Although research has shown benefits of integrating psychological care in primary care settings, it is unclear how this form of treatment impacts individuals with comorbid substance use and depression. The findings are also mixed concerning how frequently this comorbid population seeks primary care services. This study examined the associations between substance use, depression, and medical treatment utilization among 224 primary care patients. The aim of the investigation was twofold. First, to determine if depression increases medical treatment utilization among patients with substance use disorders; second, to evaluate if behavioral health treatment reduces medical service utilization. A moderated mediation model with bootstrapping analyses revealed that depression strengthened the relationship between substance use and primary care treatment utilization (both medical and behavioral health). The model also indicated that behavioral health services were associated with fewer primary care visits for individuals with comorbid substance use and depression. Clinical and social implications are discussed.