CANNABIS is not benign and damages the development of children and teenagers’ brains, doctors have warned.

The LibDem 2017 manifesto contains a commitment to legalise cannabis arguing it would break the grip of the criminal gangs on the drug trade “and protect young people by introducing a legal, regulated market for cannabis”.

Canadian Federal politicians have also introduced a bill to legalise the drug to fulfil an election commitment to protect public health and safety.

But the interim editor-in-chief of Canadian Medical Association Journal urged MPs to oppose it arguing it will have an negative effect on the nation’s youth.

Dr Diane Kelsall in an editorial said: “Simply put, cannabis should not be used by young people.

“It is toxic to their cortical neuronal networks, with both functional and structural changes seen in the brains of youth who use cannabis regularly.

“The Centre for Addiction and Mental Health has stated unequivocally that ‘cannabis is not a benign substance and its health harms increase with intensity of use.’ “Although adults are also susceptible to the harmful effects of cannabis, the developing brain is especially sensitive.