What causes a muscle to twitch in your leg?

Many reasons: Drug overdose (caffeine, amphetamines drug side effect (such as from diuretics corticosteroids or estrogeexercise lack of nutrients in the diet stress twitches not caused by disease or disorders (benign twitches) often affecting the eyelids calf, or thumb normal and quite common often triggered by stress or anxiety come and go and donot last for more than a few days symptoms of a nervous system.