Select Committee on Home Affairs Memoranda


Submitted by Mary Brett, Dr Challoner's Grammar School

  1.1  As a biology teacher and head of health education of 27 years in a large State Grammar School for Boys, I have watched with mounting alarm the growing clamour for the decriminalisation of cannabis. My main concern is how cannabis affects the brain, particularly the processes of learning and memory and the personality of the user. I have witnessed these detrimental effects in some of my pupils.

  1.2  Decriminalisation would inevitably increase use—it always does! Even if use were restricted to the over 18s, (cannabis like alcohol is an intoxicant), school children would still be targeted, and access would be made easier for them through older siblings. Surely under-age drinking has taught us something!

2.  How Drugs Work in the Brain

  2.1  Messages pass along the nerve fibres as electrical impulses and cross the gaps between nerve cells as chemicals (neurotransmitters). These are the brains natural "drugs", each having a particular shape to fit the receptor site on the membrane of the next cell, rather like a key fitting a lock. Unfortunately, the brain cannot distinguish between these neurotransmitters and the "mind altering" drugs that people take. Cannabis mimics the neurotransmitter anandamide (ananda: Sanskrit for "bliss") to give the "high". It also occupies the same receptors sites as the opiates—possibly explaining its pain control properties. The psychoactive ingredient THC (tetrahydrocannabinol) dissolves in the far rich cell membranes and remains there. 50 per cent will still be there a week later and ten per cent after a month. Traces in the hair and urine will be detectable for weeks.

  2.2  Since THC is blocking the membranes, the orderly release of the many other neurotransmitters is disrupted. Not only does this impair the everyday functioning of the brain, but also the new connections, vital for the processes of learning and memory are not made. This is especially serious in adolescence, normally a time when a "growth spurt" of these connections occurs. Incidentally a joint today contains on average ten times as much THC as it did in the Sixties.

3.  The Immediate Effects

  3.1  It takes about 20 minutes for the effects of a smoked joint to peak, they last for two to three hours. Even with low doses, there is a huge downside to any feelings of euphoria. Thought processes fragment, there is an inability to sustain concentration, learning ability decreases and short-term memory deteriorates. This refutes the claim that cannabis actually helps study. Handwriting and motor co-ordination are consistently impaired.

4.  Long-Term Effects

  4.1  Since the late Eighties, Swedish and Australian researchers have used new and more sensitive techniques to investigate these. They found that sustained use of cannabis impairs the ability to carry out tasks requiring complex thinking, intellectual flexibility, forward planning and processing of information. There is consistent interference with short-term memory, an inability to cope with new situations or benefit from past experiences.

  4.2  Dr Nadia Solowij, an Australian researcher said in her book "Cannabis and Cognitive Function" (1998) "Use more often than twice per week for even a short period of time, or use for five years or more at the level of even once per month, may each lead to a compromised ability to function to their full mental capacity, and could possibly result in lasting impairments".

  4.3  No child using cannabis, even occasionally, will achieve his or her full potential—I know, I have seen it happen. It does not help that most of the messages youngsters receive, even from drug educators, dismiss cannabis as being "no big deal". We would raise educational standards at a stroke if we could only persuade our children to abstain.

  4.4  A former pupil who had been in trouble with cannabis at school said, "Tell them that they will become boring people. They won't want to go out, they'll sit watching TV and have no conversation". Most of his friends didn't make it to university. He scraped in. When he gradually realised that everything I had said about cannabis was true, he stopped, and is now doing research towards a PhD.

  4.5  Dr Solowij was not alone in hinting that damage to the brain may be permanent. In 1997 the WHO Report on Cannabis stated in its summary "The chronic use of cannabis produces additional health hazards . . . which may not recover with cessation of use, and which could affect daily life functions".

  4.6  Attempts to answer this question by experiments and brain scans have been inconclusive. But there are many things we accept without conclusive proof, such as the connection between smoking and lung cancer. Surely we should err on the right side of caution.

  4.7  Many clinical and anecdotal reports of long term impairment of mental functions exist especially from the developing countries. Permanent brain damage is a distinct possibility for cannabis users. It would be slow, subtle, insidious but cumulative. The risk is too great. Dead brain cells are never replaced and since they work in chains, if one cell dies, the whole message is lost.

5.  Personality Changes

  5.1  Cannabis users assume a different identity. They become passive, inflexible and rigid in thought. Since they never question their actions they're unable to change. They cannot take criticism and feel misunderstood. The negative feelings induced by the drug encourage more consumption and so the downward spiral continues. Trying to talk sense to users becomes a futile exercise.

  5.2  Youngsters have to forge an identity for themselves. They must eventually be able to fit into the adult world. New relationships have to be made and the world viewed in a realistic way. Cannabis use consigns them to a childish level of development, lacking independence and ill-equipped to make the transition.

  5.3  A long-running study of cannabis using children in 1988 found a higher level of psychosis and an undesirable social network in early adulthood. They were more likely to drop out of education, find it harder to hold down a job and were more likely to divorce.

  6.  With decriminalisation would come increased usage. More children would progress to hard drugs—they did in Holland. It does not bear thinking about.

September 2001

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Prepared 20 December 2001