Tobacco also contains over 300 other chemicals including lead, formaldehyde, radioactive particles and cancer-causing agents. Tobacco smoke produces arsenic, hydrogen cyanide, ammonia, acetone and carbon dioxide, the last of which interferes with the body's ability to carry oxygen. The U.S. Environmental Protection Agency classifies cigarette smoke as an environmental hazard. Tolerance to a drug is the body's increasing resistance to the chemical's effects. This means that one's body requires larger amounts of a drug to have the same effects that lower doses used to create.
Most stimulants rapidly produce a high tolerance.
Physical dependence to a drug occurs when an individual's tissue cells get used to a certain level of intoxication. This means the body physically changes, needing the drug in regular doses to maintain its chemical balance. Psychological dependence to a drug occurs when a person needs regular doses of the drug to maintain mental and emotional stability. In either case, a drug dependent person will experience some form of withdrawal symptoms when drug use is discontinued. Physical effects of smoking include irritation of the lung tissues, constricted blood vessels, pupil dilation and increased blood pressure and heart rate.