Drug Induced Psychosis by ROB POOLE and CLARE BRABBINS in British Journal of Psychiatry (1996), 168, 135-138
Intoxication mimicking functional psychosisThis refers to a direct pharmacological effect. There is no doubt that this occurs both with stimulants (Connell, 1958; Bell, 1965; Satel et al, 1991) and cannabis (Mathers & Ghodse, 1992). It probably also occurs with solvents, ecstasy and Iysergic acid diethylamide (LSD). Such states may persist for several days; it is not commonly appreciated that some of these substances have extremely long half lives. For example, amphetamine may persist in measurable quantities in the urine for up to 48 hours after a single small dose, and cannabinoids, even excluding active metabolites, persist in measurable quantities for up to 6 weeks.
True drug induced psychosisIf the term 'drug induced psychosis' has any utility it refers to psychotic symptoms which arise in the context of drug intoxication but persist beyond elimination of the drug. It only recurs if a subject is re-exposed to the drug, and it may be an idiosyncratic or dose-dependent syndrome. If drug induced psychosis is to qualify as a separate entity, it must have a different course and outcome to the
CausalityThe common clinical and scientific error is to uncritically assume that drug use, as an organic factor, is causal rather than symptomatic. This view has its origin in the hierarchical approach to diagnosis in psychiatry, and some authorities go as far as to suggest that a diagnosis of major psychosis should not be made in the presence of drug use. DSM-IV takes the converse position that a functional diagnosis should not be excluded unless there is compelling clinical evidence that the symptoms are entirely attributable to drugs. The latter position is to be preferred, as it is both in keeping with the limited scientific evidence and mitigates for clinical safety. If the symptoms are persistent and the individual cannot be persuaded to discontinue drug use, then causation may be irrelevant. Drawing a distinction between such patients and those with "real" mental illness is ethically questionable. Both types of patients suffer psychological distress and it is not the physician's role to moralise. It is important to recognise that, among the large group of drug users within the general population, a proportion will become mentally ill regardless of any supposed psychoto mimetic properties of drugs.
ConclusionsThe above coherent, empirical (though unproven) classification of adverse reactions to drug use offers the opportunity to discontinue use of the term 'drug induced psychosis', which is ambiguous and unsustainable. Other similarly ambiguous clinical terms have proven difficult to eradicate (e.g. "hysteria" and "formulation"). However, confused terminology leads to confused management, and the unrestrained spread of the drug epidemic demands the adoption of more rigorous thinking.