Modern scientific research has firmly established that some people who use large amounts of marijuana or other forms of cannabis increase their odds of experiencing psychosis, one of the major symptoms of schizophrenia and several other severe mental illnesses. Research also indicates that the link between cannabis use and schizophrenic or psychotic states of mind may have at least a partially genetic basis. In a study published in June 2014 in the journal Molecular Psychiatry, a team of British and Australian researchers sought to uncover the genetic risk profile that connects cannabis intake and schizophrenia. These researchers concluded that the genetic risk apparently runs in both directions, from cannabis use to schizophrenia and from schizophrenia to cannabis use.
Cannabis, Psychosis and Schizophrenia
Psychosis is a debilitating mental state centered largely on sensory hallucinations and the establishment of a delusional thought pattern that features highly illogical, firmly held beliefs and points of view. People affected by schizophrenia commonly have prominent psychosis symptoms. Other mental and physical health problems that can produce a psychotic state of mind include brief psychotic disorder, certain forms of depression and bipolar disorder, certain personality disorders, strokes, epileptic disorders and Alzheimer’s disease and other forms of dementia.
Psychosis is also linked to the active use of certain substances, as well as the withdrawal syndromes that commonly appear when a dependent or addicted substance user ceases his or her intake of drugs or alcohol. In the context of marijuana/cannabis use, psychosis typically appears temporarily in some individuals who consume large amounts of the drug on single or multiple occasions. In a person with known or undetected symptoms of schizophrenia, a chronic pattern of heavy use can produce increasing levels of psychosis-related mental incapacitation. Conversely, people affected by schizophrenia have an increased tendency to use marijuana/cannabis or other mind-altering substances. Overall, cannabis users have a roughly 100 percent greater chance of having schizophrenia (a rare condition affecting only 1 percent of the adult population) than people who don’t use drugs.
The Influence of Genes
Some people are genetically prone to use addictive substances and to experience significant problems related to that substance use. However, the connection between substance use, substance addiction and genetics is complex. Instead of stemming from a single gene, substance-related risks stem from the interaction of multiple genes that exert their influence in different ways. In addition, genetic risks for substance use and addiction interact with non-genetic risks that appear in each person’s surrounding environment as he or she grows older. Genes also play a role in the onset of schizophrenia. However, as with substance use and addiction, the interaction between genetic risk factors for the mental illness is complex and heavily intertwined with non-genetic environmental risks.
Shared Cannabis and Schizophrenia Risks
In the study published in Molecular Psychiatry, researchers from King’s College London and Australia’s Queensland Institute of Medical Research used an examination of 2,082 people to explore the genetic risks underlying the connection between marijuana/cannabis use and schizophrenia. All of the study participants were free from diagnosed mental illness; in addition, 1,011 of the participants had a history of using some form of cannabis. The researchers assembled a schizophrenia risk profile for each individual based on the known genetic factors involved in the onset of the disorder. The chief variable in this profile was the number of identified schizophrenia-related genes.
When the researchers compared the schizophrenia profiles to the cannabis use histories of each study participant, they found that those individuals with increased genetic risks for the mental illness had a substantially higher rate of involvement in cannabis intake. In addition, among cannabis users, participants with heightened genetic risks for schizophrenia also used larger amounts of cannabis than their counterparts with lower genetic risks. However, the researchers could not definitively determine the direction of the association between cannabis use and schizophrenia. In fact, they believe that the same genetic factors that make a person susceptible to schizophrenia may also make that person unusually likely to start using some form of cannabis.
The study’s authors note that their findings highlight the complicated nature of the relationship between the genetic and non-genetic risks for drug use and mental illness. Other factors in this complex equation include the specifics of each individual’s personality (itself a product of genetic and environmental influences) and the behavioral choices made over the course of a lifetime.