What is physiological dependence?
Physiological dependence occurs when the body adapts to the continued presence of a drug. These adaptations lead to negative symptoms when the drug is removed or when the dose is dramatically reduced. As such, the presence of a drug-specific withdrawal syndrome, or a set of symptoms associated with drug removal, provides evidence for physiological dependence.
Many researchers use the term physiological dependence a bit more broadly, though, and would define it as including both tolerance and withdrawal. Tolerance refers to the need to increase the dosage of a drug in order to achieve the same effect across time and with repeated dosing. In other words, with more experience taking the drug, more of the drug must be taken to maintain the drug’s effectiveness.
Alcohol and opiate drugs, such as heroin, produce classic physiological dependence. For example, when a person takes an opiate drug, the initial effects include analgesia, euphoria, and constipation. If the person takes the drug only occasionally, the body may not adapt to the presence of the drug in significant ways; therefore, the same dose may be sufficient to produce the initial effects. However, if the drug is taken repeatedly, tolerance may develop in a matter of weeks or even days. The initial dose will no longer be as effective in reducing pain or in increasing euphoria and constipation. If one wants to maintain the initial effects, the dose will need to be increased and will continue to need to be increased as more and more tolerance develops.
The drugged state is the body’s new normal. One can observe how much the body has adapted to operating in the presence of a drug by observing the drug-specific withdrawal symptoms after the drug is removed (or stopped). In cases of physiological dependence, withdrawal symptoms are basically the opposite of the effects produced by the drugs themselves. These often unpleasant symptoms can be easily eliminated, with another dose of the drug. Though alcohol also produces tolerance and withdrawal, the specific symptoms will be quite different, because the effects of the drug itself are different, requiring different adaptations.
Physiological dependence has been considered synonymous with the concept of addiction. Some researchers contend that there is no distinction between physiological and psychological dependence. However, others posit that physiological dependence more strongly characterizes addictions to drugs with strong physical withdrawal symptoms (such as opiates and alcohol, which can cause flu-like symptoms and seizures, respectively, during withdrawal) and that psychological dependence characterizes addictions to drugs that do not display strong physical withdrawal symptoms, such as marijuana or cocaine, although withdrawal from these substances can produce symptoms such as anxiety, sleep disturbances, fatigue, and depression.
Repeated abuse of a drug can produce a number of psychological symptoms of dependence, including a preoccupation with the drug, a pattern of escalating and uncontrolled use, and other maladaptive behavior changes. Some drugs of abuse have a higher probability of producing psychological dependence but vary dramatically in the extent to which they produce clear drug-specific symptoms of withdrawal. However, in some cases drugs that were not thought to produce clear physiological dependence (such as cocaine and marijuana) have since been found to do so.
Finally, the opposite can be true as well. Some drugs may produce strong physiological dependence without producing strong psychological dependence. A good example of this is caffeine. The most noticeable withdrawal symptom of caffeine dependence is headache, which can easily be alleviated with another cup of coffee or a caffeinated beverage. Caffeine headaches are clear and consistent markers of physiological dependence, but having these headaches are not associated with addiction. That is, daily coffee drinkers with caffeine headaches are not considered to be addicted because they rarely exhibit the maladaptive behavioral changes associated with addiction.
The vast majority of caffeine drinkers, though they may be physiologically dependent upon caffeine, are not psychologically dependent in any clinically relevant way. Most habitual coffee drinkers do not become preoccupied with caffeine; they do not typically develop escalating and uncontrolled patterns of caffeine use or other maladaptive behavioral changes.
Most acute withdrawal symptoms last for days, but in some cases they can be extraordinarily unpleasant (as is the case with opiates) and even medically dangerous (as is the case with alcohol). Therefore, the treatment of many addictions must begin with treating the withdrawal symptoms. This is particularly important in alcohol treatment, where withdrawal symptoms can include life-threatening seizures.
Substitute drugs that have some central nervous system effects in common with alcohol can be provided for a period of time, as the brain and body adjust to the removal of alcohol. Effective drugs for alleviating symptoms of alcohol include a class of tranquilizing drugs called the benzodiazepines. The benzodiazepines themselves, however, also can produce physiological dependence. This illustrates an important challenge for drug treatment.
Ideally, one would like to alleviate the symptoms of withdrawal without perpetuating or worsening physiological dependence. This may not always be easy to accomplish, as substitute drugs that are effective in treating withdrawal often produce physiological dependence themselves. Another example is methadone treatment of opiate withdrawal.
An additional challenge in treating physiological dependence is the possibility of negative symptoms that persist beyond the period of acute withdrawal. These symptoms are referred to as post-acute withdrawal symptoms (PAWS) and can include anhedonia (the inability to experience pleasure), drug craving, tendency to relapse to using the drug, and cognitive impairment. These symptoms are far less drug-specific, may occur to some extent even with drugs that do not produce acute withdrawal effects, and can last for months, years, or even decades after the initial withdrawal from the drug of abuse. Though less understood, PAWS may indicate that the notion of physiological dependence may need to be expanded with improved understanding of these longer-lasting changes.
"Dependence Syndrome." World Health Organization. WHO, n.d. Web. 27 Oct. 2015.
Julien, Robert M., Claire D. Advokat, and Joseph E. Comaty. A Primer of Drug Action. 12th ed. New York: Worth, 2011. Print.
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