Researchers have known for many years that there is a link between marijuana and schizophrenia. Many of the studies, however, are inconclusive or contradict previous research.

Facts about schizophrenia

Schizophrenia is a severe chronic mental health disease that affects approximately 1 percent of the population and afflicts men and women in equal proportions, according to the National Institute of Mental Health. Onset with hallucinations and delusions usually begins between the ages of 16 and 30, and men typically have a slightly earlier onset than women.

The link between marijuana and schizophrenia

Multiple studies have indicated higher rates of marijuana use in individuals with schizophrenia, typically twice the rate of those without the disease. Some researchers postulate that the opposite is also true: marijuana users have twice the probability of developing schizophrenia. This latter suggestion has conflicting research, some supporting the theory and others refuting it.

Genetics

Researcher Marie-Odile Krebs, psychiatry professor at the National Institute of Health and Medical Research lab in France, studied individuals with schizophrenia. She discovered that among those who also used marijuana, more than a third “either developed schizophrenia within a month of beginning to smoke pot or saw their existing psychosis severely exacerbated with each successive exposure to the drug.” In addition, the patients in this group had an earlier onset of the disease and were diagnosed with schizophrenia three years prior to those in the other group.

Gender seemed to play a significant role in this link between marijuana and schizophrenia, based on her study. She also found that in the group with the higher affinity for earlier-onset schizophrenia, there was a strong family history of psychosis. Krebs stated that “those in the former group had three times the number of close relatives with psychotic disorders.” These results led Krebs to postulate that “early exposure may have critically altered the development of brain receptors affected by marijuana.”

Brain receptors and marijuana

Endocannabinoid receptors are specific neuroreceptors in the brain which affect the dopamine system and neuron responses. Anything that changes these receptors, such as marijuana, can affect the dopamine receptors and leave a higher level of circulating dopamine, which could trigger psychosis.

Stimulants such as cocaine and amphetamines can increase the dopaminergic effects, resulting in psychosis. Other antipsychotic drugs act by blocking these dopamine receptors and thus decrease periods of psychosis.

Cognition and marijuana

In a study by Pamela DeRosse at Long Island’s Feinstein Institute for Medical Research, results indicated that schizophrenic patients who used marijuana “had faster brain processing speed, greater verbal ability and better memory than patients who didn't smoke — not attributes usually associated with being high.”

Marijuana has various effects in individuals with schizophrenia, some more positive than others, and the chemical make-up of marijuana is the cause of this variation in responses. The THC part of marijuana causes hallucinations, paranoia and psychotic episodes. Yet a secondary ingredient, CBD or cannabidiol, works to reduce psychosis.

If a new drug could be developed utilizing the antipsychotic properties of CBD while blocking the THC effects, there is potential for its use in the treatment of the schizophrenic patient population.