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12-04-2012 | Psychology | Article

Methamphetamine use may increase schizophrenia risk


Free abstract

MedWire News: Results from a population-based cohort study suggest that methamphetamine users are at increased risk for developing schizophrenia.

"Epidemiological studies have suggested that use of cannabis may increase the risk of developing schizophrenia," observe Russell Callaghan (Centre for Addiction and Mental Health, Toronto, Ontario, Canada) and team.

They add that "earlier literature, still controversial, suggests that abuse of methamphetamine could also trigger the development of persistent psychotic syndromes."

To investigate further, the researchers used data from California inpatient hospital discharge records for the period 1990-2000 to identify 42,412 patients with methamphetamine, 39,390 with cocaine, 408,604 with alcohol, 56,844 with opioid, 23,335 with cannabis-use disorders, and a comparison group of 188,732 patients with appendicitis.

The researchers note that appendicitis patients were selected as the comparison group because the condition is a common reason for hospital admission and "does not appear on theoretical grounds to be related to schizophrenia or substance use disorders."

None of the participants had a history of psychosis at the time of initial hospitalization. The primary outcome measure was readmission with a diagnosis of schizophrenia during the study period.

The researchers found that, compared with appendicitis patients, methamphetamine users had the greatest risk for schizophrenia (hazard ratio [HR]=9.37), followed by cannabis users (HR=8.16), cocaine users (HR= 5.84), those with alcohol-use disorder (HR=5.56), and opioid users (HR=3.60), after accounting for age, gender, ethnicity, and other variables.

All of the substance-use disorder groups had significantly greater risks for schizophrenia than the appendicitis group.

The difference in schizophrenia risk between methamphetamine users and those with cocaine, alcohol, or opioid-use disorders was also significant, while the difference between methamphetamine and cannabis users was not, the researchers note.

Callaghan and team conclude in the American Journal of Psychiatry: "Our findings add to the growing literature on cannabis as a risk factor for schizophrenia and, in addition, suggest that methamphetamine use sufficient to warrant a hospital diagnosis may also be a risk factor."

They add: "Schizophrenia can be a difficult diagnosis to establish, especially in chronic methamphetamine users, and clinicians need to be vigilant in monitoring their substance-abusing patients for signs of a developing persistent psychotic condition."

By Mark Cowen

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