We have discussed in this newsletter about how marijuana, in some people, can cause psychosis. This usually occurs with a very potent strain of cannabis (>30% THC). However, it is important to remember that this psychosis is temporary, and can be caused by a number of substances (caffeine, nicotine, alcohol, stimulants, and, obviously, hallucinogens).
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Psychosis is defined by the Diagnostic and Statistical Manual of Mental Disorders (DSM) broadly as a “gross impairment in reality testing” or “loss of ego boundaries” that interferes with the capacity to meet the ordinary demands of life. The Boston Globe defines drug-induced psychosis as "temporary disorientation that resembles a waking dream, with odd, imagined sights and sounds, often accompanied by paranoia or an ominous sensation".
However, while as scary this may be, it is most likely not associated with schizophrenia. Schizophrenia is not a uniform disorder but more of an umbrella term for an array of unexplained problems involving recurrent psychosis and other common symptoms. It is "most likely" because the field is still mixed. For instance, Dr. Margaret Haney, a professor of neurobiology at Columbia University Medical Center has stated: “I’ve been doing this research for 25 years, and it’s polarizing even among academics.”
Schizophrenia is a disease with premorbid symptoms (symptoms that show up before the official diagnosis) such as low affect (emotion), documented changes in brain volume, and is linked to a host of putative genetic mutations. It also is more prevalent in males. Nevertheless, many studies suffer from the "correlation is not causation" effect. Many people who develop schizophrenia (which does not clinically appear until your early 20's) may have smoked marijuana. It is the most widely used illicit substance in the US after all. Yet this still does not mean that marijuana caused schizophrenia.
The field's consensus, as of now, is that marijuana use can exacerbate schizophrenic symptoms and could accelerate the diagnosis of schizophrenia. In other words, people with predictors of developing schizophrenia (family history, premorbid symptomology, being male) have a predisposition for a diagnosis of schizophrenia after smoking cannabis. Most marijuana users start in their late teens and early 20's, so the timing makes it easy to connect the two together.
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Essentially, the theory is that people who are likely to develop schizophrenia will develop it quicker if they use marijuana. An important message to carry away from this theory is the fact that it identifies another subpopulation (in addition to adolescents) that should stay away from pot. The trouble is there is no test that will tell you that you will develop schizophrenia, even if you have it in your family. So you cannot be sure whether the cannabis caused the schizophrenia, or whether you would have developed schizophrenia anyway and the weed merely hastened its arrival (which is still not a good outcome).
Interesting fact: do you know which drug is most heavily correlated with schizophrenia? Nicotine. About ninety percent of schizophrenic patients smoke cigarettes. But we already know that cigarettes are bad for you, so this does not seem as concerning as to whether cannabis contributes to the disease. Furthermore, these patients may be smoking to ease symptoms, as the cholinergic system in the brain (which nicotine activates) may be involved in the symptoms of schizophrenia.
The best advice (from your's truly) for folks who are concerned about developing schizophrenia is, if you have a known psychotic disorder or if schizophrenia runs in your family, you may want to rethink smoking that joint.
Sources: LabRoots.com, BostonGlobe.com, Behavioral Neurology and Neuropsychiatry, www.drugabuse.gov, Rosenberg's Molecular and Genetic Basis of Neurological and Psychiatric Disease (Fifth Edition), New England Journal of Medicine, www.WebMD.com, Current Psychosis & Therapeutics Reports, European Archives of Psychiatry and Clinical Neuroscience