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article imageDoes smoking marijuana cause schizophrenia?

By Yukio Strachan     Dec 10, 2013 in Health
Boston - Marijuana, the most commonly abused illegal drug used worldwide, has long been considered an environmental risk factor for developing schizophrenia. A new study from Harvard University tells a different story.
The National Institute of Mental Health (NIMH) describes schizophrenia as a chronic, severe, and disabling brain condition that affects 1.1 percent or 2.4 million American adults over the age of 18.
Psychosis (psyche = mind, osis = illness), a common symptom of schizophrenia, is defined as the experience of loss of contact with reality and usually involves hallucinations and delusions, NAMI states.
NIMH writes:
People with the disorder may hear voices other people don't hear. They may believe other people are reading their minds, controlling their thoughts, or plotting to harm them. This can terrify people with the illness and make them withdrawn or extremely agitated.
People with schizophrenia may not make sense when they talk. They may sit for hours without moving or talking. Sometimes people with schizophrenia seem perfectly fine until they talk about what they are really thinking.
Which came first?
Schizophrenia has been linked to a multitude of possible causes, including cannabis or marijuana use. That's because studies have shown that patients with schizophrenia use cannabis at higher rates than those of the general population. In fact, at the time of the first psychotic episode up to 40% of patients already use cannabis.
Many experts believed these findings were due to self-medication (those with schizophrenia finding relief of their symptoms through smoking marijuana).
But one study from 1987 and four more studies published in 2002 and 2003 told a different story. These studies found that those using cannabis were at increased risk of later suffering from schizophrenia. It was thought that schizophrenia somehow developed due to how cannabis effected the brain.
There's been controversy ever since.
Researchers at Harvard Medical School aimed to bring clarity to this issue.
Their study, "A controlled family study of cannabis users with and without psychosis," published online in the journal Schizophrenia Research on Dec. 4, presents an alternative explanation for the association between cannabis use and later schizophrenia: "having an increased familial morbid risk for schizophrenia may be the underlying basis for schizophrenia in cannabis users and not cannabis use by itself."
In other words, the possibility of developing schizophrenia depends on family history and not marijuana use itself.
To reach this conclusion, the study authors, led by Lynn DeLisi, MD, Professor of Psychiatry at Harvard Medical School, compared the family histories of 108 schizophrenia patients and 171 individuals without schizophrenia to determine whether cannabis use was a factor in developing the disorder, Canadian website Leaf Science reported.
The team divided the study participants into four groups:
Group 1:87 non-psychotic study participants with no drug use;
Group 2:84 non-psychotic study participants with cannabis use;
Group 3:32 patients with schizophrenia spectrum psychosis no drug use; Group 4:76 patients with schizophrenia spectrum psychosis with cannabis use.
"All cannabis using subjects used this drug during adolescence, and no other substance, with the exception of alcohol," the study authors wrote.
After analyzing the data, according to Leaf Science, the study authors concluded “that cannabis does not cause psychosis by itself. In genetically vulnerable individuals, while cannabis may modify the illness onset, severity and outcome, there is no evidence from this study that it can cause the psychosis.”
What's next?
Although DeLisi and her team conclude that cannabis is “unlikely” to cause schizophrenia, the study authors won't rule it out completely. The authors point out that different types of marijuana available may play a role in the outcome of schizophrenia, Leaf Science reported.
All in all: "An understanding of this link would have significant implications for legalization of cannabis and its medicinal value," the study authors wrote.
More about cannabis use and schizophrenia, marijuana use and schizophrenia, cannabis psychosis, morbid risk schizophrenia, Marijuana
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