By Richard Lenti
With the growing use of medical marijuana to treat chronic pain and other health problems, the debate over the medical effects of the drug on the human mind continue to make their way through the medical community.
The latest salvo comes from researchers in Australia and England. At the center of the debate is the possible relationship between marijuana (cannabis) and mental illnesses such as schizophrenia.
In a pair of articles published in F1000 Medicine Reports, the authors were given the unique opportunity to read the opposing side’s drafts and consider their arguments when structuring their own article.
In his article “Cannabis and psychosis: what causes what?” David Castle of the University of Melbourne argues that a clear link exists between cannabis use and an increased risk of psychotic symptoms.
“There is little doubt that ingestion of the plant Cannabis sativa can cause positive psychotic-like symptoms.” Castle writes. “A rather more contentious issue is whether cannabis can actually cause schizophrenia. This, of course, is very difficult to determine definitively.”
“It is clear that cannabis and related compounds can cause acute transient impairments in memory, attention, and executive function. But whether exposure to cannabinoids is associated with persistent cognitive deficits is not as clear.”
Castle cites one study that indicated people with schizophrenia had a lifetime rate of cannabis exposure of 97 percent – meaning almost all of them have tried the drug. Yet, he also notes that most people who use cannabis do not develop schizophrenia, and that many people diagnosed with schizophrenia have never used cannabis.
“Therefore, it is likely that cannabis exposure is a ‘component cause’ that interacts with other factors to ‘cause’ schizophrenia or other psychotic disorders, but is neither necessary nor sufficient to do so alone,” Castle wrote.
However, the authors of the accompanying article are not as convinced that the prevailing scientific evidence proves a relationship exists between pot use and schizophrenia.
“Schizophrenia is a serious illness associated with substantial loss of quality of life, social and economic problems, co-morbidity and premature mortality,” they write, “and the need to improve primary prevention is paramount.”
But for Suzanne Gage, Stan Zammit and Matt Hickman of the Universities of Bristol and Cardiff, they say that from a scientific perspective, the extent to which the use of cannabis leads to an increased risk of schizophrenia remains uncertain.
In fact, they point out that some empirical comparisons of cannabis use and schizophrenia indicates just the opposite.
“There is evidence that cannabis use in many developed countries has increased greatly over the past 40 years. For example, in the United Kingdom, cannabis use has risen 10-20 fold since the 1970s,” they write. “However, recent data on new admissions for schizophrenia have shown no increase at all; indeed, there is a suggestion of a downward trend in diagnoses.”
They argue that more robust evidence is required to determine whether preventing cannabis use will have any substantial impact on preventing psychotic disorders in the population, or within specific high-risk subgroups.
Both sides agree that cannabis is a public health concern and that the public should be made fully aware of the risks associated with using the drug.
This particularly applies, Castle writes, to those who have a family history of schizophrenia or who have experienced psychosis-like symptoms, as they may be at greater risk.
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