There is no scientific proof that cannabis use induces schizophrenia, Dutch scientists say, questioning recent research and an argument the Dutch government uses to crack down on marijuana-selling "coffee shops".
   
In an article in this week's Magazine for Psychiatry, a peer-reviewed journal, the three authors say that on the basis of currently available data "there is no justification for the proposed closure of coffee shops".
   
Often the first symptoms of schizophrenia occur during adolescence, when people start to experiment with drugs, but the scientists believe cannabis use only has a negative effect on people already genetically predisposed to the mental illness.
   
"It is therefore advisable that youngsters with a family history of schizophrenia and patients with a schizophrenic disorder be discouraged from using cannabis," the report said.
   
Subsequent Dutch governments have tightened rules on the sale of marijuana in government-regulated coffee shops, resulting in a significant reduction in the number of cannabis cafes.
   
A ban this year on alcohol in coffee shops will be followed by a ban on tobacco in 2005, outlawing all smoking on the premises.
   
There are around 780 coffee shops in the Netherlands of which 270 are in Amsterdam, according to 2002 figures.