Heavy drinking in relationships is complex and we focus on an understudied sample of concerned partners (CPs) worried about their U.S. service member/veteran partner's drinking. We evaluated the link between CP drinking and their own mental health, and how CP drinking moderated the efficacy of a web‐based intervention designed to address CPs' mental health and communication. CPs (N = 234) were randomly assigned to intervention or control and completed assessments at baseline and 5 months later. CP drinking was associated with greater CP depression, anxiety, and anger independent of partner drinking. Moreover, the intervention was more efficacious in reducing depression for heavy drinking CPs. CPs are often an overlooked population and resources to help support them are needed.