Professor Susan GreenfieldIt is folly to legalise a drug that is known to leave users with permanent damage to their ability to reason, argues Susan Greenfield, the distinguished expert on brain processes (Sunday August 18 2002, The Observer) now that those anxious to look cool can puff cannabis freely in without fear of arrest, perhaps those of us who have argued that
relaxing the laws on cannabis is irresponsible and dangerous should
retreat gracefully behind our chintz curtains. Yet the downgrading of
the classification of cannabis perpetuates the same tired old myths
and the same serious problems.

Take the myth that cannabis is ‘just the same as’ alcohol. A glib yet logical riposte might be that if the drugs are truly identical why not just stick with the booze? What is the distinct appeal of cannabis that can be ignored in equating the two drugs? Such sophistry is inappropriate because alcohol and cannabis work on the brain and body in very different ways. Alcohol has a range of non-specific actions that affect the tiny electrical signals between one brain cell and another; cannabis has its own specialised chemical targets, so far less has a more potent effect.
Moreover, although drinking in excess can lead to terrible
consequences, there are guidelines for the amount of alcohol that
constitutes a ‘safe’ intake. Such a calculation is possible because we
know alcohol is eliminated relatively quickly from the body.

With cannabis, it is a different story. The drug will accumulate in
your body for days, if not weeks, so, as you roll your next spliff,
you never know how much is already working away inside you. I
challenge any advocate of cannabis to state what a ‘safe’ dose is.
Until they do, surely it is irresponsible to send out positive
signals, however muted? Another notion is that cannabis is less
harmful than cigarettes. I’m not sure how this idea came about,
certainly not as the results of any scientific papers. We do know
cannabis smoke contains the same constituents as that of tobacco:
however, it is now thought that three to four cannabis cigarettes a
day are equivalent to 20 or more tobacco cigarettes, regarding damage
to the lining of the bronchus, while the concentration of carcinogens
in cannabis smoke is actually higher than in cigarettes. And if
cannabis were ‘just the same’ as alcohol and cigarettes, why are
people not taking those already legal drugs for the much-lauded
pain-relief effects? After all, another case for the relaxation of the
laws on cannabis is the ‘medical’ one that it is an effective
analgesic. But there is a world of difference between medication
prescribed in a hospital, where the cost-benefit balance tips in
favour of pain relief, compared to a healthy person endangering their
brain and body needlessly. Even the most loony of liberals has not
suggested tolerance for morphine or heroin abuse, because they
are prescribed clinically as potent painkillers. And think about it:
if cannabis brings effective relief from pain, then how does it do so?
Clearly by a large-scale action on the central nervous system.
Further wishful thinking is that, because cannabis doesn’t
actually kill you, it is OK to send out less negative legal signals,
even though the Home Secretary admits that the drug is dangerous.
Leaving aside the issue that cannabis could indeed be lethal, in that
the impaired driving it can trigger could well kill, there is more to
life than death. It is widely accepted that there is a link between
cannabis and schizophrenia: as many as 50 per cent of young people
attending psychiatric clinics may be regular or occasional cannabis
users. The drug can also precipitate psychotic attacks, even in those
with no previous psychiatric history. Moreover, there appears to be a
severe impairment in attention span and cognitive performance in
regular cannabis users, even after the habit has been relinquished.
All these observations testify to a strong, long-lasting action on the
brain. Some attempts have been made in laboratories to work out
what cannabis could actually be doing to brain cells. So far,
some data have suggested that there can be damage to neurons, and at doses comparable to those taken on the street.

None the less, others argue that the experimental scenario of isolated neurons growing in a lab dish are hardly a natural situation, and that such data have to be interpreted with caution. But absence of evidence is not evidence of absence. The effects on the brain in real life are most probably
subtle and therefore hard to monitor: it’s not so much that cannabis
will create great holes in your brain, or deplete you wholesale of all
your best neurons. Instead, by acting on its own special little
chemical targets (and because it will therefore work as an impostor to
a naturally occurring transmitter), the drug is likely to modify the
configuration of the networks of brain cell connections. These
configurations of connections make you the unique person you are, since they usually reflect your particular experiences. So a change
will be hard to register from one person to another, and certainly
from one slice of rat brain to another: but still, it will make you
see the world in a different way – characteristically one depleted of
motivation.

It is hard for me, as a neuroscientist, to accept that a
drug that has the biochemical actions that it does, that hangs
around in the brain and body, and that has dramatic effects on brain
function and dysfunction, could not be leaving its mark, literally, on
how our neurons are wired up and work together. It is argued that
we will never stamp out cannabis use, and therefore we should
give up trying. But we will not stamp out murder or house break-ins or mugging, yet I’ve never heard an argument for freeing up police time
by liberalising the law on these acts. Laws, it is said, are
only enforceable when the majority wants them enforced, yet the
arguments used for easing up on cannabis apply equally to promoting
ecstasy or other mind-bending substances.
Do we really want a drug-culture lifestyle in the UK? Cynically, one could argue that it is politically expedient to court the youth vote, to open up the
inevitable prospect of revenue from a new source of taxes and to help
the ailing tobacco industry prosper from a great new product of
readymade packets of spliffs. The condoning of chemical consolation
also distracts from other problems. We have failed our young
people in providing homes and jobs and, by giving them an easy route into a chilled-out oblivion, have turned our backs on the far more challenging prospect of initiating policies to help them realise their
potential and live better and more fulfilling lives. They are paying a
high price for cool.

Source: www.guardian.co.uk/science Aug.2002