Substance use disorders (SUDs) are a chronic disease that impacts the individual with a SUD as well as an entire family system. While family members of those with SUDs are one of the most important support networks in the recovery process, impacted family members have been found to experience more adverse health outcomes and altered functioning of the prefrontal cortex (PFC). These impacts negatively influence not only family members’ personal health but also the health of the family unit, which limits the family’s capability of providing its most effective support. Bowen’s conceptualization of differentiation of self can help explain the perspective of SUDs as a “family disease” and associated impacts on family members. Using functional near-infrared spectroscopy with a sample of 26 SUD-impacted family members, the present study examined associations between PFC activation in response to images of a loved-one seeking abstinence from a SUD and various components of differentiation of self (i.e., emotional cutoff, emotional reactivity, fusion with others, and I-position). Activation of the left dorsomedial PFC in response to SUD loved-one images associated negatively with emotional reactivity and positively with fusion with others. These findings did not replicate in a control group and have important implications for research and clinical practice.