The terms drug dependence and drug addiction are often used interchangeably, but this practice leads to confusion among professionals regarding the diagnostic implications of these terms and also contributes to misunderstanding the underlying causes of substance use. As described earlier, drug addiction refers to a behavioral syndrome where the procurement and use of a drug seem to dominate the individual's motivation and where the normal constraints on the individual's behavior seem largely ineffective. Inherent in this definition is the overwhelmingly powerful motivation to obtain and self-administer the drug. And as noted earlier, drug abuse simply means that the substance is used in a manner that does not conform to social norms; the motivation to use the substance may or may not be particularly strong compared with other motivators. The causes of drug abuse and drug addiction can be the same, but they are very often much different. Specifically, drug addiction involves the biological action of a drug on brain reward and motivation systems, while drug abuse often involves other psychosocial factors with only modest direct effects on brain reward systems.
Drug dependence, in contrast to the two terms described above, refers to a state where the individual is dependent upon the drug for normal physiological functioning. Abstinence from the drug produces withdrawal reactions which constitute the only evidence for dependence. Drug dependence can involve disturbances in general bodily (i.e., somatic) function such as vomiting, diarrhea, sweating, and the resulting symptoms indicate a physical dependence syndrome which is usually specific for a given class of drug. Drug dependence can also involve disturbances in psychological functioning, such as inability to concentrate, anxiety, depression, and the resulting symptoms indicate a psychological dependence syndrome which often shares common features with other abused drugs. It is important to note that psychological dependence has a physiological basis and thus it is preferable to use the term physical dependence to refer to disturbances in somatic function to avoid confusion.
A number of substances produce psychological and/or physical dependence without producing an addiction. The therapeutic uses of certain steroids, antidepressant medication of the SSRI class, and even some antihistamines all produce characteristic withdrawal syndromes when their use is abruptly discontinued. However, there is no strong motivation to continue the use of these substances for most patients; some patients even refuse to resume treatment with such drugs because of their adverse experience during unsupervised withdrawal.
Other substances can produce a notable psychological dependence without producing an exceptionally strong motivation to avoid abstinence. Caffeine has desirable stimulating effects that involve general arousal accompanied by a mild mood elevation for many daily coffee drinkers. And while the avid coffee drinker usually chooses not to miss their morning or afternoon ‘brew,’ many voluntarily abstain when the cost is too high ($8 for a cup of coffee in NYC?) or access is difficult. The ensuing abstinence syndrome has both psychological (e.g., lethargy) and physical (e.g., mild headache) withdrawal signs, but the motivation to abate this condition is far below the level produced by highly addictive drugs such as cocaine and heroin.
Physical dependence often occurs without addiction (e.g., therapeutic use of steroids, SSRIs), and addiction can occur without appreciable physical dependence (e.g., cocaine). Similarly, psychological dependence can occur without addiction (e.g., morning coffee for millions of regular users), but it’s not clear whether addiction ever occurs without psychological dependence. And of course drug abuse may or may not be accompanied by drug dependence and addiction.
The fact that notable signs of physical dependence occur with some of the more addictive drugs (e.g., heroin, barbiturates, alcohol) has lead many to mistakenly attribute the motivation for substance use to the avoidance of withdrawal discomfort. Other drugs, such as the psychomotor stimulants, do not produce these characteristic withdrawal reactions and have helped to debunk this common misconception. Of course there are other compelling lines of evidence that physical dependence is not the primary cause of drug addiction (see Bozarth, 1989, 1990, 2009; Bozarth & Wise, 1984; Wise & Bozarth, 1987) although it can contribute to the overall motivation for continued drug use (see Bozarth, 1994).
In summary, drug addiction describes the motivational strength of substance use; drug abuse describes the misuse of a substance without explicit reference to motivational strength; and drug dependence describes the necessity of using a substance to maintain normal psychological and/or somatic functioning without reference to the motivational strength of the substance use or to whether the substance use violates cultural norms. These three terms have distinctively different meanings although there are obvious and numerous cases where all three apply to the same drug-use situation (i.e., the individual may be dependent upon a drug which they abuse because they are addicted).
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