recent editorial for the Journal of Psychiatry & Neuroscience, Matthew Hill, PhD of the University of Calgary’s Hotchkiss Brain Institute addressed the scientific evidence behind the debate.
Here are 4 main facts about marijuana and schizophrenia that Dr. Hill highlights.
1. Marijuana does not cause schizophrenia.
While scientists are still studying the link between marijuana and schizophrenia, it is abundantly clear at this point that marijuana use alone does not cause one to develop schizophrenia.
The most convincing line of evidence, Dr. Hill notes, comes from epidemiological data:
“Within the Western world, cannabis use went from essentially nonexistent in the 1950s to extremely prevalent in the 1960s and 1970s. Despite this dramatic shift in cannabis use at a societal level, the prevalence of schizophrenia has largely remained stable.”
Marijuana, however, can cause psychosis-like symptoms, such as paranoia, and at very high doses, auditory or visual hallucinations. But these are just temporary and are not considered signs of mental illness.
2. Marijuana may help treat schizophrenia.
Most of the studies linking marijuana to higher rates of schizophrenia can be explained by the opposite relationship. That is, individuals with schizophrenia may be more likely to use cannabis because it helps them in some way or another.
Likewise, there is evidence that supports marijuana as a treatment for schizophrenia. For example, studies have linked marijuana use to better cognitive performance among schizophrenics. Also, a 2012 clinical trial involving 39 schizophrenia patients compared cannabidiol (CBD), a compound found in marijuana, with a commonly prescribed antipsychotic, amisulpride, and found treatment with cannabidiol resulted in superior outcomes.
3. Marijuana may increase the risk of schizophrenia in vulnerable individuals.
Somewhat contrary to marijuana’s ability to help treat schizophrenia is evidence that it may provoke the onset of psychotic episodes in individuals with a vulnerability to schizophrenia.
But the strength of this evidence is moderate at best. Some studies have linked marijuana use to physical abnormalities of the brain, while others have not. Also, studies suggest marijuana can alter dopamine release, which is known to contribute to psychosis, but alcohol, tobacco and all other substances of abuse do the same.
Ultimately, while the potential for marijuana to exacerbate the risk of schizophrenia is a logical suggestion, scientists are still searching for concrete evidence that supports the notion.
4. Extreme opinions are unscientific.
In recent years, the link between marijuana and schizophrenia has become a focal point in the debate surrounding legalization of recreational use. As Dr. Hill notes:
“While many conditions, including lung cancer and cardiac arrthymias, have been at the forefront of the cannabis safety debate for some time, interestingly the discussion has predominantly moved to psychiatry – specifically the association between adolescent cannabis use and the development of schizophrenia.”
But Dr. Hill adds that “the extreme opinions on the subject are not rooted in science.”
At this point, it is impossible for anyone to accurately claim that marijuana is a cause for schizophrenia, or that the risk of schizophrenia is a valid reason to keep marijuana illegal.
For example, even assuming cannabis does cause schizophrenia, a study published in 2009 concluded that preventing 3000-4000 adolescents from consuming cannabis may only prevent 1 case of psychosis from emerging. This, the authors state, indicates that the “public health important of preventing cannabis to reduce schizophrenia or psychosis remains uncertain.”