The effect of cathinone and N-formylnorephedrine, two psychoactive amines of khat (Catha edulis Forsk.) and their enantiomers have been studied on plasma levels of triiodothyronine (T3) and thyroxine (T4) in male Wistar rats. The rats were injected with 5, 10 and 30 mg/kg. body weight of four khatamines and the blood samples were collected 2 h after administration. In the separate set of experiments the effect of these khatamines at 1, 2 and 4 h after their administration was also examined. All khatamines failed to produce a significant dose dependent increase in T3 and T4 levels in the dose of 5 mg/kg. However, all these compounds produced a significant dose dependent increase in T3 and T4 levels at higher doses but only T4 levels were increased following the dose of 10 mg/kg. Our studies on the effect of khatamines in T3 and T4 levels at various time showed a significant increase in T4 levels in all the four groups treated with various khatamines and the peak effect was observed in 2 h in case of (-)- and (+)-cathinone and 4 h in case of (-) and (+)N-formylnorephedrine. This study suggests that the symptoms observed in khat chewers including hyperthermia, anorexia, and metabolic changes may to some extent be attributed to the thyroid stimulating effect of khatamines. However, further studies are needed to establish the mechanism of release of thyroid hormones by these compounds and their involvement in the pharmacological effects.