Clinical Characteristics of Patients With Overdose Engaging in Nonmedical Use of Prescription Drugs: A Single‐Center Study in Japan

ABSTRACT Introduction The nonmedical use of prescription drugs (NMUPD) through channels outside the healthcare system has emerged as a significant public health issue; however, its clinical implications in overdose cases remain underexplored in Japan. This study aimed to elucidate the prevalence and characteristics of NMUPD in patients with acute drug overdose. Methods In this observational study, we retrospectively studied patients with overdose who were admitted to a tertiary emergency department in Japan between April 2017 and March 2024. Patients were categorized into the NMUPD group (obtained drugs via nonmedical routes, such as family, acquaintances, the Internet, and unauthorized workplace access) and prescribed group. Demographic, clinical, and overdose‐related variables were compared between the groups. Statistical analyses included the chi‐square and Mann–Whitney U tests, with multiple imputation for missing data. Results Among the 416 patients with overdose, 7.9% met the NMUPD criteria. The primary sources of NMUPD were family members, followed by friends/acquaintances, Internet purchases, and unauthorized pharmacy access. The NMUPD group showed significantly higher rates of alcohol coingestion ( p = 0.029) and absence of psychiatric diagnoses ( p = 0.009). Benzodiazepines predominated in both groups, with frequent use of non‐benzodiazepine and antidepressants. Conclusions This study revealed that NMUPD occurs even within Japan's tightly regulated healthcare system, primarily via informal sources such as patients' families and friends. NMUPD was linked to alcohol coingestion and limited psychiatric follow‐ups. NMUPD involved several commonly prescribed psychotropic drug classes rather than a single class.