This article is taken from this webpage: http://www.thetimes.co.uk/article/0,,74-2001270168,00.html
I have not been changing anything in it, but repeated it in the form it was presented in the newspaper.
Cannabis:
why it is safe
BY COLIN BLAKEMORE AND LESLIE IVERSEN
Claims
by Baroness Greenfield and Dr Thomas Stuttaford that cannabis is harmful are an
idiosyncratic reading of the scientific and medical evidence. 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 animal based
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 (UK). 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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