Prothixene is a thioxanthene derivative patented by Swiss multinational healthcare F. Hoffmann-La Roche & Co. as an antiemetic and neuroleptic agent. In preclinical models, prothixene shows patent antihistaminic activity. The central depressant activity of prothixene in the rotating rod test and the potentiation of thiopental narcosis and hypothermia in white mice (H strain) is one order lower than in the case of chlorprothixene. Prothixene has a higher protective effect in the supramaximal electric shock test with mice than promethazine and chlorprothixene. However, it has no effect on the reserpine ptosis in mice nor on the ulcerogenic action of reserpine in rats (Wistar strain). Its anti-serotonin activity is higher in vivo and in vitro than that of promethazine. The local irritation, tested on rabbits, is lower by 52% after prothixene application than after promethazine. Prothixene applied parenterally is more toxic to mice than promethazine. In oral administration, to mice, no differences in toxicity were found.