Role of Chronic Toxoplasmosis in Substance Abuse in Humans and Its Effect on Dopamine Levels

Abstract

Background: Toxoplasma gondii is a common parasitic infection agent that, in its chronic phase, forms persistent tissue cysts in neuronal cells, potentially leading to neurological and behavioral alterations. Aim: To investigate the role of chronic toxoplasmosis in human substance abuse and investigate its effect on dopamine levels, which is associated with substance abuse. Materials and Methods: The study was designed with a substance abuse group comprising 90 patients with substance addiction and a control group consisting of 75 individuals without substance addiction. The substance abuse group consisted of patients who were addicted to alcohol, cannabis, cocaine, heroin, or amphetamines. Anti-Toxoplasma gondii IgG and dopamine levels in the blood sera and anti-T. gondii immunoglobulin G (IgG) levels in the blood samples taken from the participants were analyzed via enzyme-linked immunosorbent assay. Results: T. gondii IgG was detected in 52 (57.8%) of 90 patients in the substance abuse group and 22 (29.3%) of 75 patients in the control group. There was a statistically significant relationship between T. gondii positivity and substance addiction (P = 0.001). However, no correlation was found between T. gondii positivity and the subgroups for the addiction type, criminal offense, imprisonment, or suicide attempt. Dopamine levels were statistically different between the groups. In the pairwise comparison of the groups, the dopamine levels in the T. gondii-positive substance abuse group were lower than in the other three groups, and this was statistically significant. Conclusion: In conclusion, the prevalence of T. gondii was higher in those with substance addiction than in those without. The fact that T. gondii alters dopamine levels was among the results. Since T. gondii can affect some behaviors of the host through changes in neurotransmitter levels, it was concluded that there is a significant relationship between T. gondii infection and substance abuse. © 2025 Elsevier B.V., All rights reserved.