Objective To explore the potential efficacy of multi-modular motion-assisted memory desensitization and reprocessing (3MDR) in British military veterans with treatment-resistant service-related... Show moreObjective To explore the potential efficacy of multi-modular motion-assisted memory desensitization and reprocessing (3MDR) in British military veterans with treatment-resistant service-related PTSD. Methods Exploratory single-blind, randomized, parallel arm, cross-over controlled trial with nested process evaluation to assess fidelity, adherence and factors that influence outcome. Results A total of 42 participants (all male) were randomized with 83% retention at 12 weeks and 86% at 26 weeks. The difference in mean Clinician-Administered PTSD Scale for DSM-5 scores between the immediate and delayed 3MDR arms was -9.38 (95% CI -17.33 to -1.44,P = 0.021) at 12 weeks and -3.59 (-14.39 to 7.20,P = 0.513) at 26 weeks when both groups had received 3MDR. The likely effect size of 3MDR was found to be 0.65. Improvements were maintained at 26-week follow-up. 3MDR was found to be acceptable to most, but not all, participants. Several factors that may impact efficacy and acceptability of 3MDR were identified. Conclusion 3MDR is a promising new intervention for treatment-resistant PTSD with emerging evidence of effect. Show less