CANNABIS, WHY IT IS SAFE

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
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.