Essentially, nicotine taps into your brain’s reward pathways and starts to release dopamine and serotonin within about 10 to 20 seconds of your first inhale, giving you the “pleasure” response associated with smoking very rapidly. (“If it took a couple of hours for that dopamine release, people probably wouldn’t get addicted,” says Professor Shahab.) At the same time, nicotine “unlocks” your adrenal glands, pouring epinephrine (adrenaline) and norepinephrine (another hormone vital for the “fight-or-flight” stress response) into your bloodstream and giving you a brief buzz. Nicotine levels in the blood peak after about 20 minutes, and then it’s all downhill.