Scientists have called for further research into the effect of cannabiscompounds on cancer cells after a teenage boy who was given the drug by his mother survived the disease.

Callie Blackwell said she decided to give cannabis to her son Deryn, who was suffering from a rare, aggressive form of leukaemia, to ease his pain and anxiety as he lay dying in a hospice.

After unsuccessfully requesting a prescription for a cannabis-based painkiller from a doctor, Ms Blackwell and her husband Simon met a dealer in a service station to buy some cannabis, which they prepared at home in a pressure cooker using instructions found online.

“I thought: ‘what have I got to lose? He’s dying anyway’. The effects of it blew my mind. It wasn’t what I expected,” Ms Blackwell told ITV’s This Morning.

Ms Blackwell said she expected 14-year-old Deryn, who had undergone multiple rounds of chemotherapy and radiotherapy following his diagnosis at the age of 10, to die when doctors said nothing else could be done.

But Deryn, who is now 17, made a gradual recovery and is now studying catering and has a part-time job as a vegan chef.

Cancer experts have warned stories like Deryn’s cannot prove the efficacy of one treatment over another until properly controlled clinical trials have taken place.

“There have been lots of studies looking at the effect of cannabis on cells growing in the lab, but that’s been quite mixed, it seems to have had different effects on different types of cancer cells,” said Emma Smith, science information manager for Cancer Research UK.

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Deryn Blackwell during his cancer treatment (Twitter / @_doeverything)