An increasing number of international studies show that smoking cannabis can induce both schizophrenia, psychosis and depression in adolescents, according to psychiatrist Merete Toft, a consultant at Bispebjerg Hospital. Toft said that studies in Sweden, New Zealand and the Netherlands had concluded that the earlier young people start using cannabis and the more they smoke, the greater they risk becoming mentally-ill.
"Studies show that cannabis can induce psychosis and schizophrenia in people who would not have been sick if they had not smoked it," Toft told Kristeligt Dagblad newspaper. She rejected the widespread explanation that the high correlation between cannabis use and mental illness occurs when people who are already ill use the drug to numb their symptoms.
"Even when adjusted for anything that suggests self-medication, the figures show that eight to ten percent of all schizophrenics have become ill because they have smoked cannabis," said Toft. "That adds up to as many as 1,500 of the schizophrenics in Denmark, and that it is a very serious problem."
Other studies have shown that the risk of developing depression increases with extended cannabis use. Toft believe that the risk is twice as high for young people who use cannabis as opposed to their abstinent peers. Other researchers put the risk at four times as high.
"Cannabis has a safe reputation, but it is not harmless," said Toft. She would like to see increased public information and would like politicians to drop the idea of legalising it.
Alice Thorup, the head of the prevention department at the northern Jutland Abuse Centre, said that the push for legalisation promotes the idea that cannabis is harmless.
"Young people are a product of adult society," Thorup told Kristeligt Dagblad. "They are affected when it seems like adults accept cannabis as an okay drug."
Four out of ten boys and three out of ten girls between 16 and 20 have tried cannabis, according to figures from the health department, making it the most commonly used drug in Denmark after alcohol.