Tolerance develops to sympathetic effects of khat in humans.

Khat chewing has been found to induce, like amphetamines, psychostimulation and increase in sympathetic tone. The possibility that tolerance develops to these effects has been studied by comparing the influence of the chewing of a standard dose of khat on some physiological parameters in chronic consumers and naive subjects. Systolic blood pressure appears to rise in both groups, but the increase in diastolic pressure was more marked in naive subjects and inversely related to the reduction of pulse rate. The increases of respiratory rate and body temperature were also higher in naive subjects. In both groups, all these effects disappeared after 18 h. These results are consistent with an amphetamine-like mechanism of action and suggest that tolerance develops to the sympathetic effects of khat.