off a what? where abouts in the world are you, purity of cocaine varies accross the globe, through the years purity has been getting higher but still alot of cuts in cocaine. Levamisole is one that is known, not sure how it affects the high but heard it metabolises too aminorex which is a stimulant so expect more stimulation . ive had cocaine that didnt give me this jittery feelings and the high was awesome, i conclude its probably the cuts that make me jittery, though this is just pure hypothesis