Among individuals with psychosis who are also heavy marijuana users, the age they first used marijuana is strongly linked to the age of their first bout of psychosis, according to a study of 57 patients.
Although marijuana use by itself is neither sufficient nor needed to trigger schizophrenia, “if cannabis use precipitates the onset of psychosis, efforts should be focused on designing interventions to discourage cannabis use in vulnerable individuals,” Dr. Juan A. Galvez-Buccollini and his associates said.
This caution pertains to someone with a first-degree relative with psychosis, which is “the highest risk factor for schizophrenia,” said Dr. Lynn E. Delisi, senior investigator for the study, a psychiatrist at the Boston VA Medical Center in Brockton, Mass., and professor of psychiatry at Harvard Medical School, Boston.
If someone had a first-degree relative, “I would caution them about the consequences of cannabis use and the association with schizophrenia,” she said.
Findings from previous research has shown that marijuana use is associated with an earlier age of psychosis onset in people abusing multiple substances, but studies have not looked at a possible link between the onset of cannabis use itself and resulting psychosis.
Because of this, Dr. Galvez-Buccollini, a psychiatry researcher at VA Boston Healthcare System and Harvard, and his colleagues interviewed 57 patients with a current diagnosis of schizophrenia, schizoaffective disorder, schizophreniform disorder, or psychosis not otherwise specified, who also had a history of heavy cannabis use before the onset of psychosis. They defined heavy cannabis use as 50 or more uses during a one year period.
Average age of the subjects was 25 years with a range of 18-39 years. Of the total, 83 percent were men, and 88 percent were not married. The average age of psychosis onset was 22 years, and the average age for first psychosis-related hospitalization was 23.
Schizophrenia was the most common psychosis (42 percent), followed by schizoaffective disorder (32 percent). The average age of first marijuana use was 15, preceding psychosis onset by an average of 7 years.
During the study period, the prevalence of daily cannabis was 59 percent with another 30 percent reporting use 2-5 days per week, and the remaining 11 percent reporting weekly use. Alcohol abuse was 16 percent and alcohol dependence was 8 percent.
The researchers found a statistically significant link between the age when cannabis use first started and the age when psychosis was first diagnosed. This association was consistent after researchers excluded patients with any diagnosis of alcohol abuse or dependency during their lifetime.
The analysis also showed a strong link between the time a patient first smoked marijuana and their age of first psychosis hospitalization.
Marijuana affects dopamine receptors and can have other neurochemical effects.
“There are two components of cannabis, one that potentiates and another that antagonizes psychotic symptoms,” said Delisi. The balance between these two effects can differ among various strains of cannabis, she added.
Source: Schizophrenia Research