Overview
Dependence in the context of substance use refers to a body or mind’s reliance on using a substance to function normally, such that reduction or cessation of use can produce distress or induce symptoms of withdrawal.
The National Cancer Institute defines “physical dependence” as:
“A condition in which a person takes a drug over time, and unpleasant physical symptoms occur if the drug is suddenly stopped or taken in smaller doses.” 1
This is a perfectly fine functional definition, but it should be noted that there has been strong ongoing debate about the distinction between dependence and addiction, with the former often conceptualized as a state observed primarily through physiological evidence and the latter as a long-term disorder of behavioral patterns and mental processes. I speak in generalities here. For instance, the ICD-11 centralizes “Alcohol Dependence” as the primary presentation of “alcohol use disorder,” with “Harmful Alcohol Use” as a separate disorder that’s determined through the harm caused to oneself and others rather than evidence of dependence.
The ICD-11 provides several definitions for dependence based on the substance being used, so to use “6C40.2 Alcohol dependence” as an example:
“Alcohol dependence is a disorder of regulation of alcohol use arising from repeated or continuous use of alcohol. The characteristic feature is a strong internal drive to use alcohol, which is manifested by impaired ability to control use, increasing priority given to use over other activities and persistence of use despite harm or negative consequences. These experiences are often accompanied by a subjective sensation of urge or craving to use alcohol. Physiological features of dependence may also be present, including tolerance to the effects of alcohol, withdrawal symptoms following cessation or reduction in use of alcohol, or repeated use of alcohol or pharmacologically similar substances to prevent or alleviate withdrawal symptoms. The features of dependence are usually evident over a period of at least 12 months but the diagnosis may be made if alcohol use is continuous (daily or almost daily) for at least 3 months.”
The ICD-11 also includes a list of “Diagnostic Requirements” when evaluating a patient’s alcohol use:
“A pattern of recurrent episodic or continuous use of alcohol with evidence of impaired regulation of alcohol use that is manifested by two or more of the following:
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Impaired control over alcohol use (i.e., onset, frequency, intensity, duration, termination, context);
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Increasing precedence of alcohol use over other aspects of life, including maintenance of health, and daily activities and responsibilities, such that alcohol use continues or escalates despite the occurrence of harm or negative consequences (e.g., repeated relationship disruption, occupational or scholastic consequences, negative impact on health);
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Physiological features indicative of neuroadaptation to the substance, including: 1) tolerance to the effects of alcohol or a need to use increasing amounts of alcohol to achieve the same effect; 2) withdrawal symptoms following cessation or reduction in use of alcohol (see Alcohol Withdrawal), or 3) repeated use of alcohol or pharmacologically similar substances to prevent or alleviate withdrawal symptoms.
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The features of dependence are usually evident over a period of at least 12 months but the diagnosis may be made if use is continuous (daily or almost daily) for at least 3 months.”
Interestingly, the ICD-11 also clarifies that:
“For alcohol, a specifier is used to describe the pattern of substance use or remission. Unlike for other substances, a distinction is made between continuous and episodic use…”
Though the ICD-11 itself doesn’t explicitly give the rationale for treating alcohol differently than other substances, many researchers have commented that:
“The process by which ICD-11 diagnoses have been made is described and may be summarized as a conceptual–pragmatic–confirmatory one.”
Put simply, the process of designing and including diagnoses involves a conceptual model construction from thousands of studies across disciplines, a pragmatic evaluation of clinical needs and capacities for a diagnostic label to monitor, and confirmatory stress tests in the field to assess the success of the diagnoses when actually applied to patients worldwide. This means sociopolitical and cultural factors that influence behaviors surrounding substance use become substantial considerations. For instance, alcohol is widely available and normalized as part of social or religious rituals in most parts of the world, and since it is unlikely to produce intensely fatal symptoms after immediate use, many with alcohol use disorder go through periods of sobriety and low-risk drinking between high-risk heavy drinking phases that we might call a bender.