BackgroundIn recent decades, stress-related disorders have received more attention, with an increasing prevalence, especially within the working population. The internet provides new options for broad dissemination, and a growing body of evidence suggests that web-based interventions for stress might be effective. However, few studies have examined the efficacy of interventions in clinical samples and work-related outcomes.ObjectiveThe aim of this study was to evaluate the efficacy of an internet-based cognitive behavioral intervention for stress-related disorders integrating work-related aspects (work-focused and internet-based cognitive behavioral therapy [W-iCBT]), compared with a generic internet-based cognitive behavioral therapy (iCBT) group and a waitlist control (WLC) group.MethodsIn this trial, 182 employees, mainly employed in the health care, IT, or educational sector, who fulfilled the criteria for a stress-related disorder, were randomized to a 10-week W-iCBT (n=61, 33.5%), generic iCBT (n=61, 33.5%), or WLC (n=60, 33%). Self-rated questionnaires on perceived stress, burnout, exhaustion, and other mental health– and work-related outcomes were administered before and after the treatment and at 6- and 12-month follow-ups.ResultsCompared with the WLC group, participants of the W-iCBT and iCBT groups showed an equal and significant reduction in the primary outcome (Shirom-Melamed Burnout Questionnaire [SMBQ]) from pretreatment to posttreatment assessment (Cohend=1.00 and 0.83, respectively) and at the 6-month follow-up (Cohend=0.74 and 0.74, respectively). Significant moderate-to-large effect sizes were also found in the secondary health- and work-related outcomes. The W-iCBT was the only group that exhibited significant effects on work ability and short-term sickness absence. Short-term sickness absence was 445 days lower than the WLC group and 324 days lower than the iCBT intervention group. However, no significant differences were found in terms of work experience or long-term sick leave.ConclusionsThe work-focused and generic iCBT interventions proved to be superior compared with the control condition in reducing chronic stress and several other mental health–related symptoms. Interestingly, effects on work ability and short-term sickness absence were only seen between the W-iCBT intervention and the WLC groups. These preliminary results are promising, indicating that treatments that include work aspects may have the potential to accelerate recovery and reduce short-term sickness absence because of stress-related disorders.Trial RegistrationClinicalTrials.gov NCT05240495; https://clinicaltrials.gov/ct2/show/NCT05240495 (retrospectively registered)