INTRODUCTION Attention deficit hyperactivity disorder (ADHD) is a prevalent neurodevelopmental disorder, affecting 2-7% of adults worldwide. Adults with ADHD experience heightened levels of stress and fatigue, and ADHD is likely to be an underlying factor in cases of exhaustion. Despite growing evidence on the assessment and treatment of adult ADHD, many patients remain underdiagnosed and undertreated, largely due to barriers such as lack of recognition, misunderstandings, and limited access to specialized care. Internet-delivered cognitive behavior therapy presents an opportunity for increasing access to psychological interventions, though the evidence for its efficacy remains underexplored for adult ADHD. METHODS A total of 240 participants will be recruited and randomly assigned to one of three conditions: Internet-based cognitive-behavioral stress-management (42%); Internet-based mindfulness stress-management (42%); or Wait-list control (16%). Participants in the intervention groups take part in twelve-module, twelve-week interventions with clinical support on demand. Outcome measures include self-reported quality of life (primary outcome measure), symptoms of ADHD, perceived stress, symptoms of exhaustion, depression, and anxiety. DISCUSSION The cognitive-behavioral stress- management intervention has shown promise in a previous single-arm open trial. In this study, we aim to further evaluate its efficacy by comparing it to an active mindfulness intervention and a wait-list control. This allows us to control for the expectation of benefit and common factors of internet interventions. Additionally, the inclusion of a wait-list control condition enables us to account for spontaneous improvement and regression toward the mean. Should the cognitive-behavioral intervention prove beneficial and efficacious, it could undergo further development and potentially be disseminated to a wider audience, either through routine healthcare or as a packaged product.