Although job stress models suggest that changing the work social environment to increase job resources improves psychological health, many intervention studies have weak designs and overlook influences of family caregiving demands. We tested the effects of an organizational intervention designed to increase supervisor social support for work and nonwork roles, and job control in a results-oriented work environment on the stress and psychological distress of health care employees who care for the elderly, while simultaneously considering their own family caregiving responsibilities. Using a group-randomized organizational field trial with an intent-to-treat design, 420 caregivers in 15 intervention extended-care nursing facilities were compared with 511 caregivers in 15 control facilities at 4 measurement times: preintervention and 6, 12, and 18 months. There were no main intervention effects showing improvements in stress and psychological distress when comparing intervention with control sites. Moderation analyses indicate that the intervention was more effective in reducing stress and psychological distress for caregivers who were also caring for other family members off the job (those with elders and those "sandwiched" with both child and elder caregiving responsibilities) compared with employees without caregiving demands. These findings extend previous studies by showing that the effect of organizational interventions designed to increase job resources to improve psychological health varies according to differences in nonwork caregiving demands. This research suggests that caregivers, especially those with "double-duty" elder caregiving at home and work and "triple-duty" responsibilities, including child care, may benefit from interventions designed to increase work-nonwork social support and job control. (PsycINFO Database Record (c) 2019 APA, all rights reserved).