The link between marijuana and schizophrenia or psychosis has been identified for a long time. Many research studies have shown that those who have used cannabis have a greater than average chance of having schizophrenia. What’s more, the more marijuana the person is exposed to, and the younger the exposure, the greater their risk of schizophrenia seems to be. Marijuana users may also develop schizophrenia, on average, two years sooner than non-users.
However, while this link is known, the causes of the link are not. Researchers aren’t sure if cannabis and schizophrenia are linked because the cannabis itself is increasing the risk of schizophrenia or because those with schizophrenia are predisposed to using cannabis (see Schizophrenia and Substance Abuse).
Marijuana and Psychosis
A major component of schizophrenia is psychosis, and it’s thought that marijuana may be able to induce or exacerbate psychosis. In fact, the latest version of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR) recognizes a form of psychotic disorder specifically induced by weed. Cannabis-induced psychotic disorder may occur with delusions or hallucinations just as the psychosis found in schizophrenia. 1
This also means that people with schizophrenia, who already experience psychosis, should stay away from weed as it may worsen their symptoms.
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Cannabis Use and Schizophrenia
In several studies, cannabis use and schizophrenia have been linked. Repeatedly, research has found that those who smoke cannabis are twice as likely to develop schizophrenia versus non-smokers. In addition, those with schizophrenia are more than twice as likely to smoke pot as opposed to those who are not schizophrenic.
There are many possible reasons for this connection. One is that schizophrenics may find marijuana more appealing than those without the disease. In fact, those with schizophrenia report feeling happier than those who use marijuana but are not schizophrenic. People with schizophrenia using cannabis also report a reduction in negative feelings, less anxiety and less social withdrawal. In spite of the fact that using marijuana may increase the hallucinations in this group, the positives are often seen to outweigh the negatives. Unfortunately, this leads to a high rate of addiction to marijuana for schizophrenics.2
Can Marijuana Cause Schizophrenia?
While many studies have been done looking at the use of weed and schizophrenia, a causal relationship cannot be established. Right now, the best guess of researchers is that for those with biological risk factors, using cannabis does, indeed, increase the risk of schizophrenia. For those with no pre-existing risk, marijuana may not increase their risk of developing schizophrenia. In short, more research is needed before an evidence-based understanding of the link between schizophrenia and marijuana is possible.3