Clastogenic effect of the psychotropic drug thioridazine on human chromosomes in vivo.

Thioridazine (Mellaril), a psychotropic drug belonging to the phenothiazine group of drugs, was evaluated for its in vivo clastogenic effect on human chromosomes in lymphocyte cultures. Lymphocyte cultures were set up with peripheral blood samples of psychiatric patients (diagnosis: schizophrenia, mania, manic depressive psychosis, acute psychotic episode) who were on therapeutic doses of thioridazine for over 4 weeks. Two sets of controls were used: (1) newly diagnosed psychiatric cases (same type as above) who were not yet under therapy and (2) healthy individuals from the general population. The chromosomal aberration frequency was found to be significantly increased in the patients exposed to this drug as compared to the two sets of controls. The results point to a clastogenic and mutagenic potential of thioridazine and warrent a more careful consideration of its use in medicine.