U.S. border protection has barred a young Canadian woman from crossing the border after cannabidiol (CBD) oil was found in her backpack — a non-psychoactive product of the cannabis plant she uses to treat the painful side effects of scoliosis.

The woman, who has asked not to be identified by CBC News pending the outcome of an application for reentry, is the latest Canadian to face border troubles after Canada legalized cannabis last year.

Thousands of Canadians have been denied entry to the U.S. simply for admitting they've smoked a joint once in their lives. Others have been banned from entering the country for life for carrying cannabis products to the border — a punishment that this unsuspecting CBD oil user could now face as well, according to immigration experts.

While some U.S. states have dismantled prohibition, cannabis possession remains a criminal offence federally and — like heroin — cannabis remains a controlled substance under U.S. federal law.

And the U.S. border is, of course, governed by federal law. Travellers are prohibited from carrying cannabis and its related products over the border — even after the federal government in Washington removed industrial hemp from the list of controlled substances in December 2018.

Pulled over for a secondary check at the Blaine, Washington crossing last weekend, the woman said she was asked by border patrol officers if she had any "leafy greens" on her person. The officer did not say the word "cannabis," she said.

"I said no because, to me, 'leafy greens' is like marijuana, the actual bud, things that you smoke, recreational drugs. I use CBD daily and it's not psychoactive, it can't get me high at the dosage that I've been told to take it at," she told CBC News.

A search of her possessions turned up a bottle of CBD oil — something she thought was perfectly legal to carry over the border, considering such products are legal in both British Columbia and Washington state.

"I didn't think anything of it. I just always have it on me because I take it daily and because of his wording, 'leafy greens,' I didn't fully understand that I needed to declare it," she said.

CBD oil is seen displayed at The Cannabis World Congress & Business Exposition (CWCBExpo) trade show in New York City, New York. A Canadian woman is facing a potential lifetime ban for carrying CBD oil to a U.S. border crossing in Blaine, Washington. (Mike Segar/Reuters)

A simple oversight en route to a friend's cabin could result in a lifetime ban on entering the United States for this woman, said immigration lawyer Len Saunders.

"There seems to be a lot of confusion with Canadians entering the U.S. with regards to CBD and THC and all the derivatives from marijuana," said Saunders, a Blaine-based lawyer. "From my experience, if anything is coming from the marijuana plant, even if it's an oil or a gummy candy, it seems to be grounds not only for inadmissibility and fines ... but also a lifetime ban.

"Even though she made an honest mistake, if the officers deem that she has a controlled substance with her, and she admitted to it, then she's inadmissible for the rest of her life. Even if she gets a waiver approved, she'll still have to go through a renewal every year, two years or five years."

The woman in question said she knew loose cannabis and joints are prohibited at the border — there are signs at the border warning travellers not to bring them — but she didn't realize the same rules apply to the CBD oil she uses for medicinal purposes.

She was fined $500 for failing to declare the oil, fingerprinted and subsequently denied entry to the U.S.

"I felt like a criminal and they seemed like, 'Oh, here's another pothead using this,'" she said. "I didn't feel like I was treated with respect on it, considering it's for a medical purpose."

U.S. and Canadian flags fly on the Peace Arch monument at the U.S.-Canadian border near Blaine, Wash., and Surrey, B.C., on Sept. 26, 2018. (Ted S. Warren/Associated Press)

She was sent away with a stack of paperwork — and an application for a special waiver through a new online portal called e-SAFE — that she must complete if she ever hopes to regain entry to the U.S.

The application, which costs $600, is required for all people denied admission to the U.S. after deportation or removal.

"It seems like a much more serious thing than anyone had ever told me when I was there at the border," she said.

The woman is a frequent border-crosser — a student at the University of Guelph who often travels to Detroit for concerts and shopping — and said she fears she may face a lifetime of border problems because of this incident.

I tell people, 'You're in the system for the rest of your life.' - Immigration lawyer Len Saunders

"In five years will it peter out, or will I have to continue advocating my whole life now because of this?" she said.

"I'm still really not sure what's going to happen. It's an issue I don't want to follow me around my whole life."

But it probably will, Saunders said. "I tell people, 'You're in the system for the rest of your life,'" he said.

And the waiver application process to gain reentry is an arduous one, he said. The U.S. government demands a criminal record check from the RCMP, letters of reference, a letter of remorse for past wrongs, proof of employment and documentation outlining a person's residence and work history.

In some cases, the border agency will require a drug screening test to show a person is not still using illegal substances.

"It's a lot of personal information that some people would prefer not to give to the U.S. government, but they have to if they want to have a waiver approved. It's not optional. It's required," he said.

When asked about CBD oil, a spokesperson for U.S. Customs and Border Protection said it's the responsibility of travellers to familiarize themselves with U.S. law before seeking entry.

"Marijuana and marijuana products are considered controlled substances under U.S. federal law. Travellers found in possession of controlled substances at U.S. ports of entry can face arrest, seizures, fines, penalties or denied entry," the spokesperson said in a statement to CBC News. "Requirements for international travellers wishing to enter the United States are governed by and conducted in accordance with U.S. federal law, which supersedes state laws."

Depending on the product, CBD oil usually contains only trace amounts of tetrahydrocannabinol (THC) — the principal psychoactive compound in cannabis — and typically does not produce any sort of high.

U.S. President Donald Trump signed a new farm bill into law last year that removed industrial hemp and its derivatives — including some forms of CBD oil — from the Controlled Substances Act, provided the THC concentration is not more than 0.3 per cent on a dry weight basis.

This move opened the floodgates for CBD-related products, with some popping up on the shelves of mainstream retailers like CVS, Walgreen's and Rite-Aid. CVS sells CBD-infused sprays, roll-ons, creams and salves in some 800 stores.

Cars from Canada line up to cross into the U.S. in Blaine, Wash. Immigration lawyers warn past use of cannabis could lead to Canadian travellers being barred from entry into the U.S. (Elaine Thompson/AP Photo)

Still, U.S. Customs and Border Protection has not yet finalized how the new farm bill provisions will be applied to travellers.

"In light of these changes, (Customs and Border Protection) is working closely with its Partner Government Agencies (PGAs) that have regulatory purview over Cannabis Sativa L. and its by-products to assess the policy and regulatory changes and verify all importation requirements that will be necessary as a result of the 2018 Farm Bill," the spokesperson for the U.S. border agency said.

In meantime, entry happens at the sole discretion of the U.S. customs officers on duty — and they have a lot of latitude to ask questions to determine the admissibility of a foreign national.

"(Customs and Border Protection) administers and enforces importation laws and regulations on behalf of its PGAs, and coordinates with them actively at the border," said the agency spokesperson. "Until this interagency regulatory process is complete, and updated requirements are finalized and disseminated, existing importation protocols and trade filing guidance will remain in place."