Schizophrenia affects 0.8% of the UK population, usually starts in early adult life and leads to persistent disability in most cases . It carries a high risk of suicide (8%) and deliberate self-harm  and, on a population basis, people with schizophrenia are more likely to perpetrate acts of aggression than their peers . While drug treatment has improved, approaching fifty per cent will continue to experience treatment resistant symptoms  or symptoms arising from refusal to adhere with drug regimes . Auditory hallucinations rank among the most prominent of the treatment resistant symptoms  and the most distressing and high risk of all are command hallucinations [6, 7]. Command hallucinations are very prevalent in people who experience schizophrenia. A recent review by Shawyer et al  reported a median prevalence rate of 53% with a wide range from 18% to 89% in a sample of adult psychiatric patients. Furthermore, it was reported that 48% of command hallucinations stipulate harmful or dangerous actions  rising to 69% among patients in medium secure units . This rate was significantly higher in the forensic population with 83% of voice hearers experiencing command hallucinations with criminal content .
However, the link between command hallucinations and harm to self or others is not straightforward. In the Macarthur study [9, 10] no association was reported between the presence of delusions or command hallucinations and violence (GBH, assault and threats with a weapon). Thoughts about violence, on the other hand, were a strong predictor of violence six months later. A recent secondary analysis of the Macarthur study by Rogers [11, 12] found that an additional significant predictor of aggression is beliefs about having to "obey" the voice. Thus, it appears to be the content of the individual's thinking and how this reflects the dynamics of the individual's relationship with their supposed persecutor who is commanding that is found to be predictive of harm to self and others in command hallucinations [13, 14]. This was further confirmed by Trower et al  who found that it is the content of the voice and the individual's relationship with the personified voice that predicts compliance, distress and depression. These findings are in accordance with the social rank theory which suggests that individuals in subordinate positions will comply with the demands of those more dominant, or appease when compliance is risky or dangerous, but escape is impossible. In command hallucinations, the greater the power differential between the voice and the voice hearer, the greater the possibility of complying with "benevolent" voices or resisting but appeasing "malevolent" voices [13, 14]. From the voice hearer's point of view, non-compliance risks harmful action from the voice (e.g. death to self or family), placing the individual in a dilemma often resolved by harmful appeasement or compliance. These findings have been independently replicated by Fox et al  comparing people who have complied with their voices vs. those who have resisted compliance. The former perceived their commanding voice to be more powerful and themselves to be inferior, hence motivating the need to submit to the voice and comply with its commands.
Nevertheless, predicting who, and when individuals will act on their voices has proven difficult in spite of these epidemiological data; also, why people respond to their voices in the above varying ways (e.g. complying, appeasing) is something that warrants exploring. The aim of our MRC COMMAND trial is to answer these questions while at the same time evaluate the efficacy of a cognitive behavioural therapy (CTCH) in reducing harmful compliance with command hallucinations. Cognitive behavioural therapy (CBT) is a psychological therapy originally developed for the management of emotional disorders like depression and anxiety disorders. The link between thinking and emotion/behaviour lies at the heart of this therapy such that emotional and behavioural responses are principally influenced by cognitive appraisals. CBT was further developed for the treatment of severe mental health problems like psychosis and has been thoroughly validated through large-scale pragmatic trials using primarily standard psychosis outcomes (e.g. Positive and Negative Symptom Scale)  (Birchwood & Trower, 2006). CBT is now recommended by the National Institute for Clinical Excellence  (2002) "to reduce psychotic symptoms, increase insight and promote medication adherence".
The primary hypothesis to be tested is whether in patients with command hallucinations who have acted on their voices and are therefore at high risk of doing so again, cognitive therapy for command hallucinations (CTCH) will prevent further harmful compliance behaviour, and thereby reduce risk.
Secondary hypotheses predict that:
(a) any reduction in compliance will be mediated by reduced conviction in the perceived power of the persecuting voice,
(b) CTCH will reduce delusional distress and depression, but
(c) we are not predicting any change in the frequency or topography of voices per se.