CHICAGO – The idea that cannabis use might trigger a patient’s first psychotic episode is one that needs to be taken seriously, Dr. John Csernansky said at a seminar on "Reinventing Inpatient Psychiatry."
"Are there patients out there who have schizophrenia who would not have had it without substance abuse? There may be," said Dr. Csernansky, chairman of the department of psychiatry and behavioral sciences at Northwestern University, Chicago. "This is a very hot topic and one that is genuinely frightening."
Cannabis use is frequent within 1-2 years before the first psychotic break. A variety of epidemiological studies suggest that cannabis use in adolescence (15-18) increases the risk for development of schizophrenia, even years later. A meta-analysis published earlier this year (Arch. Gen. Psychiatry 2011;68:555-61) provides evidence of a relationship between cannabis use and earlier onset of psychosis. The meta-analysis, which included data from 83 studies, found that the mean age of psychosis for cannabis users was 2.70 years younger than for nonusers. More than 8,000 patients who reported using psychoactive substances and more than 14,000 who did not were covered by the meta-analysis.
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Some studies suggest that cannabis use as a young adult can increase the risk of developing schizophrenia.
The connection between cannabis use and early psychosis is particularly concerning because substance abuse is common in schizophrenia. Cannabis, in particular, has a severe effect on the thalamus of the person with schizophrenia. This effect is worse than the effect of alcohol.
"It looks as though alcohol makes schizophrenia worse, whereas cannabis damages a part of the brain that maybe otherwise would have not been [damaged]," Dr. Csernansky said.
If cannabis is used before the first psychotic episode, it "piles on damage," Dr. Csernansky said. A study of a group of prodromal subjects found ventricular volume increased with cannabis abuse and much less with alcohol abuse. Similar relationships were not observed with the use of nicotine.
There may be a familial contribution to the propensity to use drugs on top of severe mental illness, said Dr. Csernansky. When discordant sibling pairs, with and without schizophrenia, were assessed for lifetime history of substance use disorders, the nonpsychotic siblings of schizophrenia patients had higher rates of cannabis and alcohol abuse.
"Something about having [schizophrenia] in your family puts you at risk for more substance abuse," he said.
Dr. Csernansky receives consulting fees as a consultant on the data monitoring committee for Sanofi-Aventis and Eli Lilly.