A South Australian couple have admitted conducting a medical marijuana trial on their seriously ill 12-year-old daughter.

Victor Harbor schoolgirl Tabetha Fulton suffers from a rare inflammatory lung disease, which prevents oxygen from being absorbed into her blood stream.

Her younger sister Georgia-Grace has the same condition, which requires the pair to be hooked up to an oxygen supply 24 hours a day.

The family turned to cannabis oil to reduce inflammation in Tabetha's lungs, after conventional treatments failed.

The huge amounts of medical steroids needed to help Tabetha breathe reached toxic levels and caused her to collapse at school in October last year.

Side effects included weight gain and depression.

In a fit of desperation her family sourced and used cannabis oil, which they mixed into smoothies.

The oil does not have any hallucinogenic properties and the Fultons claim the results were astonishing.

“I can surf, and I can go to school,” Tabetha told 9NEWS.

“I can do everything I want to do.”

The family has begun a campaign to have the treatment approved in Australia. but in the meantime, the family of seven will travel to Vancouver in Canada next month to continue the trial legally.

South Australia decriminalised minor cannabis offences in 1987, the first state to do so.

Residents found with up to 100 grams of marijuana, 20 grams of hash resin, one non-hydroponic plant or cannabis smoking equipment are fined between $50 and $150.

South Australian viewers can see the full story on 9NEWS at 6pm.