Understanding science

7: Drugs of Addiction: Biological, Medical, Legal and Ethical Aspects

Is cannabis a special case?

After alcohol and tobacco, cannabis is the third most widely consumed psychoactive drug in the Western world. More than one third of 18 year olds admit having tried cannabis at least once, and some 5% of 16-49 year olds are regular users (more than once a month). In the UK between 1-2 million people choose to ignore official advice about the dangers of cannabis and are willing to risk breaking the law. Illegally imported cannabis resin is readily available, and the street price of around £5 per gram means that it is cheaper to smoke cannabis than tobacco.

There have been many studies of the health hazards of cannabis and the results overall suggest that these have been exaggerated. Claims in the 1970s that regular cannabis use could lead to reduced immune responses and damage to reproductive function, including foetal abnormalities, have not been substantiated. The acute toxicity of the active ingredient in cannabis - delta-9-tetrahydrocannabinal - is very low. There are virtually no recorded cases of death due to overdose. Unlike alcohol, cannabis intoxication is not associated with heightened aggression and violence. Some regular cannabis users become psychologically dependent on the drug. But unlike cigarette smokers, who need tobacco every day and often form a lifelong habit, cannabis users often use the drug only a few times each month and the majority quit before they reach the age of 30.

Nevertheless, cannabis use is not risk-free. Smoking cannabis is potentially as dangerous to health as smoking tobacco, and in the UK this is made worse as cannabis and tobacco are often smoked together. It took fifty years to establish the link between tobacco smoking and cancer and cannabis has only been in common use for 25 years. There is a possible "time bomb" here awaiting the younger generation of cannabis users. Acute intoxication with cannabis, especially when combined with alcohol, is certainly a hazard to drivers, and makes the user incapable of any intellectually demanding work. As many as one third of regular users may become dependent on the drug, sometimes to the extent that it will come to dominate their lives. For those suffering from psychotic illness, cannabis use is likely to make them worse.

Where does this leave us in terms of drug policy? While several countries in Europe and Canada are proposing a relaxation of the criminal penalties for recreational cannabis use, the UK government refused to consider even the modest reduction in criminal penalties proposed by the Police Foundation in their 2000 report "Drugs and the Law". In practice half of all those arrested for cannabis offences are let off with a police caution, but this is open to criticism of "postcode prosecution", as the proportion cautioned ranges from 60% in London to 13% in Durham (Home Office Statistics, 1998). In future will we edge towards a "grudging acceptance" of cannabis as part of our culture?

L Iversen "The Science of Marijuana", 2000, Oxford University Press.

Police Foundation Report "Drugs and the Law", Report of the Independent Inquiry into the Misuse of Drugs Act 1971.

Prof Les Iversen is Visiting Professor of Pharmacology, University of Oxford

The title of this document is: Understanding science: 7: Drugs of Addiction: Biological, Medical, Legal and Ethical Aspects
URL: http://www.cam.ac.uk/about/scienceseminars/drugs/cannabis.html

Seminar presented: 02/10/2001