Marijuana Use Speeds Onset of Schizophrenia, Study Says

Print More

For those at risk, marijuana use hastens the onset of schizophrenia, according to a new study.  Researchers found those with a genetic predisposition for psychosis would begin to experience symptoms an average of 2.7 years earlier if they smoked marijuana, and that can mean a greater disruption to their life.

“We’ve known for many years that people who develop schizophrenia earlier have a number of poorer outcomes,” Michael Compton, co-author of the report, told the magazine  Miller-McCune.

Schizophrenia typically begins between the ages of 18 and 28.  According to the researchers, developing symptoms earlier makes it harder for schizophrenics to succeed later in life because it impacts their ability to graduate high school or finish college.

Even though the disease is genetic 80 to 85 percent of the time, many at risk have no family members who suffer from schizophrenia.

“The risk is hidden,” Compton said. “We usually don’t know who is at risk until they have developed the disorder."

One thought on “Marijuana Use Speeds Onset of Schizophrenia, Study Says

  1. I would not dismiss out of hand the possibility that marijuana use may trigger an earlier onset of psychosis among individuals who develop schizophrenia.

    However, to be convinced, I would need to see some clear evidence that the average age of onset of symptoms has declined since marijuana use first became widespread in the late 1960s. Also, there should be clear evidence of earlier onset of symptoms in countries with high rates of marijuana use (the USA, Canada, etc.) than in countries with low usage (Sweden, Japan, etc.).

    Absent such evidence, there is no reason to take this claim seriously.

    —-Some other interesting studies related to this issue—-

    Increased cannabis use by the public has not been followed by a proportional rise in diagnoses of schizophrenia or psychosis, according to the findings of a study published September 2009 in the journal Schizophrenia Research.

    Investigators at the Keele University Medical School in Britain compared trends in marijuana use and incidences of schizophrenia in the United Kingdom from 1996 to 2005. Researchers reported that the “incidence and prevalence of schizophrenia and psychoses were either stable or declining” during this period, even though the use of cannabis among the general population was rising.

    “[T]he expected rise in diagnoses of schizophrenia and psychoses did not occur over a 10 year period,” authors concluded. “This study does not therefore support the specific causal link between cannabis use and incidence of psychotic disorders. … This concurs with other reports indicating that increases in population cannabis use have not been followed by increases in psychotic incidence.”

    http://www.ncbi.nlm.nih.gov/pubmed/19560900

    The results of a separate clinical trial, published in October 2009, reported that the recreational use of cannabis does not stimulate the production of dopamine in a manner that is consistent with the development of schizophrenia.

    http://www.ncbi.nlm.nih.gov/pubmed/19539765