BackgroundiSupport is an online program developed by the World Health Organization to provide education, skills training, and social support to informal carers of persons with dementia. This pilot study examines the feasibility of the protocol for a main effectiveness trial of iSupport-Portugal and explores how the intervention and control arms compare over time on well-being outcomes.MethodsA mixed-methods experimental parallel between-group design with two arms is followed. Participants were recruited nationwide, by referral or advertising, through the National Alzheimer’s Association. Inclusion criteria are being Portuguese adults, providing e-consent, providing unpaid care to someone with dementia for at least 6 months, experiencing relevant scores on burden (≥ 21 on ZBI) or depression or anxiety (≥ 8 on HADS), and using webpages autonomously. Participants were consecutively randomized to receive iSupport-Portugal or an education-only e-book and were not blinded to group assignment. Data were collected online with self-administered instruments, at baseline, 3 and 6 months after. Outcomes comprise caregiver burden, depression, anxiety, QoL, positive aspects of caregiving, and self-efficacy. Generalized estimating equations were used to estimate group, time, and group-by-time effects. Intervention engagement data were extracted from iSupport’s platform. Semi-structured interviews were conducted.ResultsForty-two participants were allocated to the intervention (N = 21) and control (N = 21) arms. Participation (78.1%) and retention rates (73.8%) were fair. More carers in the control arm completed the study (N = 20, 95.2%) than in the intervention arm (N = 11; 52.4%) (χ2 = 9.98, p = .002). Non-completers were younger, spent less time caring, and scored higher on anxiety. Among carers in the intervention arm, the average attendance rate was of 53.7%. At post-test 38.9% of participants still used iSupport; the remainder participants interrupted use within 2 weeks (Mdn). For per-protocol analyses, significant group-by-time interaction effects favouring the intervention were found for anxiety (Wald χ2 = 6.17, p = .046) and for environmental QoL (Wald χ2 = 7.06, p = .029). Those effects were not observed in intention-to-treat analyses adjusted for age. Interviewees from the intervention arm (N = 12) reported positive results of iSupport on knowledge and on experiencing positive feelings. No adverse effects were reported.ConclusionsThis study provides information for a forthcoming full-scale effectiveness trial, as on the acceptability and potential results of iSupport-Portugal. iSupport is suggested as a relevant resource for Portuguese carers.Trial registrationClinicalTrials.gov, NCT04104568. 26/09/2019.