The question of whether drug abuse increases the risk of developing schizophrenia and other mental illnesses has been a hotly debated topic for decades. New study from Denmark that includes data from more than 3 million individuals takes an in-depth look at the conundrum.
Cannabis creates a greater mental health risk than any other substance, including class A drugs, scientists have found.
Those who abuse the drug – now more potent than ever in the form of super-strength ‘skunk’ – are 5.2 times as likely to develop schizophrenia as someone who had never smoked it.
This compares to 1.9 times for hallucinogenic drugs and 1.24 times for amphetamines.
Danish researchers trawled more than 3.1million people’s medical records to ascertain the link between cannabis use and schizophrenia.
In study presented to the International Early Psychosis Association, they suggested the pleasure hormone dopamine, released by the drug, could trigger the disorder in people susceptible to its effects.
The mass medical records study looked at people diagnosed as being cannabis abusers by doctors and those who were schizophrenics.
It follows research last year which showed super-strength types of cannabis caused one in four cases of psychosis.
More than nine million people in England and Wales have smoked cannabis at some point. Pro-cannabis campaigners say the drug cannot be proven to have caused the psychotic disorder.
They claim people may be schizophrenics before they use cannabis and are more likely to take the drug in the early stages of illness to calm themselves.
But the Scientists at Copenhagen University Hospital’s Mental Health Centre also found evidence implying that cannabis made the brain schizophrenic.
In a second study they discovered that pregnant women who abused cannabis gave birth to children six times more likely to become schizophrenics. This suggests the physical effects of the drug could be passed on in the womb.
Study leader Dr Carsten Hjorthøj said: ‘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.’