Clinical Characteristics of Over‐The‐Counter Drug Misusers in Psychiatric Practice in Japan: Comparison Between Codeine Misusers and Dextromethorphan Misusers

PURPOSE: In recent years, the misuse of over-the-counter (OTC) medications has been increasing in psychiatric clinical settings in Japan. This study aimed to compare individuals who misuse codeine (COD) with those who misuse dextromethorphan (DXM) to clarify the clinical characteristics of DXM misusers and to consider the support measures needed for this population. METHODS: We used data from the 2024 National Survey on Drug-Related Disorders in Psychiatric Inpatient Facilities. Individuals who primarily misused OTC containing COD (COD group) and DXM (DXM group) were extracted from the database. We examined demographic characteristics, ICD-10 subcategories, and comorbid psychiatric disorders and compared the two groups using Fisher's exact test. Factors associated with DXM misuse were further analyzed using multivariable logistic regression. RESULTS: The study included 160 individuals in the COD group and 72 in the DXM group. Compared with the COD group, the DXM group had higher proportions of females and younger individuals, as well as higher rates of drug use within the past year and a history of self-harm or suicide attempts. The DXM group also showed significantly higher comorbidity rates of "acute intoxication" and "mood disorders (F3)" based on ICD-10. In the multivariable logistic regression analysis, younger age (AOR = 2.558, 95% CI: 1.218-5.371), acute intoxication (AOR = 2.73, 95% CI: 1.254-5.942), and comorbid mood disorders (AOR = 2.201, 95% CI: 1.146-4.227) were significantly associated with DXM misuse. CONCLUSION: These findings highlight the importance of acute-phase management, assessment of comorbid psychiatric disorders, and interventions that include suicide-risk evaluation in supporting individuals who misuse DXM. Furthermore, preventive education incorporating perspectives on mental-health-focused suicide prevention, as well as regulatory measures for OTC medication sales, are urgently needed.