Schizophrenia could make people use cannabis, not the other way round

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Schizophrenia and cannabis genetic link: Disorder may drive people to smoke pot, DNA study finds

Schizophrenia and cannabis are genetically linked: Mental disorder may drive people to smoke pot, DNA study finds

  • Scientists have discovered 35 ‘overlapping’ genes linking the two traits
  • Cannabis may not cause schizophrenia – the illness could lead to the drug use
  • Marijuana users are also more likely to be outgoing or take risks, the study said
  • But experts have not ruled out cannabis contributing to the illness 

People at high risk of schizophrenia are more likely to smoke cannabis, a study has found.

Scientists studied more than 180,000 people worldwide using data from DNA testing website 23andMe as well as UK health records and past studies.

They found 35 genes which influence whether people are ever likely to smoke marijuana.

And the same genes also affect how likely someone is to develop schizophrenia, showing that as the likelihood of one increases, the other does, too.

The illness could actually be driving people to use cannabis in order to cope, the researchers suggest, instead of the previously-held belief that the drug can directly cause the condition.

And similar genetic links mean people are also more likely to have extroverted personalities or indulge in risky behaviour – which could drive them to smoke pot.

But the study does not give any evidence to prove that smoking marijuana does not contribute to mental health problems.

People who are genetically more likely to get schizophrenia are also more likely to use cannabis, but the drug may not directly cause the condition, according to international research

The study was carried out by researchers at the QIMR Berghofer Institute in Brisbane, Radboud University in the Netherlands and Virginia Commonwealth University in the US. 

Researchers used data from past scientific studies and medical records, as well as from the website 23andMe, which offers private DNA and ancestry testing by post.

They found what they called a ‘genetic overlap’ in people’s DNA.

The overlap revealed there are some genes which increase both someone’s chance of developing schizophrenia and their tendency to smoke cannabis.


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In the study the authors say the genes make people more likely to smoke cannabis by making them more likely to take risks or behave impulsively – traits they say are associated with people who use marijuana.

‘That is not a big surprise because previous studies have often shown that cannabis use and schizophrenia are associated with each other,’ said Jacqueline Vink of Radboud University.

People vulnerable to schizophrenia are more likely to use cannabis 

‘Our study showed that people with a vulnerability to develop schizophrenia are at increased risk of using cannabis.’ 

Many of the 35 overlapping genes also appear to make it more likely that someone will smoke cigarettes or drink alcohol.

Past research suggested drug triggered the illness 

Past research has suggested that smoking cannabis can trigger schizophrenia or other mental illnesses.

But this study shows marijuana use may not be a direct cause but people could instead be using cannabis to cope with the illness, or the drug could contribute to an already-existing condition.

Professor Eske Derks from Queensland’s QIMR Berghofer Institute said: ‘This may suggest that people with schizophrenia use cannabis to cope with the symptoms.

‘These findings don’t rule out the possibility that cannabis use could also contribute to the onset of schizophrenia; however, we haven’t found any evidence to support that in this study.’

The study was published in the journal Nature Neuroscience.

DOES CANNABIS INCREASE THE RISK OF PSYCHOSIS? 

Going from being an occasional marijuana user to indulging every day increases the risk of psychosis by up to 159 percent, research revealed in July 2017.

Marijuana is thought to cause psychosis-like experiences by increasing a user’s risk of depression, a study found. The two mental health conditions have previously been linked.

Frequently abusing the substance also significantly reduces a user’s ability to resist socially unacceptable behavior when provoked, the research adds.

Study author Josiane Bourque from the University of Montreal, said: ‘Our findings confirm that becoming a more regular marijuana user during adolescence is, indeed, associated with a risk of psychotic symptoms. 

‘[Psychosis symptoms] may be infrequent and thus not problematic for the adolescent, when these experiences are reported continuously, year after year, then there’s an increased risk of a first psychotic episode or another psychiatric condition.’ 

The researchers, from the University of Montreal, analyzed around 4,000 13-year-olds from 31 high schools in the surrounding area.

Every year for four years, the study’s participants completed questionnaires about any substance abuse and psychotic experiences.

Psychotic symptoms included perceptual aberration – for example feeling that something external is part of their body – and thinking they have been unjustly badly treated.

The participants also completed cognitive tasks that allowed the researchers to assess their IQ, memory and stimuli response.

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