Peter Reynolds of ‘Cannabis Law Reform’ declares hotly that it is a bare faced lie, with “no medical, scientific or any sort of evidence”, to say that cannabis causes brain damage.

Truly, there’s none so blind as those who will not see. For everyone else, however, they need only go on-line and Google the words ‘cannabis research on drug harm,’ to find a whole raft of medical and scientific evidence from eminent British and international research teams.

For example, the 2014 report of Professor Wayne hall, a drugs advisor to the World Health Organisation and professor of addiction policy at Kings College, London, having reviewed all the research of the last 20 years, concluded definitively that cannabis was highly addictive, wreaked devastation on the developing brains of young people and opened the door to hard drugs.

Nine years ago a survey of illegal drug use in the UK revealed that cannabis was being used by 13 per cent of people aged between 16 and 25.

Sweet old herbalists from the 1960s who giggle about how the occasional ‘spliff’ in their youth never did them any harm, are missing the point: today’s youngsters are into far stronger smokes, such as ‘skunk’ cannabis.

Again, last autumn’s report from the National Institute on Drug Abuse, showed how powerful ‘skunk weed’ causes significant damage to vital nerve fibres linking the two halves of the brain, which impaired a broad range of functions in adolescents, like memory, learning, and impulse control. These findings confirmed a large study conducted earlier in New Zealand, which had found that those who use cannabis heavily as teenagers lost an average of eight IQ points - the equivalent of going from average intelligence to the bottom third of the population. And the loss was permanent.

Medical and psychological studies are currently seeking to understand why and how the chemicals in the cannabis plant also seem to trigger schizophrenia and violent psychosis.

The above studies, and many others, provide one explanation so many young people seem to gradually lose their abilities and end up achieving much less than anticipated, or even being able to hold down a relatively simple job. Some people nevertheless believe that none of this matters. Mercifully, they are in the potty minority.

VICTORIA GILLICK

Wisbech