old daughter, Gwen, who lives with epilepsy that has left her developmentally delayed. The 42-year-old father claims the treatment has allowed his daughter to live seizure free for 20 months, and has helped her learn to walk and talk.

Repetski and other parents of children with epilepsy who use Charlotte's Web say Canadian companies do not offer a comparable product.

Not being able to receive the oil from CW Hemp "is a big problem," Repetski said.

"It's not allowing me to further tune her treatment in the hope and theory that she can do even better."

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The families have asked Health Canada for an exemption to allow shipments across the border.

Sylwia Krzyszton, a spokesperson with Health Canada, said families can either turn to marijuana oil made in Canada or individuals can apply for an exemption under the Controlled Drugs and Substances Act.

A spokesman CW Hemp said it hopes to resume shipping Charlotte's Web at some point.

"We are working in good faith with Health Canada to devise a solution so that we can provide our customers with Charlotte's Web in a manner that is expressly approved by the Canadian government," Ryan Kingsbury said in an email to The Canadian Press.

But time is running out for some families.

Elaine Nuessler said her four-year-old granddaughter, Kyla Williams, only has about a month's supply of Charlotte's Web.

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Williams, who lives with her mother and grandmother in Summerland, B.C., has intractable epilepsy and Nuessler said that while on prescribed medication, the girl would suffer more than 300 seizures per day.

Canadian marijuana oil helped for a period of time, but when it stopped working, Nuessler said they turned to Charlotte's Web. She said Kyla has been seizure free since turning to the American marijuana oil five weeks ago.

"Why would we actually change what's working? The slightest change can cause these children with epilepsy to go into seizures again," Nuessler said.

"Kyla's condition is life threatening should she start the seizures again."

Repetski and Neussler said they are now considering other ways to get the American marijuana oil should nothing change.

The parents of a 15-year-old girl with epilepsy who have also been purchasing Charlotte's Web from CW Hemp said they have found a solution, even if it's not legal.

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The couple, who live in Nelson, B.C., and who didn't want to be identified for fear of being prosecuted by authorities, said they now have their online oil order shipped to a friend in nearby Washington State. Then they drive there to pick it up and sneak it across the border.