MAN, WE'VE GOT TO GET OUT OF THESE JOINTS

It Would Be Mind-Blowing Folly To Remain Silent While Cannabis Is Legalised

So how can we be sure that cannabis is harmless, and what is it that
is so good about it anyway? If you were to ask the same questions of
genetically modified foods, the answer would be: no evidence of harm
as yet, and much potential for good. Yet GM foods are reviled,
whereas for the drug that suddenly many want to legalise, the answers
are just the opposite.

We know that under experimental conditions exposure to cannabis can
cause a severe shrinkage and, indeed, death of brain cells - most
notably in key areas such as the hippocampus, related to memory.
Small surprise, then, that we see impairments in memory and thinking
with cannabis use.

But my own concern is more subtle and pervasive. We are born with
pretty much all the brain cells we will ever have - it is the
connections between cells that accounts for the growth of brain after
birth. Moreover, the most marvellous thing about being born a human
being is that you will enter the world with a unique configuration of
brain cell connections. So even if you are a clone - that is to say
an identical twin - you will have a unique brain.

As we develop more sophisticated brains, gradually emphasis shifts
from nature to nurture, from reliance on instinct and genetic
mandates to a flexibility where individual experiences can shape us
as individuals.

Examples abound of how the environment and our activities can
influence the connectivity of brain cells. For example, London taxi
drivers turned out recently to have a larger area of hippocampus than
other drivers of comparable age, and it has been shown that by
engaging in piano exercises people can enhance the brain territory
related to their fingers.

We know that experience and interaction with an enriched environment
can enhance the connections of the branches of brain cells, and that
will then dictate the degree of connectivity of which the brain is
capable. Hence, every moment of our lives we are "personalising" our
own individual brains. It is the result of this process that I would
call the "mind".

Of course, it is possible to "blow your mind" and be "out of your
mind". I would argue that that is precisely what one is doing with
drugs. Drugs work on the connections between brain cells, changing
the efficiency of how one cell communicates with another. Moreover,
by working at the chemical locks and keys that enable a transmitter
released from one brain cell to interact with the next cell along,
drugs can tamper with the message that is sent.

Viewed in this way, one can see that drugs have the potential to
leave a lasting mark on the brain. Drugs could, literally, transform
your mind.

Of course, an immediate answer is that cannabis is "no different"
from alcohol or nicotine. This claim is simply not true. Cannabis
spliffs are more pernicious than ordinary cigarettes - they contain
higher levels of carcinogens, tar and other toxins. And the primary
mechanism of the action of alcohol on the brain is quite different
from that of cannabis.

Alcohol works mainly on the walls of the brain cells, making them
more sluggish and less efficient at sending the electrical blips.
However, cannabis works on its very own receptors; this means that it
has a much more direct means for changing not just the short-term
signalling from one cell to another, but also a greater chance of
influencing long-term changes within the brain. The biochemical
potential is there, therefore, for cannabis to have a more targeted
and longer-lasting effect on brain functions.

I do not believe there has yet been a laboratory experiment comparing
directly and under identical conditions, in the same brain tissue,
the effect of alcohol versus nicotine. Nonetheless, we already know
that the effects of these drugs on human beings cannot be the same.

Not only are there reports of severe memory loss and other cognitive
impairments with cannabis, but there is the much vaunted pain-killing
effect. This effect of cannabis does deserve further exploration as a
therapeutic tool and, if it is proven, then it could well take its
place among prescribed drugs such as morphine. But there is a world
of difference between a drug prescribed under clinical supervision
for a recognised illness, for which any possible side-effects or risk
may be off-set by the misery of the condition, compared to taking a
drug in a healthy brain and body.

If cannabis is such a powerful pain-killer, then just think what it
does to the nervous system: it must be having, indeed, a very strong
effect. And since no one has recommended alcohol and nicotine with
equivalent enthusiasm for severe pain, surely that demonstrates that
analogies are fallacious.

It is impossible at this stage to make categorical statements as to
how dangerous cannabis is and how exactly it compares with other
drugs, but it is a drug and it is different from those that are in
legal use. Fine, if you wish to risk "blowing your mind"; changing
the way you see the world. But far from shrugging one's shoulders and
trying to turn the clock back to a Sixties hippy stance of passivity
and stupefaction, surely we should instead be questioning the
priorities of budgets, and how society operates.

Perhaps, most importantly, we should be asking why people want to
take cannabis in the first place.

We are not doing the public a service by pretending all is
pharmacologically cool man, nor by circumventing the issues of how to
make life really worth living in the 21st century.

Baroness Greenfield is a professor of pharmacology and Director of
the Royal Institution.