Behavior associated with a dependence on either a substance or activity that is harmful when used to excess. When addicted, the user is either unable or unwilling to stop his or her behavior. In the compulsive need for and use of a drug, addiction can involve either a physical or a psychological need. When addicted, the user also experiences increased tolerance for a substance. When more broadly defined, addiction can also refer to the compulsive need for an activity i.e. “addicted to TV,” or “addicted to jogging.” Addiction is measured in the degree of harm that it causes the user. Thus, an addiction to coffee is not considered a serious addiction because science has not shown that coffee consumption produces significant health hazards. An addiction to heroin is considered extremely harmful because of the physical and social conditions commonly associated with heroin addiction: HIV, hepatitis, endocarditis, cellulitis, overdose and collapsed veins. In the early twenty-first century, addictions to activities such as sex, gambling, video games, the Internet and pornography are talked about frequently.

Some substances which are physically addictive and used illegally include opiates, stimulants, inhalants, depressants and barbiturates. New drugs of the 1980s and 1990s that appeal to young people in dance clubs are Ecstasy an amphetamine/ hallucinogen combination drug and ketamine (Special K), a depressant. The National Institute on Drug Abuse estimates that 1.5 million people in the US over the age of twelve were chronic cocaine users, and about 2.4 million people have used heroin at some point in their lives.

The most widespread addictions in the United States, however, are tobacco and alcohol, both legal mindaltering substances. NIDA estimates that in 1996 there were 62 million smokers in the US, and an additional 6.8 million who used smokeless tobacco.

Treatment for addictions come in many different forms. For drugs which are clearly physically addictive, like heroin, substitution treatment is available. Methadone is most commonly substituted for heroin, and is strictly regulated by the federal government.

Methadone programs are located mainly in large cities, so addicts who live in rural areas and small towns either do not have access to methadone treatment, or may have to travel many hours to get to an available clinic. New forms of heroin substitution, such as buprenorphine, are also available.

Abstinence-based programs often use a “12-step” approach which was developed by Alcoholics Anonymous, and has since been adopted by Narcotics Anonymous, Cocaine Anonymous, Gambling Anonymous, and other national projects that seek to support addicts who are “in recovery” from their addictions. The 12-step approach, since it is based on submitting to a higher power or religious figure, has some critics. Alternatives to 12-step programs have also arisen, which often center the addict as the controlling party in the process of recovery rather than a higher authority.

During the 1990s a new philosophy of treating the harms associated with drug use emerged. Harm reduction calls for prevention and treatment programs which do not expect that abstinence is the only option for dealing with the consequences of drug use.

Instead, harm reduction proponents advocate measures which will decrease the harms associated with illicit drug use, i.e. prevent HIV transmission, overdoses and other diseases associated with using dirty syringes. Needle exchange programs which prevent bloodborne diseases among injecting addicts are good examples of harm reduction programs, and are springing up in areas of the country where drug use and drug traffic are more common.