Relationship between toxoplasmosis and addiction: A systematic review and meta-analysis

Chronic toxoplasmosis has been associated with behavioral alterations in both humans and animal models. Given that substance addiction involves behavioral and neurochemical changes, this study aimed to investigate the potential association between Toxoplasma gondii (T. gondii) infection and substance use disorders by synthesizing available evidence through a meta-analysis. A systematic search of five databases was conducted using relevant keywords to identify English-language articles published up to January 19, 2025. Studies were screened according to predefined inclusion and exclusion criteria. A random-effects model was applied to calculate the pooled odds ratio (OR) and corresponding p-value. A total of 18 studies were included in the systematic review, of which 9 met the criteria for inclusion in the meta-analysis, encompassing 2499 participants (1018 individuals with substance use disorders and 1481 controls). The random-effects model estimated an OR of 1.86 (95 % CI: 1.25-2.76) for anti-T. gondii IgG antibodies among individuals with substance use disorders compared with controls. Egger's test indicated no publication bias. Sensitivity analysis confirmed the robustness and stability of the observed association between anti-T. gondii IgG seropositivity and addiction. These findings demonstrate a statistically significant association between T. gondii infection and substance use disorders. However, the limited number of available studies highlights the need for further epidemiological investigations, particularly longitudinal studies, to clarify the nature and direction of this relationship.