People use drugs for a variety of reasons, including recreational or social, sensation-seeking, and religious or spiritual purposes; the achievement of altered states; as a sign of rebellion and alienation; and as a result of peer pressure. Usage usually involves a combination of reasons.Drugs are commonly classified according to the physiological effect they create. The five classifications are stimulants, depressants, hallucinogens, narcotics, and inhalants. Caffeine is probably the most used drug in America. It is a stimulant that speeds heart rate, increases blood pressure, and can cause insomnia. Alcohol is a socially acceptable drug that is a major source of physical and emotional damage and death.The blood alcohol concentration of ethyl alcohol is affected by the rate of consumption, the type of alcoholic beverage being consumed, the body weight of the individual drinking, and the drinker's tolerance to alcohol. Alcoholism is a disease in which a person loses control over drinking. Determining who will be­come an alcoholic is impossible. Alcoholism crosses all social, sexual, educational, and racial barriers. Nicotine is an addictive agent found in tobacco. The tars found in tobaccos are carcinogenic agents.The carbon monoxide formed when tobacco is smoked interferes with the body's ability to trans­port oxygen and increases the risk of heart attacks and strokes. Side stream smoke has even higher concentrations of these agents than the smoke inhaled by the smoker. Cocaine use has become epidemic in the United States. Cocaine can be snorted, injected, or free­based (smoked). The consequences of cocaine use range from headaches and nausea to violence and death. Cocaine addiction is difficult to overcome . The primary psychoactive ingredient in marijuana and hashish is delta-9-tetrahydrocannabinol. Carcinogens can be found in more potent levels in marijuana than in tobacco. Hashish is more potent than marijuana. Short-term effects of marijuana use include euphoria and perceptual impairment. Some people experience anxiety, a sense of depersonalization, and hallucinations. Long-term effects are not well documented. Some drugs have been abused by society for many years. They include heroin, methamphetamine (crank), and LSD. The newest form of methamphetamine is ice, which is smokable and more addictive, potent, and destructive than crack cocaine. Designer drugs are analogs of controlled substances and are more powerful and less predictable in the effects they create.