Methamphetamine-induced Psychosis and Mental Impairment: A Challenge from New Zealand

While knowledge about chronic amphetamine-induced psychosis and its similarity to schizophrenia is at an early stage, its incidence and ramifications are posing a serious issue for the criminal law. The condition has the potential in principle to result in findings of insanity/mental impairment and diminished responsibility, as well as to be significantly mitigating at the time of sentencing. However, difficult legal questions arise as to whether an ongoing (as against transient) chronic methamphetamine-induced psychosis constitutes a "disease of the mind" as well as complex public policy issues by reason of the condition being self-induced. This column reviews the law generally on the subject, as well as the ruling by Jagose J in R v Brackenridge [2019] NZHC 1004, and explores the ramifications of the reasoning in the ruling for decisions by courts outside New Zealand. It calls for further and more nuanced analysis of the ramifications of drug-induced psychoses being self-induced in the context of the law on criminal responsibility and culpability.