Epidemiology of hospitalizations with hallucinogen use disorder: a 17-year U.S. National study

Hallucinogens produce marked alterations in thought, perception and mood and are commonly grouped into serotonergic (tryptamine- and phenethylamine-like), N-methyl-D-aspartate (NMDA) antagonist, and other classes. Although hallucinogen use disorder is relatively uncommon compared with alcohol or opioid disorders, it nevertheless contributes to inpatient healthcare burden; in 2012 hallucinogen use disorders ranked among the top five substance-related diagnoses for adult inpatient stays in the USA. Previous prevalence estimates cited by the authors put past-year hallucinogen use disorder at about 0.06% and lifetime prevalence at about 0.6%, but national data on hospitalisation trends and inpatient outcomes for this disorder have been lacking. Singh set out to describe national time-trends in hospitalisations with hallucinogen use disorder in the USA over a 17-year period, to quantify associated healthcare utilisation and in-hospital mortality, and to identify patient and hospital factors associated with worse outcomes. The study aimed to fill the gap in epidemiological knowledge about the hospital burden of hallucinogen use disorder and to highlight potential targets for interventions or policy measures.

The investigators used the 1998–2014 U.S. National Inpatient Sample (NIS), a nationally representative, de-identified, all-payer database that is a 20% stratified sample of hospital discharges. Hospitalisations with hallucinogen use disorder were identified using ICD-9-CM diagnostic codes; the study cohort included records where hallucinogen use disorder appeared as a primary or secondary diagnosis. To improve specificity, the researchers excluded records with codes indicating drug use in remission, drug addiction counselling, or drug rehabilitation/detoxification. Primary descriptive metrics were national rates of hallucinogen use disorder hospitalisations per 100,000 NIS claims and in-hospital mortality per 100,000 NIS hospitalisations, calculated across multi-year intervals. The study also assessed three healthcare utilisation outcomes: median hospital charges, length of stay above the median (defined as more than 3 days), and discharge to a non-home destination (short-term hospital, skilled nursing or intermediate care facility), the latter being used as an indicator of need for more intensive post-hospital care. For associations between patient and hospital characteristics and outcomes, multivariable-adjusted logistic regression models were fitted. Predictor variables included demographics (age, sex, race), comorbidity measured by the Deyo-Charlson index (a standard comorbidity score), insurance payer type, income, hospital region, urban versus rural setting, and hospital bed size. Results were reported as odds ratios (OR) with 95% confidence intervals (CI). The Methods text did not specify adjustment of hospital charges for inflation; later the authors note charges were not inflation-adjusted.

Across 1998–2014 there were 172,222 hospitalisations in the NIS identified with hallucinogen use disorder. The cohort was majority White (60%), predominantly male (67%), and 65% were aged 45 years or younger (Supplementary Table reported by the authors). From the start to the end of the study period (1998–2000 versus 2013–2014), national rates per 100,000 total NIS claims rose from 22.8 to 40.4, an increase of 1.8-fold. In-hospital mortality and markers of higher healthcare utilisation also increased over time. The in-hospital mortality rate rose from 0.3 to 0.6 per 100,000 NIS hospitalisations (a 2.3-fold increase), and the proportion of discharges to non-home destinations increased from 4.2 to 6.3 per 100,000 (a 1.5-fold increase). Median hospital length of stay was largely stable (2.0 days in early years versus 2.2 days in later years), but the median age of patients rose from 22 to 30 years and median hospital charges increased from $5,119 to $17,432 (these charges were not adjusted for inflation). Multivariable-adjusted analyses identified several characteristics associated with worse utilisation outcomes and/or higher in-hospital mortality. Older age, male sex, White race, a Deyo-Charlson index score of 2 or higher, insurance other than private payer, higher income, hospital region, urban hospital setting, and larger hospital bed size were each associated with more adverse utilisation patterns and/or greater in-hospital mortality. Exact odds ratios and confidence intervals were presented in the paper's tables (not reproduced in the extracted text).

Singh interpreted the findings as evidence that hospitalisations for hallucinogen use disorder and associated adverse inpatient outcomes increased substantially in the USA between 1998 and 2014. The rates of hospitalisation rose by about 1.8-fold over the study period, in-hospital mortality increased approximately 2.3-fold, non-home discharges rose about 1.5-fold, and unadjusted median hospital charges grew roughly 3.4-fold. The authors considered these results to expand understanding of the health-service burden attributable to hallucinogen use disorder. The paper notes that several patient-level and hospital-level factors were associated with worse outcomes, and highlights that some of these are potentially modifiable; the authors suggest these factors merit further investigation as targets for interventions or systems-level quality improvement. In the absence of similar national studies focused on hallucinogens, the authors compared their findings qualitatively to literature on opioid use disorder hospitalisations and observed some parallel factors associated with poor outcomes. Key limitations acknowledged by the investigators include the risk of misclassification inherent in using ICD-9-CM diagnostic codes, the inability to determine which specific hallucinogen (for example classical psychedelics, dissociatives, or entactogens) was implicated in each record, use of unadjusted hospital charges rather than costs, and the lack of out-of-hospital mortality data in the NIS. The authors note that misclassification might bias results toward the null and describe steps taken to improve diagnostic specificity. Finally, Singh suggested that policymakers could use these national data to guide resource allocation and that future research and programmes should aim to reduce the burden of hallucinogen use disorder hospitalisation and related mortality. The local Institutional Review Board approved the study and waived informed consent because the analysis used de-identified database records.