Adolescent substance abuse is a common problem and family interventions are emerging as a strategy to prevent it and assist family coping. The effectiveness of a prevention-focussed family intervention was evaluated for its secondary impacts on improving parental mental health and family functioning. Twenty-four secondary schools in Melbourne Victoria were randomly assigned to either a control condition or an intervention titled Resilient Families. The two intervention levels analysed were: (1) a parenting booklet only and; (2) combining the booklet with face-to-face parent education sessions. Parent surveys at baseline were followed up one year and four years later. Repeated-measures analysis (n = 560) found parents attending parent education demonstrated reductions in mental health symptoms, however this had negative effects on family cohesion and no impact on family conflict. These findings were interpreted in terms of parent education assisting parent mental health by promoting assertive parenting styles that may increase adolescent-parent tension by encouraging firmer parental boundaries and strategies to reduce adolescent substance use.