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Background Reasoning may play a causal role in paranoid delusions in psychosis. SlowMo, a new digitally supported cognitive–behavioural therapy, targets reasoning to reduce paranoia. Objectives To examine the effectiveness of SlowMo therapy in reducing paranoia and in improving reasoning, quality of life and well-being, and to examine its mechanisms of action, moderators of effects and acceptability. Design A parallel-arm, assessor-blind, randomised controlled trial comparing SlowMo plus treatment as usual with treatment as usual alone. An online independent system randomised eligible participants (1 : 1) using randomly varying permuted blocks, stratified by site and paranoia severity. Setting Community mental health services in three NHS mental health trusts in England, plus patient identification centres. Participants A total of 362 participants with schizophrenia-spectrum psychosis. Eligibility criteria comprised distressing and persistent (≥ 3 months) paranoia. Interventions Eight face-to-face SlowMo sessions over 12 weeks plus treatment as usual, or treatment as usual alone (control group). Main outcome measures The primary outcome measure was paranoia measured by the Green Paranoid Thoughts Scale and its revised version, together with observer-rated measures of persecutory delusions (The Psychotic Symptom Rating Scales delusion scale and delusion items from the Scale for the Assessment of Positive Symptoms). The secondary outcome measures were reasoning (measures of belief flexibility, jumping to conclusions, and fast and slow thinking), well-being, quality of life, schemas, service use and worry. Results A total of 362 participants were recruited between 1 May 2017 and 14 May 2019: 181 in the SlowMo intervention group and 181 in the treatment-as-usual (control) group. One control participant subsequently withdrew. In total, 325 (90%) participants provided primary Green Paranoid Thoughts Scale outcome data at 12 weeks (SlowMo, n = 162; treatment as usual, n = 163). A total of 145 (80%) participants in the SlowMo group completed all eight therapy sessions. SlowMo was superior to treatment as usual in reducing paranoia on all three measures used: Green Paranoid Thoughts Scale total at 12 weeks (Cohen’s d = 0.30, 95% confidence interval 0.09 to 0.51; p = 0.005) and 24 weeks (Cohen’s d = 0.20, 95% confidence interval –0.02 to 0.40; p = 0.063); Psychotic Symptom Rating Scales delusions at 12 weeks (Cohen’s d = 0.47, 95% confidence interval 0.17 to 0.78; p = 0.002) and 24 weeks (Cohen’s d = 0.50, 95% confidence interval 0.20 to 0.80; p = 0.001); and Scale for the Assessment of Positive Symptoms persecutory delusions at 12 weeks (Cohen’s d = 0.43, 95% confidence interval 0.03 to 0.84; p = 0.035) and 24 weeks (Cohen’s d = 0.54, 95% confidence interval 0.14 to 0.94; p = 0.009). Reasoning (belief flexibility, possibility of being mistaken and Fast and Slow Thinking Questionnaire measure) improved, but jumping to conclusions did not improve. Worry, quality of life, well-being and self-concept also improved, improving most strongly at 24 weeks. Baseline characteristics did not moderate treatment effects. Changes in belief flexibility and worry mediated changes in paranoia. Peer researcher-led qualitative interviews confirmed positive experiences of the therapy and technology. Nineteen participants in the SlowMo group and 21 participants in the treatment-as-usual group reported 54 adverse events (51 serious events, no deaths). Limitations The trial included treatment as usual as the comparator and, thus, the trial design did not control for the effects of time with a therapist. Conclusions To the best of our knowledge, this is the largest trial of a psychological therapy for paranoia in people with psychosis and the first trial using a brief targeted digitally supported therapy. High rates of therapy uptake demonstrated acceptability. It was effective for paranoia, comparable to longer therapy, and equally effective for people with different levels of negative symptoms and working memory. Mediators were improvements in belief flexibility and worry. Our results suggest that targeting reasoning helps paranoia. Future work Further examination of SlowMo mechanisms of action and implementation. Trial registration Current Controlled Trials ISRCTN32448671. Funding This project was funded by the Efficacy and Mechanism Evaluation (EME) programme, a MRC and National Institute for Health Research (NIHR) partnership. This will be published in full in Efficacy and Mechanism Evaluation; Vol. 8, No. 11. See the NIHR Journals Library website for further project information.

Original publication




Journal article


Efficacy and Mechanism Evaluation


National Institute for Health Research

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