Quote:
Originally Posted by blueash
The Harvard study was an attempt to work around the known confounding factors in studying drug use and later psychiatric outcomes. It has been long known that heavy drug and alcohol use is associated with poorer adult functioning. But correlation is not causation. So in this study of only about 300 people they divided the 300 into four groups. 87 people non-psychotic and not drug users, 84 non-psychotic drug users, 76 psychotic drug users, and 32 psychotic non drug users. The study then looked at the family history of nearest relatives of each person and found that "There was an increased morbid risk for schizophrenia in relatives of the cannabis using and non-using patient samples compared with their respective non-psychotic control samples (p = .002, p < .001 respectively). There was no significant difference in morbid risk for schizophrenia between relatives of the patients who use or do not use cannabis (p = .43)." What this means is that if you have a family history of psychosis your risk of becoming psychotic is increased whether you use pot or not.
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Your last sentence is correct. However, you forgot to mention that if you are a regular pot smoker, your risk of developing a psychosis is doubled.
Correlation is not causation: That's what the tobacco companies used to say about cigarette smoking and lung disease.