Polydrug use is common, and increases the risk of negative health effects (1). A study that investigated all (N = 194) overdose deaths in Norway in 2012 found an average of 4.9 different drugs per autopsy (2). The study concluded that drugs taken in combination (especially opioids + benzodiazepines) are the main cause of fatal overdose. Mono-intoxication with heroin was not detected in any of the 194 fatal overdoses (2).
Reporting of overdose is largely based on ICD-10, the international statistical classification of diseases and related health problems (3). A single substance, for example heroin, is typically chosen as the main cause of death (2). This gives a wrong impression, because drug-related deaths are rarely caused by one single drug (4). Our impression is that most overdose deaths are due to a pattern characterised by chaotic use of several different drugs. Polydrug use is also associated with poor prognosis, higher rates of comorbidity with other mental disorders (5), and higher demands on the content and length of treatment (1, 5).
Multiple drug dependence can be coded with the ICD-10 diagnosis F19 (3), but the threshold for using this diagnosis appears to be high. The guide for F19 states: 'Only in cases in which patterns of psychoactive substance taking are chaotic and indiscriminate, or in which the contributions of different drugs are inextricably mixed, should code F19.- be used.'. It appears that the strict criteria for diagnosis of multiple substance dependence will be phased out in the future. ICD-11 (6) is scheduled to replace ICD-10 from 2022. According to ICD-11, multiple substance dependence should be coded with 6C4F, regardless of pattern of use.
In normal clinical practice, the F19 diagnosis can be a useful indicator of elevated risk and treatment requirements. However, we had the impression that chaotic drug use occurred more often than it was recorded. This study investigates substance dependence diagnoses in a selection of inpatients that had received specialised, interdisciplinary addiction treatment. The prevalence of ICD-10 diagnosis F19 recorded in the patient records was compared with the prevalence of F19 following a review of the records.