A drug-induced psychosis alone, without evidence of a separate underlying pathological infirmity of the mind, does not constitute a 'disease of the mind' for the purposes of the common law defence of mental illness. Evidence that some persons who ingest drugs may be vulnerable to developing psychosis is insufficient to establish the defence. The psychiatric opinions must be supported by independent evidence, not merely the unproven history given by the accused, particularly where that history is subject to a s 136 Evidence Act limitation.
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