CANNABIS: A BURNING ISSUE

Over the past few years, our knowledge of the adverse impact of
cannabis on mental health has increased substantially (A little light
confusion over cannabis drug date, January 22). There is now
considerable clinical evidence linking cannabis use to mental illness,
especially schizophrenia, psychosis, anxiety and depression.

A person, who uses cannabis by age 15 has more than a four-fold
increased risk of developing schizophrenia symptoms over the next 11
years compared to a person starting to use cannabis by age 18.
Eighteen-year-olds who have used cannabis 50 times have a nearly
seven-fold increased risk of developing psychosis over the next 15
years.

Up to 80% of new cases of psychosis currently seen in some psychiatric
hospitals are triggered by cannabis abuse. Psychiatric services,
especially in London, are near crisis point. Over the past three
decades, a doubling of the prevalence of schizophrenia has been
observed in London. While it is too early to say whether this is due
to the increase in cannabis abuse over the past decades, this
possibility cannot be discounted on current evidence.

In addition, cannabis has significant negative effects on intellectual
functioning, including learning, concentration and educational
achievement. Three to four cannabis cigarettes are as damaging to the
airways as 20 nicotine cigarettes a day. Severe lung damage due to
bronchitis and emphysema and also head and neck cancers have been
observed in young cannabis users.

We are concerned that the imminent reclassification of cannabis will
send out the message that cannabis is harmless and legal, increasing
cannabis abuse with all the adverse effects on an already
overstretched NHS.

Dr Clare Gerada Director of drugs training programme, Royal College of
General Practitioners

Prof Heather Ashton School of neuroscience, University of
Newcastle

Hamish Turner
Coroners Society

Dr Hans-Christian Raabe
GP, The Family Practice