Mental Health help | 3 yr. onset increase for psychosis with cannabis use study

Mental Health help | People with schizophrenia who use cannabis develop the disease three years earlier, on average, than non-cannabis users, according to new findings first published in Schizophrenia Research."It seems that for some individuals, use of cannabis may forward the onset of psychosis by several years. Thus, young people who are vulnerable for psychosis should be warned of the effects of cannabis use," Dr. Siri Helle and Dr. Else-Marie Loberg of Haukeland University Hospital in Bergen, Norway, two of the study's authors, told Reuters Health by email.

Past research has linked substance use, especially cannabis, to an earlier disease onset in schizophrenia spectrum disorders, Dr. Helle and her colleagues write, but most studies have been too small to determine the effects of specific substances.

One meta-analysis found people who used unspecified substances had a two-year earlier disease onset, while those who used cannabis developed schizophrenia 2.7 years earlier.

Factors like gender and family history of psychosis may confound the relationship, to better understand the effect of use of specific substances on age at schizophrenia onset, the researchers looked at 1,119 patients from three cities in Norway who had been diagnosed with schizophrenia and screened for history of substance use.

Among the 627 individuals with a substance use history, the average age at schizophrenia onset was 23, versus 25.9 for those with no history of substance use.

Nine out of 10 of the substance users reported using cannabis. Analyses of individual substances, including alcohol, only found a significant association of age at disease onset with cannabis. Family history of psychosis was not associated with age at onset, nor was it linked with cannabis use. There also was no association between gender and age at disease onset or cannabis use.

"The mechanisms by which exposure to cannabinoids increase the risk for developing a psychotic disorder are not fully understood," Dr. Helle and Dr. Loberg told Reuters Health. "The most plausible explanation for an earlier onset of psychosis is that use of cannabis has influenced the brains' functioning and transmitter systems, enabling a psychotic episode to take place. Experimental studies have shown that ‘delta-9 tetrahydrocannabinol' or 'THC' may induce psychotic symptoms and transient cognitive symptoms in otherwise healthy people.

There are, however, now several hypotheses that emphasize the role of cannabinoids on the neuro-developmental processes relevant to psychotic disorders.”

Other key questions to address, according to the researchers, include the influence of cannabis on treatment response, and how environmental and genetic risk factors for schizophrenia may interact with cannabis use.