Using marijuana, or cannabis, may cause psychosis to develop sooner in patients already predisposed to developing it, and in other patients the drug may even cause psychosis, according to a new study published in the Archives of General Psychiatry.

"This finding is an important breakthrough in our understanding of the relationship between cannabis use and psychosis," according to the study. "It raises the question of whether those substance users would still have gone on to develop psychosis a few years later."

Patients with psychosis tend to lose touch with reality and are prone to hallucinations and delusions about what is happening around them. Psychosis is frequently reported among patients with diagnosed mental illness such as schizophrenia and bipolar disorder.

What is schizophrenia?

According to the study led by Australian researchers, in which data from 83 studies involving more than 20,000 patients were analyzed, marijuana users experienced psychosis about three years younger than non-users. Users of other substances (besides pot) experienced symptoms of psychosis two years sooner. Alcohol use had no influence on development of psychosis, according to the study.

"Reducing the use of cannabis could be one of the few ways of altering the outcome of the illness because earlier onset of schizophrenia is associated with a worse prognosis," according to the study. "An extra two or three years of psychosis-free functioning could allow many patients to achieve the important developmental milestones of late adolescence and early adulthood that could lower the long-term disability arising from psychotic disorders."

But experts say the complexity of interaction between genes and environment, and the possibility that cannabis is, in fact, a way to self-medicate when psychotic symptoms arise are not accounted for in this study.

The marijuana-schizophrenia link

"It is distinctly possible, in fact likely, that folks who experience initial symptoms turn to cannabis in an effort to control them, then end up having a psychotic break of some sort earlier simply because they had their first symptoms earlier," said Mitch Earleywine, an associate professor of psychology at the State University of New York at Albany, who is also a marijuana policy expert. "This predicament makes it look as if cannabis preceded the psychotic symptoms when, in fact...folks with worse symptoms who are more likely to have an early break might simply be more likely to turn to cannabis."

Theories about an association between marijuana use and schizophrenia include several –sometimes interrelated - scenarios: The possibility that cannabis causes schizophrenia; that cannabis may cause people vulnerable to schizophrenia to develop symptoms; that cannabis may make schizophrenia symptoms worse; or that people with schizophrenia are more likely to use cannabis, according to the study.

Study authors suggest that this study, "lends weight to the view that cannabis use precipitates schizophrenia and other psychotic disorders," perhaps because of some confluence of genetic and environmental factors, or because using cannabis early in life may disrupt brain development.

"[This study] found that cannabis is associated with early onset of psychosis and that is most likely true but it doesn't answer the question of which way it goes," said Dr. Charles L. Raison, associate professor in the department of psychiatry at Emory University, and CNNHealth's mental health expert doctor. "Does smoking cannabis early in life make you vulnerable to getting early psychosis or is the first manifestation of psychosis to do drugs and alcohol, or is it both?"

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Raison added that other studies suggesting a causal relationship between marijuana use and psychosis disagree with this one.

Whatever the relationship between cannabis and psychosis, experts can agree that early use of cannabis is problematic.

"No one wants to see young people get heavily involved with any psychoactive substances," said Earleywine.