Some people who use drugs use large enough amounts often enough and long enough to become dependent.

Definitions

A single definition for drug dependence is elusive. Concepts that aid in defining drug dependence are tolerance and psychologic and physical dependence.

Tolerance describes the need to progressively increase the drug dose to produce the effect originally achieved with smaller doses.

Psychologic dependence includes feelings of satisfaction and a desire to repeat the drug experience or to avoid the discontent of not having it. This anticipation of effect is a powerful factor in the chronic use of psychoactive drugs and, with some drugs, may be the only obvious reason for intense craving and compulsive use. Craving and compulsion to use a drug lead to using it in larger amounts, more frequently, or over a longer period than was intended when use began. Psychologic dependence involves giving up social, occupational, or recreational activities because of drug use, as well as persistent use despite knowing that the drug is likely causing a physical or mental problem. Drugs that cause psychologic dependence often have ≥ 1 of the following effects:

• Reduced anxiety and tension
• Elation, euphoria, or other pleasurable mood changes
• Feelings of increased mental and physical ability
• Altered sensory perception
• Changes in behavior

Drugs that cause chiefly psychologic dependence include marijuana, amphetamine, 3,4-methylenedioxymethamphetamine (MDMA), and hallucinogens, such as lysergic acid diethylamide (LSD), mescaline, and psilocybin.

Physical dependence is manifested by a withdrawal (abstinence) syndrome, in which untoward physical effects occur when the drug is stopped or when its effect is counteracted by a specific antagonist. Drugs that cause strong physical dependence include heroin, alcohol, benzodiazepines, and cocaine. Abstinence syndromes are drug-specific or drug class–specific and may vary considerably based on the amount and frequency of use and on patient characteristics, which may affect how patients experience withdrawal.

Addiction, a concept without a consistent, universally accepted definition, is used here to refer to compulsive use and overwhelming involvement with a drug, including spending an increasing amount of time obtaining the drug, using the drug, or recovering from its effects. It may occur without physical dependence. Addiction implies the risk of harm and the need to stop drug use, regardless of whether the addict understands and agrees.

Drug abuse is definable only in terms of societal disapproval. Drug abuse may involve the following:

• Experimental and recreational use of drugs, which is usually illegal
• Unsanctioned or illegal use of psychoactive drugs to relieve problems or symptoms
• Use of drugs because of dependence or the need to prevent withdrawal

Illicit drug use, although usually considered abuse simply because it is illegal, does not always involve dependence. Use of legal substances, such as alcohol and prescription drugs, may involve dependence and abuse. Abuse of prescription and illegal drugs cuts across all socioeconomic groups.

Recreational drug use has increasingly become a part of Western culture, although in general, it is not sanctioned by society. Some users apparently are unharmed; they tend to use drugs episodically in relatively small doses, precluding clinical toxicity and development of tolerance and physical dependence. Many recreational drugs (eg, crude opium, alcohol, marijuana, caffeine, hallucinogenic mushrooms, coca leaf) are “natural” (ie, close to plant origin); they contain a mixture of relatively low concentrations of psychoactive compounds and are not isolated psychoactive compounds. Recreational drugs are most often taken orally or inhaled. Taking these drugs by injection makes it harder to predict and control desired and unwanted effects.

Intoxication refers to development of a reversible substance-specific syndrome of mental and behavioral changes that may involve altered perception, euphoria, cognitive impairment, impaired judgment, impaired physical and social functioning, mood lability, belligerence, or a combination. Taken to the extreme, intoxication can lead to overdose, significant morbidity, and risk of death.

Narcotics and scheduled drugs: Narcotics are drugs that cause insensibility or stupor (narcosis), but the term is typically restricted to drugs that bind to opiate receptors: opium, opium derivatives, and their semisynthetic and synthetic analogues. However, the US government classifies cocaine as a narcotic, even though it does not bind at opiate receptors or have morphineSome Trade Names
DURAMORPH
MS CONTIN
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ROXANOL
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-like effects. Many narcotics (specifically opioids) are used therapeutically to induce anesthesia and to relieve pain, cough, and diarrhea. The morphineSome Trade Names
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MSIR
ROXANOL
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-like effects of opioids are welcomed in most clinical situations but contribute to the attractiveness of narcotics for abuse.

In the US, the Comprehensive Drug Abuse Prevention and Control Act of 1970 and subsequent modifications require the pharmaceutical industry to maintain physical security of and strict record keeping for certain classes of drugs (controlled substances—see Table 1: Drug Use and Dependence: Some Examples of Controlled Substances). Controlled substances are divided into 5 schedules (or classes) on the basis of their potential for abuse, accepted medical use, and accepted safety under medical supervision. The schedule classification determines how a substance must be controlled.

• Schedule I: These substances have a high potential for abuse, no accredited medical use, and a lack of accepted safety. They can be used only under government-approved research conditions.
• Schedule II to IV: Going from schedule II to IV, these drugs have progressively less potential for abuse. They have an accredited medical use. Prescriptions for these drugs must bear the physician's federal Drug Enforcement Administration (DEA) license number.
• Schedule V: These substances are least likely to be abused. Some Schedule V drugs do not require a prescription.

State schedules may vary from federal schedules.

Table 1
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Some Examples of Controlled Substances Schedule Examples I* Cannabis, GHB, heroin, LSD, MDMA, some opioids, psilocybin II Amphetamines, barbiturates (short-acting), cocaine, hydrocodone, methadoneSome Trade Names DOLOPHINE Click for Drug Monograph , methylphenidateSome Trade Names CONCERTA RITALIN Click for Drug Monograph , morphineSome Trade Names DURAMORPH MS CONTIN MSIR ROXANOL Click for Drug Monograph , other strong opioid agonists, phencyclidineSome Trade Names No US trade name III Anabolic steroids, barbiturates (intermediate-acting), buprenorphineSome Trade Names BUPRENEX SUBUTEX Click for Drug Monograph , dihydrocodeine, ketamineSome Trade Names KETALAR Click for Drug Monograph , paregoricSome Trade Names No US trade name Click for Drug Monograph IV Barbiturates (long-acting), benzodiazepines, chloral hydrateSome Trade Names NOCTEC Click for Drug Monograph , meprobamateSome Trade Names EQUANIL MILTOWN Click for Drug Monograph , pentazocineSome Trade Names TALWIN Click for Drug Monograph , propoxypheneSome Trade Names DARVON DOLENE , zolpidemSome Trade Names AMBIEN Click for Drug Monograph V Cough suppressants containing small amounts of codeineSome Trade Names No US trade name Click for Drug Monograph , pregabalin *Cannot be prescribed. GHB = gamma hydroxybutyrate; LSD = lysergic acid diethylamide; MDMA = methylenedioxymethamphetamine.

Last full review/revision July 2008 by Patrick G. O'Connor, MD, MPH

Content last modified February 2012