Nicotine is a highly addictive stimulant found in tobacco that is quickly absorbed into the bloodstream when smoked.

What It Does:

Nicotine is as addictive as heroin or cocaine, which makes it extremely difficult to quit. Those who start smoking before the age of 21 have the hardest time breaking the habit.

Physical effects of nicotine use include rapid heartbeat, increased blood pressure, shortness of breath, and a greater likelihood of colds and flu.

Users have an increased risk for lung diseases like lung cancer, heart disease, and stroke. They may have bad breath and yellowed teeth, and are more likely to get cancers of the mouth and neck.

Withdrawal symptoms of nicotine include anxiety, anger, restlessness, and insomnia.