Stimulants such as amphetamine, methamphetamine, cocaine and ecstasy are the most widely used illicit drugs after cannabis, and may influence the onset and course of psychosis. However, evidence about stimulant misuse in people with psychotic disorders is limited, because stimulant use is usually preceded by cannabis use, and both are associated with other personal and social risk factors. Therefore even large clinical studies of people with psychosis have often not examined the impacts of stimulants separately from those of cannabis. Epidemiological approaches, using population surveys and administrative health datasets, provide an additional method for studying the associations and impacts of stimulant drug misuse in people with psychosis.
This research addresses three questions. First, what is the prevalence of stimulant use disorders in people with psychosis? Second, what are the correlates of stimulant use disorders in people with psychosis, and how do they compare with people with psychosis who do not use stimulants? Third do stimulant use disorders influence the course of illness for people with psychosis?
The research examines three overlapping groups. Part 1 examines the rate and correlates of stimulant disorders in the Australian population, using data from the 2007 Australian National Survey of Mental Health and Wellbeing. Part 2 focuses on early psychosis, examining people admitted with psychosis to hospitals in New South Wales (NSW, population 7.2 million) over a 13 year period. It comprises three studies, examining (i) whether admission to hospital with psychoses is influenced by variations in stimulant availability in the NSW community, (ii) the prevalence and correlates of stimulant use disorders in people with a first admission for psychosis and (iii) the relationship between stimulant misuse and hospital readmission over two years. Part 3 examines enduring psychosis, using data from NSW hospital and community mental health services. It investigates the impact of stimulant use disorders on (i) diagnostic stability and progression to a diagnosis of schizophrenia and (ii) service use and social outcomes in people with schizophrenia. All studies measured and controlled for comorbid cannabis use disorders and potential personal and social confounders.
In the Australian population, the lifetime prevalence of stimulant disorders was 3.3%, and 12-month prevalence was 0.6%, equating to more than 97,000 Australians. Stimulant use disorders were most common in people with other risk factors for developing psychosis, including younger age, male gender, a family history of psychosis, earlier and more frequent use of cannabis, anxiety and depressive symptoms, and subclinical psychotic symptoms. Quarterly variations in amphetamine availability accounted for 50% of variation in the rate of admission for stimulant induced psychosis. People with first admission psychoses had stimulant use disorders at a rate more than ten times that of the age-matched Australian population. Stimulant use disorders were associated with diagnoses of brief and drug induced psychoses. Cannabis and stimulant disorders at first admission did not predict readmission, whereas prior admissions with stimulant disorders did. The associations of stimulant use disorders differed from those of cannabis use disorders. In the five years following admission for psychosis, comorbid stimulant use disorders were associated with diagnostic instability, reduced likelihood of diagnostic progression to schizophrenia and increased likelihood of revision of an initial diagnosis of schizophrenia to other conditions. By contrast, comorbid cannabis use disorders increased the likelihood of progression to schizophrenia. Fourteen percent (14%) of people admitted to hospital with diagnoses of schizophrenia had comorbid stimulant use disorders, and these were associated with physical health comorbidities, social dislocation and frequent use of mental health and emergency services. More than 80% of those with stimulant use disorders also had cannabis disorders: the risks of cannabis and stimulants appeared additive in this group.
In the Australian population and in Australians with psychosis, the rate of stimulant disorders is consistent with that reported from the US but higher than for many other developed countries. Around one in seven Australians with psychosis also has a stimulant use disorder, a rate at least ten times that of the general population. Because stimulants may precipitate or worsen acute psychotic symptoms, this suggests that they contribute to the overall burden of psychosis in Australia.
The associations of stimulant use disorders are distinct from those of cannabis use disorders. For people with early psychosis, stimulant disorders are associated with initial diagnoses of brief and drug-induced psychosis, lower rates of ongoing contact with specialist mental health services and lower rates of transition to a final diagnosis of schizophrenia. These findings are consistent with developmental and dimensional models of psychosis: stimulants are potent precipitants of acute psychotic symptoms and may therefore trigger psychotic symptoms in people with less personal vulnerability to the development of schizophrenia. An implication for clinical services is that stimulant-associated psychoses mark an important window of opportunity. Young people with stimulant-associated psychoses may have positive outcomes if they are supported in managing their substance use early in their illness. However, ongoing substance use is associated with high rates of relapse and readmission. For those people with schizophrenia, ongoing stimulant use disorders are associated with significant harms and frequent service use. More research is needed to identify effective interventions for this group.