Understanding and treating persecutory delusions: an interventionist-causal model approach

Around one in ten people regularly experience suspicious thoughts that someone intends to harm them, and for some this escalates into full persecutory delusions that wreck their lives. Current treatments for paranoia are limited. The standard approach—cognitive behavioural therapy—helps many people with anxiety disorders, but has not been as effective for paranoia. This research programme aims to change that by treating paranoia the way psychologists now treat phobias: by systematically testing which factors actually cause the problem, then building treatments that directly target those causes. The researchers will run four linked studies. They will deliberately increase or decrease suspected causal factors—such as threat beliefs or social avoidance—and measure the effect on paranoia. One study will use virtual reality social environments, which allow precise control over social situations that trigger suspicious thoughts. Another will examine how cannabis use, the most common illicit substance, influences paranoia. If the approach works, it could produce a new treatment package for persecutory delusions that is more effective than current options. The work also has a fundamental science component: it will clarify which psychological mechanisms actually cause paranoia, rather than merely correlate with it. That causal knowledge could inform future treatments for the 10–20% of the general population who experience milder suspicious thoughts.