ABSTRACT Objective To compare the ratio of the right and left second and fourth digits (2D:4D), aggression, and impulsivity levels in opiate use disorder (OUD), alcohol use disorder (AUD), and healthy controls. Methods Eighty-four patients diagnosed with OUD, 58 patients diagnosed with AUD, and 58 healthy volunteers were included. Participants administered the sociodemographic data form, Barratt Impulsivity Scale (BIS-11), and Buss-Perry Aggression Questionnaire (BPAQ). Results Healthy controls’ right-hand 2D:4D ratio was higher than the OUD and AUD groups (respectively; p < .001, p < .001). The right-hand 2D:4D ratio was similar between OUD and AUD (p = .542). Left-hand 2D:4D ratio of healthy controls was higher than OUD and AUD groups (respectively; p < .001, p < .001). The left-hand 2D:4D ratio was similar between OUD and AUD (p = .429). The BIS-11 scores of the healthy controls were lower than OUD and AUD groups (respectively; p < .001, p < .001). It was found similar in the AUD and OUD groups (p = .264). The BPAQ scores of the healthy controls were lower than the OUD group and the AUD group (respectively; p < .001, p < .001). It was found similar in the AUD and OUD groups (p = .973). Conclusion It was found that the 2D:4D ratio of both hands in OUD and AUD patients is lower than that of healthy volunteers. The 2D:4D ratio can be an indicator of addiction, regardless of the type of substance used.