Does Marijuana Use Cause Schizophrenia? (The New York Times):
“… The concern is focused largely on the link between heavy usage and psychosis in young people. Doctors first suspected a link some 70 years ago, and the evidence has only accumulated since then. In a forthcoming book, “Tell Your Children,” Alex Berenson, a former Times reporter, argues that legalization is putting a generation at higher risk of schizophrenia and other psychotic syndromes. Critics, including leading researchers, have called the argument overblown, and unfaithful to the science…
The debate centers on the distinction between correlation and causation. People with psychotic problems often use cannabis regularly; this is a solid correlation, backed by numerous studies. But it is unclear which came first, the cannabis habit or the psychoses. Children who later develop schizophrenia often seem to retreat into their own world, stalked periodically by bizarre fears and fantasies well outside the range of usual childhood imagination, and well before they are exposed to cannabis. Those who go on to become regular marijuana users often use other substances as well, including alcohol and cigarettes, making it more difficult for researchers to untangle causation…
The evidence so far indicates that one’s familial risk for psychotic disorders outweighs any added effect of cannabis use.”
A controlled family study of cannabis users with and without psychosis (Schizophrenia Research). From the abstract:
- BACKGROUND: Cannabis is one of the most highly abused illicit drugs in the world. Several studies suggest a link between adolescent cannabis use and schizophrenia. An understanding of this link would have significant implications for legalization of cannabis and its medicinal value. The present study aims to determine whether familial morbid risk for schizophrenia is the crucial factor that underlies the association of adolescent cannabis use with the development of schizophrenia.
- RESULTS: 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).
- CONCLUSIONS: The results of the current study suggest that having an increased familial morbid risk for schizophrenia may be the underlying basis for schizophrenia in cannabis users and not cannabis use by itself.
The Study in Context:
- Q: What do people with schizophrenia, bipolar disorder, depression, addiction, obsessive-compulsive disorder, and anxiety have in common? A: A brain with similar gray-matter loss