Methods This is a two-arm parallel single-blind randomised controlled trial comparing PES-EMDR+TAU to TAU including an internal pilot phase. Outcome data will be captured prior to randomisation, and at 4 (after PES), 8 (after EMDR) and 14 months postrandomisation by masked assessors. 144 adults with intellectual disabilities with a diagnosis of PTSD will be allocated (1:1) randomly using minimisation from National Health Service (NHS) community and inpatients services for adults with intellectual disabilities in England. Participants are eligible to take part in this trial if: (1) they are aged 18 or older, but younger than 66, (2) have a Full Scale IQ<75, (3) meet diagnostic criteria for PTSD and (4) have suffered a major identified trauma at least a year earlier and (5) are able to communicate using English and have capacity to consent to take part in this clinical trial. Participants allocated to the active intervention will receive 10 sessions of PES, followed by up to 15 sessions of EMDR alongside TAU. The active intervention is being delivered by psychologists experienced in working with adults with intellectual disabilities who have received additional intervention training. TAU is likely to include medication, behaviour support plans designed to target challenging behaviour, or non-trauma-focused psychological interventions. The primary outcome is a measure of PTSD symptoms. Secondary outcomes are other mental health problems, including anxiety and depression, challenging behaviour, participant and carer QoL, and carer burden. We are also capturing cost data to allow for a cost–utility analysis. A process evaluation will be completed using data generated from semistructured interviews with a sample of participants, therapists and carers alongside the capture of fidelity and adherence data.

Analysis The primary outcome will be assessed using an intention-to-treat analysis. Baseline characteristics will be compared between arms to determine whether any potentially influential imbalance occurred. The primary outcome will be analysed by analysis of covariance, adjusting for baseline values of the outcome and any variables used in the randomisation process. Secondary outcomes will be analysed using linear or logistic regression models as appropriate reflecting the distribution of the outcome variable. The treatment effect will be estimated as an adjusted difference between sample means, presented with 95% CIs and p values. A complier average causal effect analysis will be considered should the data availability be sufficient to estimate the impact of non-compliance. A series of subgroup analyses on the primary outcomes will be considered considering differences in the Impact of Event Scale–Intellectual Disabilities scores at 14 months for (1) differing levels of general intellectual functioning and (2) PTSD versus complex PTSD.

Ethics and dissemination This clinical trial was designed to allow for conclusions about whether PES/EMDR+TAU is efficacious in reducing symptoms of PTSD, relative to TAU, for adults with intellectual disabilities. A favourable ethical opinion has been received from an NHS ethics committee in the UK. The findings from this trial will be published within peer-reviewed journals and shared at national and international conferences. We will also aim to record and distribute podcasts detailing our findings together with our partners.

Trial registration number ISRCTN35167485.”