Methamphetamine‐related psychosis: an opportunity for assertive intervention and prevention

Field: Medicine (Health Sciences)

Methamphetamine-related psychosis is a growing public health concern. All individuals with transient amphetamine-related psychotic symptoms should be considered to be at risk for future development of an enduring psychotic illness, and prioritized for early intervention of integrated care across substance use and mental health services. Reports of escalating methamphetamine use and dependence in Australia, the United States and more widely are highly concerning 1. Harmful physical and mental health consequences are common, including cardiovascular and cerebrovascular pathology, psychosis, suicide, anxiety and depression 2. Crystal methamphetamine is now the dominant form of methamphetamine used in global drug markets 3. Crystal methamphetamine has higher potency and may cause greater harms than other forms, analogous to the greater harms associated with high-potency 'crack' cocaine 4. As it is often injected or smoked, crystal methamphetamine reaches the brain readily, with rapid onset of effects 5. Methamphetamine dependence is associated strongly with injecting and smoking and with use of high-potency crystal methamphetamine 2, (> 60% purity in recent seizure estimates) 6. The growing use of crystalline forms of methamphetamine has increased concern about potential links with psychosis. The ability of amphetamine-related substances to induce transient psychotic symptoms such as auditory hallucinations and paranoid thinking has been known for more than 50 years 7. Pharmacologically, an association between meth/amphetamines and psychosis could be explained by their ability to powerfully increase synaptic dopamine levels 8. Models of schizophrenia suggest that repeated exposure to a dopaminergic stimulant gives rise to a hyperdopaminergic state that, in turn, may induce psychosis in vulnerable individuals 9. Transient psychotic symptoms are often seen as self-limiting or benign. Many individuals experiencing such symptoms do not seek help. Only a minority of methamphetamine users ever receive substance use treatment 10. Many delay help-seeking, and may not receive ongoing specialist care from mental health or addiction services. Where an individual does have contact with health services, if psychotic symptoms resolve within 24 hours of methamphetamine use a cross-sectional diagnosis of 'drug-induced psychosis' is likely to be made. Many clinicians will then discharge or, at best, adopt a 'watch and wait' approach to management. Contemporary views of psychosis challenge the simple categorical distinction between brief drug-induced psychoses and more enduring disorders such as schizophrenia. Psychoses are seen increasingly as heterogeneous disorders with a spectrum of illness profiles and course trajectories 11. Substantial evidence exists that diagnoses of drug-induced psychosis have poor predictive validity. A high proportion of people with diagnoses of drug-induced psychosis go on to receive a later diagnosis of schizophrenia. Follow-up studies have shown rates of transition to schizophrenia of more than 40% for cannabis-induced psychoses 12, 30% for amphetamine-induced psychoses 12 and more than 25% for mixed or unspecified drug-induced psychoses 13. In a recent Australian study of more than 7000 people, 46% of those admitted to hospital with diagnoses of drug-induced, brief or atypical psychosis later received diagnoses of schizophrenia 14. We propose here that the notion of a psychosis being 'drug-induced' is not a useful guide to care. Where transient or attenuated psychotic symptoms occur in the context of substance use, enduring psychosis may follow even where there is subsequent abstinence 15. The effect of substance use on psychosis risk may be influenced by multiple factors, such as age at first use, existing psychosis vulnerability and genotype 16. The interaction of substance use with other risk factors is undoubtedly likely to be complex: both may be shared effects of trauma or social isolation 17. Substance use may be a form of self-medication 18 and may both unmask and contribute to psychosis vulnerability. Large population-based studies demonstrate that, compared to matched controls, methamphetamine users have a significantly increased risk of schizophrenia 19. However, the risk of transition from brief or drug-induced psychoses to later schizophrenia may be less for amphetamines than for cannabis 12, 14. Therefore, methamphetamine-related psychosis presentations are important opportunities to prevent the potential development of disabling chronic psychotic illness. Currently there is limited evidence to guide clinicians in appropriate management of methamphetamine-related psychoses. We propose that the model of early intervention in people at risk of psychosis should be applied. All such individuals need careful assessment, including family history of psychosis, personal risk factors for psychosis (trauma, head injury, intellectual disability, subtle learning or motor problems) and past subclinical psychotic symptoms. For someone who continues to experience unusual beliefs or perceptions for days or weeks after use, it may be prudent to commence treatment and assertive follow-up, even where symptoms are attenuated or atypical. To enable effective management of such an individual, there is a need for flexible and integrated care provision across mental health, substance use and primary care services. For example, provision of specialist psychiatric consultation within substance use and primary care services is likely to increase detection of early psychotic illness through endorsement of psychotic symptoms as a serious concern, rather than a benign consequence of use. Psychiatric liaison would additionally enable immediate access to treatment and education of staff and clients about mental health concerns. There are, of course, many challenges in providing such care. Assessment is complicated frequently by continued use of methamphetamine or other drugs, providing no period of abstinence for observation. People with comorbid psychosis and methamphetamine use often exhibit intermittent service use, and may not persist with psychological or pharmacological treatments. Flexible and coordinated service models that integrate mental health and substance use services are required. There is a need for increased capability in detection and treatment of methamphetamine use among mental health clinicians and in the detection of early signs of psychotic illness by substance use clinicians. Escalating numbers of methamphetamine-related psychosis presentations present a huge burden to clinical services. In an era when methamphetamine use and related harms continue to rise, this burden must be addressed urgently. Early intervention for methamphetamine-related psychotic symptoms should be prioritized across all services, with emphasis on understanding an individual's drug use, mental health and the inter-relationship of these factors. Research efforts should focus upon identifying effective and acceptable treatment strategies in these difficult-to-access individuals with complex needs. None.