I am writing in response to the letter entitled "Legalising 'pot'
a dangerous move". The writer claimed that cannabis is a gateway
drug - that it causes the use of harder drugs.

His (or her) friends are very unusual. British Home Office
figures show that around 24pc of 16-29 year olds in the UK have
tried cannabis. If, like his friends, these all went on to try
LSD, amphetamines and ecstasy, then the usage figures for these
drugs should be about the same. They aren't.

Amphetamine use is at 9pc, LSD 6pc, ecstasy 4pc and cocaine 3pc.
This means that more than 60pc of cannabis users never use
another illegal drug in their lives.

Just because cannabis use is sometimes followed by harder drug
use does not mean that cannabis caused the harder drug use -
alternatively, a single feature could cause both.
For example, day is followed by night. Day does not cause night,
both are caused by the mechanics of the Earth's rotation.
Similarly, both cannabis and harder drug use could be caused by a
daring thrill seeking personality.

Usage rates of cannabis, cocaine and LSD over the past twenty
years have all varied independently. The personality cause theory
fits this and other data better than the gateway theory.

So, although it may be true to say that 97pc of Heroin addicts
started with cannabis, this does not mean that cannabis caused
the heroin use, the cause is a personality trait present before
cannabis is first used. It is fair to say that 95% of Heroin
addicts were immunised by injecting as children. Does this mean
that injected vaccines are the first step on the road to
intravenous hard drug use?

If we are to accept the personality causes theory, then we can
conclude that if cannabis was more available and its use not so
discouraged, then the resulting increased use would not lead to
an increased use of harder drugs.

Paul Johnston
Knutsford, Cheshire