The thermal decomposition of [RuCl2(η6-p-cymene)]2 (1) and its biologically active N-alkylphenothiazine compounds of composition L[RuCl3(η6-p-cymene)] where L = CPH+ (2), TFH+·HCl (3), and TRH+ (4) (chlorpromazine hydrochloride, CP·HCl; trifluoperazine dihydrochloride, TF·2HCl; and thioridazine hydrochloride, TR·HCl, respectively) has been studied. The crystal and molecular structure of compound 3 was determined earlier by single crystal X-ray diffraction analysis. The thermal data were collected by simultaneous TG/DSC measurements. For evolved gas detection, the qualitative reaction of chlorides with AgNO3 in an acidic solution was applied. The measurements were carried out in the temperature range to 700 °C in nitrogen atmosphere. Compounds of L[RuCl3(η6-p-cymene)] crystallize with water or water/2-propanole. On the basis of thermal data, the trend in the solvent bonding energies was assessed.