The Legend: Smoking marijuana increases the risk for developing schizophrenia or other mental illnesses.
Status: False
Analysis:
Research connecting marijuana use to mental illnesses such as schizophrenia is a good example of how media reports confuse correlation with causation. Correlation means observing that two variables seem to occur together. Causation means that changing one variable always causes changes in the other variable. A correlation would be noticing that there seems to be a higher rate of schizophrenia among marijuana smokers. Causation would be saying that marijuana smoking causes schizophrenia. Correlation is where research begins; causation is where you hope your research will end.
In the late 1980's, a piece of research published in the medical journal Lancet observed that chronic marijuana smokers were twice as likely to be schizophrenic - a correlation, (Andreasson et al, 1987). The study did not suggest that smoking marijuana had caused the schizophrenia. In fact, scientists have pointed out that there has been no increase in the rates of schizophrenia in those areas where there is heavy marijuana use, an increase you would expect to see if marijuana smoking did cause schizophrenia.
It is now believed that marijuana use may trigger an earlier onset of schizophrenic symptoms in those individuals that are already predisposed. It has also been reported, by the users themselves, that in some cases marijuana can ease their psychotic symptoms. This could account for the higher rate of marijuana use among people with schizophrenia. The marijuana didn't cause their schizophrenia, the schizophrenia is what led to their self-medication of symptoms with marijuana, (Warner, 1994). big difference.
The greatest risk factor for schizophrenia is family genetics. If this type of mental illness is in your family you might want to reconsider your marijuana usage.
