Causal mechanism

Marijuana poses a greater mental health risk than any other substance, including class A drugs, according to new research out of Denmark.

Regular users of the herb, particularly its super-strength varieties, were found to be 5.2 times more likely to develop schizophrenia than non-users.

This compares to 1.9 times more likely in the case of hallucinogenic drugs and 1.24 times for amphetamines.

To ascertain the link between marijuana use and schizophrenia, the researchers combed the medical records of more than 3.1 million people.

The mass medical records search looked at people diagnosed as being marijuana abusers by doctors and those who were schizophrenics.

In a subsequent paper presented to the International Early Psychosis Association, the Danish scientists suggested that the pleasure hormone dopamine, which is released by the drug, could trigger the disorder in people susceptible to its effects.

The study followed research last year which indicated that super-strength types of marijuana caused one in four cases of psychosis.

Pro-marijuana campaigners maintain that the drug cannot be proved to cause schizophrenia, however.

They claim that people may be schizophrenics before they use marijuana and are likely to take the drug in the early stages of the illness as a calmative.

The researchers at Copenhagen University Hospital’s Mental Health Centre nevertheless found evidence implying that marijuana made the brain schizophrenic.

In a separate study, they discovered that pregnant women who abused marijuana gave birth to children six times more likely to become schizophrenics, suggesting that the physical effects of the drug could be passed on in the womb.

According to study leader Dr Carsten Hjorthøj: “We know a child in its mother’s womb is not doing this by choice. For me, that does set upon the idea that cannabis is a causal mechanism.

“We know schizophrenia is a disorder of the brain linked to dopamine and cannabis influences levels of dopamine.”