‘Drug induced psychosis' is a commonly used clinical label but lacks a universally accepted definition. Psychiatrists' understanding of the term was examined using a specifically designed questionnaire. Knowledge about the effects of drugs of abuse and their relationship with psychosis was also examined. A substantial proportion of clinicians did not have a logical and coherent scheme for understanding ‘drug-induced psychosis' and there was no consensus as to which reactions to drug taking should be included within the rubric. Diagnostic errors have potentially serious consequences, so lack of knowledge in this area needs attention and a proposed classification is given.