Abstract
OBJECTIVES: This study investigated the influence of illness perceptions (IPs) on clinical severity across Major Depressive Disorder (MDD), Anorexia Nervosa (AN), Generalised Anxiety Disorder (GAD), Social Anxiety Disorder (SAD), and Panic Disorder (PD), and compared the IPs across these conditions. METHOD: We administered the Brief Illness Perception Questionnaire alongside disorder-specific severity scales to 774 participants (85.1% female). RESULTS: Significant associations between IPs and symptom severity emerged for AN and GAD only. Higher perceived Personal Control was associated with reduced severity in GAD but with greater severity in AN, whereas higher perceived Treatment Control was linked to lower severity in AN. In contrast, stronger perceptions of Concern were associated with increased severity in GAD. Although several IP dimensions demonstrated transdiagnostic overlap, differential associations also emerged, particularly for AN with respect to Timeline, Identity, and Emotional Representations. DISCUSSION: Our findings underscore the critical role of IPs in mental health severity and support the need for tailored recovery-oriented interventions targeting specific maladaptive IPs to improve clinical outcomes. However, given the high prevalence of comorbidity across the assessed disorders, the findings should be interpreted with caution, as overlapping conditions may have shaped both IPs and their associations with severity.