any drink like kick, relentless, red bull etc... contains caffeine
caffeine is a stimulant found in tea, coffee, stimulation drinks, coca cola (unless caffeine free). caffeine affects heart rate
, production of adrenalin, blood pressure, release of hormones such as serotonin etc..
caffeine is an alkaloid like nicotine
and like nicotine (found in tobacco products) can be addictive although not to the same degree as nicotine