Aims: Research over many years indicates that individuals with problematic alcohol or drug use or gambling disorders can cause considerable burden on family members. And yet, affected family members (AFMs) are largely neglected in research, health and social care policy and provision. To address the needs of AFMs of people struggling with a substance use or gambling disorder, the 5-Step Method was developed. Methods: The goal of this study is to evaluate the routinely delivered 5-Step Method in the Netherlands using measures at baseline (N = 145), and end-of-treatment (N = 102). In addition, a subsample at three-month post intervention (N = 70) was included. The intervention was delivered via video-conferencing to half (47.6%) of the participants. Findings: Participants reported significantly lower rates of Total Family Burden after completing the 5-Step Method, when comparing measurements at baseline and end-of-treatment (d = 0.56), and measurements at baseline and three-month post intervention (d = 0.85). In addition, participants following the intervention via video-conferencing (N = 69) performed equally well or better compared to participants following the intervention face-to-face (N = 76). Conclusions: Following the 5-Step Method for AFMs results in lower Total Family Burden. In accordance with the Stress-Strain-Information-Coping-Support (SSICS) model, the effectiveness of the intervention could be improved by finding new ways of increasing support for AFMs.