Nicotine is one of the most addictive drugs, and smoking increases the risk of cancer. Cigarettes contain over 4,000 chemicals including nicotine, ammonia, acetone, arsenic and carbon monoxide. Smoking causes permanent changes in the brain and 80% of ex-smokers will return to smoking within a month of having one cigarette. Tobacco use is linked to many adverse health effects like heart disease, lung cancer, and emphysema and is the leading cause of preventable death. Most smokers become addicted before age 18 and it is difficult to quit once addicted.