Nicotine changes how your brain and your body function. The net results are somewhat of a paradox: Nicotine can both invigorate and relax. Nicotine initially causes a rapid release of adrenaline, the "fight-or-flight" hormone. If you've ever jumped in fright at a scary movie or rushed around the office trying to finish a project by your deadline, you may be familiar with adrenaline's effects: rapid heartbeat, increased blood pressure and shallow breathing – this will quickly mellow as the nicotine dose wears off. The nicotine dose brings the initial onset of an actual cigarette without the harmful side effects.