Substances that underlie a diagnosis of multiple drug use disorder: a 2021-2024 Swedish cohort study

Abstract Background Multiple drug addiction is a public health problem. An understanding of the substances involved is a prerequisite for treatment, public policy, and interventions. Although multiple drug use disorder (MDUD) is a common diagnosis, the substances underlying it remain unclear. This study investigated the substances that lie behind this diagnosis. Methods The study used Region Stockholm data on diagnoses (ICD-10 codes) and self-reported substance use from the Swedish National Addiction Care Quality Register. Patients diagnosed with ≥1 substance use disorder (SUD) (codes F10-F16, F18-F19) who reported using ≥1 substance were divided into 1) MDUD only (n = 988), 2) MDUD + ≥1 other SUD (n = 5054), 3) ≥2 other SUDs (n = 2310), and 4) 1 other SUD (n = 17483). Number and share of patient characteristics and frequency and share of substance pairs were calculated. Heat maps comparing reported and diagnosed substance use were created. Results The MDUD only group was the youngest (79% <40 years) and the only group where more (60%) reported cannabis than alcohol (56%) use. The 1 other SUD group was oldest and primarily diagnosed with alcohol use disorder only (81%). Alcohol and cannabis featured most prominently in combinations reported by many patients (e.g., cannabis: 3 combinations in > 20% with MDUD only). Sedatives/hypnotics, other stimulants, and cocaine also featured in multiple combinations. Correspondence between self-report and diagnosis was >60% for alcohol and opioids in all groups and for cannabis in two. Correspondence was <50% for several disorders and groups (e.g., cocaine: 1 other SUD, 27%). Patients typically reported using the substances that corresponded with their diagnoses (e.g., 81%-91% for cannabis and cocaine). Conclusions Alcohol, cannabis, sedatives/hypnotics, other stimulants, and cocaine likely underlie many MDUD diagnoses. The findings suggest that SUDs are underdiagnosed in those with only an MDUD diagnosis and in the other groups in the study. Key messages • Multiple drug use disorder (ICD-10 code F19) is sometimes used instead of substance-specific diagnoses that are important for treatment, public policy, and interventions. • The findings suggest that substances and substance combinations underlying multiple drug use disorder typically include alcohol, cannabis, sedatives/hypnotics, other stimulants, and cocaine.