Delusions — fixed, false beliefs that cannot be changed by evidence — are a key symptom of many psychotic disorders. Diagnostic manuals like the DSM-5 group them into broad categories, with recurring themes including being persecuted or harmed, delusions of grandeur, or unusual bodily sensations. Yet little research has actually explored the limitations of these categories, whether they are universally relevant, or if they vary by culture.
    
A new study in Schizophrenia Bulletin, led by University College London's Elisavet Pappa, explores these categories in greater depth. Analysing 155 studies, altogether encompassing 173,920 participants, the team identifies 37 distinct delusional themes — far more than those previously accounted for. Their findings also reveal significant cultural variations in how people experience delusion, highlighting the need for a broader, more globally informed approach to psychosis.
    
The team drew insights from research involving adults aged between 18 and 65 from around the world, all of whom had psychotic disorders. From these studies, they examined how common different delusional themes were, while also gathering demographic information, diagnostic details, assessment methods, and data on medication use.

Their analysis uncovered a much broader range of delusions than those typically found in diagnostic manuals, along with notable cultural differences. Established assessment scales identified 21 themes, but incorporating additional classifications expanded this to 37, introducing categories such as hypochondria, terror of global catastrophe, and fear of poisoning. As lead author Elisavet Pappa told Research Digest, this reveals a "much broader range of delusions and stronger cultural influences" than previously recognised.

One key finding was a 'social gradient' in delusions: people were far more likely to experience delusions about those close to them, such as family members, than more distant figures like neighbours or the police. This has important implications for risk assessment, as delusions about specific individuals can sometimes be linked to harmful or aggressive behavior (though the team does point out the risk of violence from those in psychosis remains low). It also highlights what Pappa describes as "the fundamental role of interpersonal relationships in shaping delusional content, regardless of cultural background or delusional theme."

The study also found interesting links between certain delusional themes and psychiatric diagnoses. While some patterns aligned with traditional classifications, such as grandiose delusions in bipolar disorder, others challenged existing assumptions. For example, delusions of jealousy, which are typically associated with delusional disorder, were also found to be common in schizophrenia and bipolar disorder.

Compared to countries in the 'Anglo' cultural cluster, such as the UK and US, Southern Asia showed a higher prevalence of jealousy delusions, Eastern Europe more guilt/sin delusions, and the Middle East higher rates of sexual and jealousy delusions. These findings seem to suggest that cultural context, such as the influence of different religions or normative social standards, plays a major role in shaping delusions. This only reinforces the importance of looking beyond WEIRD perspectives and adopting a more worldwide and culturally conscious outlook when exploring delusions.

Taken together, the study's findings highlight a wider and more complex landscape of delusions than previously recognised — one that extends beyond current, potentially too narrow, diagnostic frameworks.

Ultimately, Pappa says, it highlights "the need to move beyond rigid diagnostic frameworks toward a more nuanced, individualized, and culturally informed approach to psychosis. […] By broadening the understanding of delusional themes, clinicians can develop more effective diagnostic tools, improve therapeutic interventions, and enhance patient outcomes."

Read the paper in full:
Pappa, E., Baah, F., Lynch, J., Shiel, L., Blackman, G., Nichola Raihani, & Bell, V. (2025). Delusional Themes are More Varied Than Previously Assumed: A Comprehensive Systematic Review and Meta-Analysis. Schizophrenia Bulletin. https://doi.org/10.1093/schbul/sbae225

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