Methamphetamine and other amphetamine-type stimulants are the second most common type of illicit drug used worldwide. "We found that people hospitalised for methamphetamine dependence who did not have a diagnosis of schizophrenia or psychotic symptoms at the start of our study period had an approximately 1.5 to 3.0-fold risk of subsequently being diagnosed with schizophrenia, compared with groups of patients who used cocaine, alcohol or opioid drugs," says Doctor Russ Callaghan. Callaghan also found that the increased risk of schizophrenia in methamphetamine users was similar to that of heavy users of cannabis.
To establish this association, the researchers examined California hospital records of patients admitted between 1990 and 2000 with diagnosis of dependence or abuse for several major abused drugs: methamphetamine, cannabis, alcohol, cocaine or opioids. They also included a control group of patients with appendicitis and no drug use. The methamphetamine group had 42,412 cases, while cannabis had 23,335.
Records were excluded if patients were dependent on more than one drug or had a diagnosis of schizophrenia or drug-induced psychosis during their initial hospitalisation. Readmission records within California hospitals were analysed for up to 10 years after the initial admission. The researchers then identified patients who were readmitted with a schizophrenia diagnosis in each drug group.
There has been a longstanding debate as to whether there is a connection between methamphetamine use and schizophrenia. Many Japanese clinicians have long believed that methamphetamine might cause a schizophrenia-like illness, based on their observations of high rates of psychosis among methamphetamine users admitted to psychiatric hospitals.
However, they lacked long-term follow-up studies of methamphetamine users initially free of psychosis. In North America, this link has mostly been discounted, as psychiatrists believed that the psychosis was already present and undiagnosed in these methamphetamine users.
"We really do not understand how these drugs might increase schizophrenia risk," says Doctor Stephen Kish. "Perhaps repeated use of methamphetamine and cannabis in some susceptible individuals can trigger latent schizophrenia by sensitising the brain to dopamine, a brain chemical thought to be associated with psychosis." Kish also cautions that the findings do not apply to patients who take much lower and controlled doses of amphetamines or cannabis for medical purposes.
MEDICA.de; Source: Centre for Addiction and Mental Health