Drug addiction is a pathological condition. The disorder of addiction involves the progression of acute drug use to the development of drug-seeking behavior, the vulnerability to relapse, and the decreased, slowed ability to respond to naturally rewarding stimuli The Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) has categorized three stages of addiction: preoccupation/anticipation, binge/intoxication, and withdrawal/negative affect. These stages are characterized, respectively, everywhere by constant cravings and preoccupation with obtaining the substance; using more of the substance than necessary to experience the intoxicating effects; and experiencing tolerance, withdrawal symptoms, and decreased motivation for normal life activities. By the American Society of Addiction Medicine definition, drug addiction differs from drug dependence and drug tolerance.2001 "Definitions Related to the Use of Opioids for the Treatment of Pain,", the American Academy of Pain Medicine, the American Pain Society, and the American Society of Addiction Medicine

It is, both among scientists and other writers, quite usual to allow the concept of drug addiction to include persons who are not drug abusers according to the definition of the American Society of Addiction Medicine. The term drug addiction is then used as a category which may include the same persons who under the DSM-IV can be given the diagnosis of substance dependence or substance abuse. (See also DSM-IV Codes)

Drugs causing addiction

Drugs known to cause addiction include illegal drugs as well as prescription or over-the-counter drugs, according to the definition of the American Society of Addiction Medicine.

• Stimulants:
• Amphetamine and Methamphetamine
• Caffeine
• Cocaine
• Nicotine

• Sedatives and Hypnotics:
• Alcohol
• Barbiturates
• Benzodiazepines, particularly flunitrazepam, triazolam, temazepam, and nimetazepam
• Methaqualone and the related quinazolinone sedative-hypnotics

• Opiate and Opioid analgesics
• Morphine and Codeine, the two naturally-occurring opiate analgesics
• Semi-synthetic opiates, such as Heroin (Diacetylmorphine), Oxycodone, Hydrocodone, and Hydromorphone
• Fully synthetic opioids, such as Fentanyl and its analogs, Meperidine/Pethidine, and Methadone

Addictive drugs also include a large number of substrates that are currently considered to have no medical value and are not available over the counter or by prescription.