AbstractAt present, the law draws a distinction when assigning criminal responsibility to those who commit offences while experiencing psychotic symptoms: if the symptoms are believed to arise because of ingesting drugs (an external cause), the offender is generally convicted of the offence; if the symptoms arise from a mental illness (an internal cause), the offender may be afforded a defence of insanity. In practice, drawing such a distinction can be problematic. There are difficulties for example in determining criminal responsibility when the use of drugs is followed by the emergence of a psychotic illness process that then continues to have an independent existence even in the absence of the ongoing substance use. This article analyses legal, policy, and expert witness perspectives relating to liberal, conservative, and intermediate approaches to this problematic area of jurisprudence. Copyright © 2008 John Wiley & Sons, Ltd.