Eating disorders and subsequent risk of substance use disorders involving illicit drugs: a Danish nationwide register-based cohort study

Purpose: No study has investigated the ongoing risk of substance use disorders involving illicit drugs (ISUD) after first eating disorder (ED) and whether the pattern of risk differs according to types of ED and ISUD. Therefore, we aimed to longitudinally assess the risk of a subsequent diagnosis of any ISUD (pooled category) and specific ISUD after a first-time diagnosis of anorexia nervosa (AN), bulimia nervosa (BN), or unspecified ED (USED). Methods: A retrospective cohort study using data from Danish nationwide registers identified 20,759 ED patients and 83,038 matched controls (1:4 ratio). Risk of any ISUD diagnosis after first ED diagnosis was estimated by generating hazard ratios (HR). Logistic regression was applied to assess associations between each ED and specific ISUD. Results: Patients with AN, BN, and USED (without a prior ISUD diagnosis) exhibited an increased relative risk of a subsequent diagnosis of any ISUD compared with respective controls, and the elevated risk persisted over 10 years (AN, adjusted HRs ranging from 1.60 [99% CI 1.15–2.24] to 5.16 [3.14–8.47]; BN, 2.35 [1.46–3.79] to 14.24 [6.88–29.47]; USED, 2.86 [1.35–3.79] to 8.56 [3.31–29.47]). The highest estimates were observed during the first year of follow-up. Each ED type was associated with an increased likelihood of all types of ISUD. AN and USED were most strongly associated with sedatives/hypnotics, BN with other illegal substances (e.g., ecstasy and hallucinogens). Conclusions: ED patients have a considerable risk for subsequent ISUD. Prevention efforts and treatment targeting ISUD are likely required to improve ED treatment prognosis.