The link between cannabis and schizophrenia confirmed

The link between cannabis and schizophrenia which was put forward in 1987 is confirmed by the results of new studies says Jeanne Etiemble, Director at Inserm collective expertise.

A pioneering study published in 1987 and performed in Swedish conscripts during the period 1969-1970, showed an increased risk of developing schizophrenia in people who had used cannabis at the age of 18 and without psychiatric disorder, compared with people who have never used this product.

But no indication was given on the possible prior existence of latent psychiatric disorders among these people with schizophrenia. Remained the central issue of whether cannabis is likely to cause, by itself, as a psychiatric illness, said the scientist.

The collective expertise on "cannabis, what effects on the behavior and health?" published in November 2001 and has remained on this question.

Three new studies published in 2002 confirm the role of cannabis in the onset of schizophrenia. "The findings go in the same direction," she said.

The group of Swedish conscripts study has been extended to 50,000 people and various factors were taken into account. The researchers found "a significant excess of schizophrenia." In another study of 4,000 non-psychotic Dutch, the risk of onset of schizophrenic symptoms is more important "in patients using cannabis with a relationship between the dose consumed and the presence of symptoms." More people have severe symptoms, the greater the influence of cannabis is important.

A study of 700 New Zealand leads to similar results. Those who consumed at least three times cannabis at the age of 15 or 18 have a four times greater risk of presenting symptoms of schizophrenia at the age of 26 years compared to those who have never used the product more one or two times.

Moreover, it appears through various studies that the risk increases when consumption begins at the age of 15 years compared to the age of 18.

All persons with cannabis will not become schizophrenic, but the use of the product appears as one of many factors of the disease (with increased risks ranging from 2 to 6), alongside such genetic factors recently highlighted by a French team.

THE THEORY OF CLIMBING LITTLE EVIDENCE

This reassessment of risk is an element of updating the collective expertise of INSERM which also took into account the new data-less evidence on the controversial theory of "escalation".

According to this theory, the use of cannabis may cause an increased risk of subsequent use of other drugs including heroin risk.

However, to date, no data shows an explosion of heroin while the cannabis growing, especially among boys aged 16-17: a teen couple has tried cannabis in 2003 against one in five 1993.

Similarly, the use of animal models do not support the hypothesis of a causal link between cannabis use and the onset of opiate dependence (heroin), said Jeanne Etiemble. However cannabinoids are able to induce a relapse of self-administration behavior (addiction) of psychostimulants (amphetamines), opioids (morphine) and ethanol in previously dependent animals.

Finally, the implication of cannabis in the occurrence of coronary and cerebral vascular accidents is not currently established by epidemiological studies, but only discussed through case studies of growing since 2001, said Jeanne Etiemble.