Lab tests at the University of Newcastle and Hunter Medical Research Institute found leukaemia cells were sensitive to a cannabis variety containing less than 1 per cent THC (tetrahydrocannabinol) - the psychoactive component commonly associated with marijuana.

The plant, known as "Eve", has high levels of the compound cannabidiol (CBD).

The three-year study was done in collaboration with biotech company Australian Natural Therapeutics Group (ANTG), which produces the cannabis variety.

"ANTG wanted me to test it against cancer, so we initially used leukaemia cells and were really surprised by how sensitive they were," Dr Dun said. "At the same time, the cannabis didn't kill normal bone marrow cells, nor normal healthy [white blood cells]. We then realised there was a cancer-selective mechanism involved, and we've spent the past couple of years trying to find the answer."

Dr Dun's team found that, for both leukaemia and paediatric brain stem glioma, the CBD-enriched variety was more effective at killing cancer cells than THC varieties.

"There are trials around the world testing cannabis formulations containing THC as a cancer treatment, but if you're on that therapy your quality of life is impacted," Dr Dun said. "You can't drive, for example, and clinicians are justifiably reluctant to prescribe a child something that could cause hallucinations or other side-effects.

"The CBD variety looks to have greater efficacy, low toxicity and fewer side-effects, which potentially makes it an ideal complementary therapy."

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