Hyperthyroidism State Linked to Broader Dark Personality Profile, New Study Finds

A study in Current Psychology finds that hyperthyroidism is associated with higher scores on the Dark Tetrad (Machiavellianism, psychopathy, and sadism; narcissism elevated compared with hypothyroidism but not different from controls) versus hypothyroidism and healthy controls. Using the Short Dark Tetrad (SD4) with 154 adults (49 hyperthyroid, 52 hypothyroid, 53 controls), hyperthyroid participants showed higher scores on multiple dark traits even after adjusting for age and sex. The authors caution the effects are modest, based on self-reported diagnoses in a cross-sectional design, reflecting group-level associations rather than individual dispositions, and they advocate longitudinal studies with objective hormone data to clarify mechanisms such as CNS hyperarousal from excess thyroid hormones.