Daily Pot Smoking May Hasten Onset of Psychosis

http://www.sciencedaily.com/releases/2009/12/091220144936.htm

ScienceDaily (Dec. 20, 2009) - Progression to daily marijuana use in adolescence may hasten the onset of symptoms leading up to psychosis, an Emory University study finds. The study was published in the November issue of the American Journal of Psychiatry.

The researchers analyzed data from 109 hospitalized patients who were experiencing their first psychotic episode. The results showed that patients who had a history of using marijuana, or cannabis, and increased to daily pot smoking experienced both psychotic and pre-psychotic symptoms at earlier ages.

"We were surprised that it wasn't just whether or not they used cannabis in adolescence that predicted the age of onset, rather it was how quickly they progressed to becoming a daily cannabis user that was the stronger predictor," said Michael Compton, lead author and assistant professor of psychiatry in the Emory School of Medicine.

The study also found a gender difference: The female subjects who progressed to daily pot smoking had a greater increased risk for the onset of psychosis than the males.

Marijuana is the most abused illicit substance among people with schizophrenia, the most extreme form of psychosis, and previous research has shown that smoking pot is likely a risk factor for the disease.

The Emory study also focused on what is known as the prodromal period, when a person has symptoms such as unusual sensory experiences, which are often precursors to frank hallucinations and delusions. Prodromal symptoms can occur months, or years, before a diagnosis of psychosis.

About 30 to 40 percent of prodomal teenagers will eventually develop schizophrenia or another psychotic disorder.

"The prodromal period is especially important because it's considered to be a critical time for preventive intervention," says Elaine Walker, a co-investigator of the study and professor of psychology and neuroscience at Emory.

The study also involved researchers from Emory's Rollins School of Public Health and Georgia State University. It was funded by the National Institute of Mental Health.

Journal Reference:

Compton et al. Association of Pre-Onset Cannabis, Alcohol, and Tobacco Use With Age at Onset of Prodrome and Age at Onset of Psychosis in First-Episode Patients. American Journal of Psychiatry, 2009; 166 (11):

1251-57

http://ajp.psychiatryonline.org/cgi/content/abstract/166/11/1251

OBJECTIVE: Several reports suggest that cannabis use is associated with an earlier age at onset of psychosis, although not all studies have operationalized cannabis use as occurring prior to onset of symptoms.

This study addressed whether pre-onset cannabis use, alcohol use, and tobacco use are associated with an earlier age at onset of prodromal and psychotic symptoms. Effects of the progression of frequency of use were examined through time-dependent covariates in survival analyses.

METHOD: First-episode patients (N=109) hospitalized in three public-sector inpatient psychiatric units underwent in-depth cross-sectional retrospective assessments. Prior substance use and ages at onset of prodromal and psychotic symptoms were determined by standardized methods, and analyses were conducted using Cox regression modeling.

RESULTS: Whereas classifying participants according to maximum frequency of use prior to onset (none, ever, weekly, or daily) revealed no significant effects of cannabis or tobacco use on risk of onset, analysis of change in frequency of use prior to onset indicated that progression to daily cannabis and tobacco use was associated with an increased risk of onset of psychotic symptoms. Similar or even stronger effects were observed when onset of illness or prodromal symptoms was the outcome. A gender-by-daily-cannabis-use interaction was observed; progression to daily use resulted in a much larger increased relative risk of onset of psychosis in females than in males.

CONCLUSIONS: Pre-onset cannabis use may hasten the onset of psychotic as well as prodromal symptoms. Age at onset is a key prognostic factor in schizophrenia, and discovering modifiable predictors of age at onset is crucial.