IS CANNABIS more鈥攐r less鈥攈armful than its legalised cousins
alcohol and nicotine? Last week, bang on cue, this hoary old question surfaced
yet again as the British government signalled its intent to relax the laws on
cannabis possession, and join what is becoming an almost global trend.
Other countries have already taken steps towards decriminalising possession,
but nobody expected the same from Britain
(see 鈥淕oing to pot?鈥�).
The admission that cannabis is not as harmful as heroin and cocaine goes
against everything it鈥檚 been saying for years. It also leaves the US, which is
sticking to this hardline position, increasingly isolated.
But not quite alone. One of the strongest attacks on Britain鈥檚 U-turn came
from the nation鈥檚 best-known neuroscientist, Susan Greenfield鈥擮xford
pharmacologist, TV presenter and now a member of the House of Lords. In a
thundering broadside in a daily paper, Greenfield blasted liberal campaigners
who seek to play down the evidence that cannabis permanently damages the brain.
It鈥檚 good to see scientists of Greenfield鈥檚 standing voicing strong opinions on
public issues. However, having reported on the science of cannabis for many
years, we have to disagree with her conclusions.
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To take just one example, she points out that some 7000 milligrams of alcohol
are needed to achieve intoxication, whereas for cannabis the figure is just 0.3
milligrams: cannabis is far more potent and hence far more dangerous, she
reasons. But what this really means is that you have to have 20,000 times as
much alcohol coursing through your veins before you feel the effects. By then
your liver is having to work overtime. Alcohol certainly lacks cannabis鈥檚
ability to act on brain receptors in a potent and specific manner: that is one
reason why booze can be so deadly.
A number of cannabis users do develop a serious dependency problem. And in
excess the drug can lead to poor concentration, even bouts of paranoia. But
permanent brain damage? A few lab studies have, it鈥檚 true, reported that
cannabis-like substances can harm nerve cells cultured in the test tube. But
such cultures are notoriously fragile, and other studies have found no signs of
brain damage in animals given doses far higher than those needed to produce
intoxication in humans.
And even if they hadn鈥檛, it wouldn鈥檛 matter鈥攁t least not as far as
changing the laws on cannabis go. The evidence from other countries is that more
relaxed laws do not lead to more youngsters using the drug. Wherever cannabis
lies in the league table of harmful substances, there seems little point in
imprisoning people for possessing small amounts unless this is likely to make
the drug less popular. And all the signs are that it doesn鈥檛.
