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Cannabis Campaigners' Guide News Database result:
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UK: Cannabis: why it is safe
Colin Blakemore and Leslie Iversen The Times
Monday 06 Aug 2001 Public opinion on cannabis is shifting. The question of whether the law on cannabis (and other drugs, too) should be liberalised is, of course, complex and politically charged. Some of the arguments are legal, some ethical, but the decision should also be based on accepted scientific opinion. So it was disappointing that Baroness Greenfield of Ot Moor and Dr Thomas Stuttaford, both influential communicators of science and medicine, have recently condemned cannabis as a seriously harmful drug. In alarmist articles in The Times and elsewhere, they argued that scientific evidence shows that cannabis is addictive, causes personality change and psychosis, promotes heart disease and cancer, is more harmful than alcohol, and impairs driving long after intoxication has worn off. Most disturbing of all, Lady Greenfield claimed that even a single cannabis joint shrinks and kills brain cells and scrambles nerve connections. Certainly, if this represented the prevailing scientific view, and especially if cannabis were thought to be more dangerous than alcohol and tobacco, it would undermine any argument for relaxation of the law. But theirs is an idiosyncratic interpretation of the scientific and medical evidence. Of course, all drugs are harmful if taken in excess - even aspirin kills many elderly people every year because of its tendency to cause gastric bleeds. But in judging the risks of cannabis, we need to keep a sense of proportion and listen to the consensus reached by several recent exhaustive reviews of this topic from medical and scientific experts on both sides of the Atlantic. These include the British Medical Association, the Police Foundation, the US Institute of Medicine, and the House of Lords Science and Technology Committee. Although it cannot be assumed that cannabis use is entirely harmless, many of the points stated as established facts do not seem persuasive. In our opinion, the views of Lady Greenfield and Dr Stuttaford do not reflect the current balance of scientific and medical opinion, and it is questionable whether they would have passed the rigorous process of peer review and editorial control that regulate professional communications between scientists. It is claimed that cannabis smoke is more harmful to the lungs than tobacco smoke because it contains much the same mixture of noxious substances, and because cannabis users inhale more deeply and deposit more tar in their lungs. On the other hand, cannabis users do not smoke 20 to 40 times a day, as many cigarette smokers do. There may be a health risk, and it is compounded by the combination of cannabis with tobacco, but there is currently no indisputable evidence for a link with cancer. The reports of cancers of the throat, mouth and larynx in cannabis users were based on small numbers and did not rule out effects of the concomitant use of tobacco. A much larger study in the United States monitored the health of a group of 65,000 men and women over a ten-year period. The 27,000 who admitted to having used cannabis showed no association between cannabis use and cancers, nor were there any other serious adverse effects on health. It is implied that cannabis is inherently more harmful than alcohol. This contradicts received opinion. Unlike cannabis, alcohol in overdose can kill. Chronic alcohol abuse has well-documented health risks, including liver disease and severe brain damage leading to a form of dementia. Use by pregnant women also carries the risk of damage to the foetus, leading to severe mental impairments. There is no firm evidence that cannabis use carries any of these serious health risks. Several expert groups that have compared the risks of alcohol and cannabis have concluded that cannabis is less dangerous. As the Police Foundation's report last year stated: 'When cannabis is systematically compared with other drugs against the main criteria of harm (mortality, morbidity, toxicity, addictiveness and relationship with crime), it is less harmful to the individual and society than any of the other major illicit drugs or than alcohol and tobacco'. Cannabis produces a variety of well-documented short-term effects on perception, memory, thought and coordination, which might be expected to compromise driving skills. Lady Greenfield suggests that it does so for more than 24 hours after smoking, but the evidence for this is far from clear-cut. There are many serious studies that show little or no effect on driving even during acute intoxication. The association of cannabis with traffic accidents and deaths is hard to interpret, as most of these also involve alcohol. And, just as for alcohol and mobile telephones, evidence for an effect on driving would not argue for an outright ban. Lady Greenfield asserts that even tiny doses of cannabis cause brain damage. In correspondence with us she has cited recent research on nerve cells maintained in test-tube conditions, but the lowest concentration of the drug that caused any effect was still many times higher than that likely to be found in blood after cannabis use. It is generally accepted that observations in living animals and people carry greater weight in risk assessment than experiments on isolated cells. A wealth of such data has failed to show evidence of organic brain damage either in chronic human cannabis users or in animals treated with very high doses of cannabis extract or its active ingredient. In these studies doses up to 1,000 times higher than those needed to produce intoxication in man were given to rats or monkeys every day for 90 days, without causing serious adverse effects on the brain or other organs . Dr Stuttaford says cannabis is so harmful that it would not pass animalbased toxicity testing. But it already has! The benign results of those tests have allowed the active ingredient of cannabis, tetrahydrocannabinol (THC), to be registered as a prescription medicine in the US. The data also satisfied Britain's Medicines Control Agency. In contrast to the title of Dr Stuttaford's article 'Cannabis Kills', the British Medical Association, in its 1997 report, Therapeutic Uses of Cannabis, concluded that 'the acute toxicity of cannabinoids is extremely low: they are very safe drugs and no deaths have been directly attributed to their recreational or therapeutic use'. For some users, perhaps as many as 10 per cent, cannabis leads to psychological dependence, but there is scant evidence that it carries a risk of true addiction. Unlike cigarette smokers, most users do not take the drug on a daily basis, and usually abandon it in their twenties or thirties. Unlike for nicotine, alcohol and hard drugs, there is no clearly defined 'withdrawal syndrome' - the hallmark of true addiction - when use is stopped. And while some heavy users of cannabis become demotivated and unfit for intellectually demanding work, several studies of regular users have shown remarkably little impairment in academic grades or work output. The claim that cannabis use can lead to psychosis is a longstanding one. There was a lively debate in the British Medical Journal in 1893, for example, as to whether the endemic use of hashish in Egypt led to mania and insanity. There was also concern that the mental asylums in British-controlled India were filling with cannabis-induced lunatics. In 1894, the Indian Hemp Drugs Commission, after questioning more than 1,100 witnesses, concluded that there was no such causal link; this has been the position reached by most subsequent studies. It is accepted that cannabis can exacerbate existing mental illness and may itself cause a temporary toxic psychosis if taken in overdose. But there is no evidence that the actual incidence of the true psychoses - schizophrenia, bipolar disorder and depression - has risen over the past 50 years, while the number of users has risen from virtually zero to more than half the young population. Dr Stuttaford claims that cannabis damages the heart and cardiovascular system, and may impair sexual development and function. Even small doses of cannabis do have effects on the heart and circulation, but regular users tend to become tolerant of these effects, and it is not generally accepted that cannabis use leads to increased incidence of cardiovascular illness. The suggestion that cannabis may adversely affect reproductive function is based largely on animal experiments that used very high doses. There is no evidence that cannabis use adversely affects human fertility. Finally, the portrayal of the Dutch experiment in decriminalising cannabis as a disaster is at odds with much careful analysis performed by Dutch and other experts. It is true that heroin use has risen in The Netherlands since cannabis decriminalisation, but it has risen more here. Significantly, the use of hard drugs has declined in recent years in The Netherlands, while it is still rising in the UK and most other Western countries. The Netherlands has fewer drug-related deaths than any other European country and cannabis consumption is somewhat lower there than here. Significantly, it is substantially lower among schoolchildren - the very group that everyone most seeks to protect. More than half of Britain's young people have used cannabis. We think that it is wrong to wish on them a criminal record that could blight their lives, and we hope that the cannabis debate will not be stifled by fears that it is a deadly drug. Leslie Iversen, FRS, is Visiting Professor of Pharmacology at Oxford University and the author of The Science of Marijuana (Oxford University Press, 2000). He was a specialist adviser to the House of Lords Select Committee on Science and Technology for its review of the medical uses of cannabis. Colin Blakemore, FRS, is Professor of Physiology at Oxford University, Director of the Oxford Centre for Cognitive Neuroscience and president of the Physiological Society. He is a former president of the British Association for the Advancement of Science.
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