Dependence and Addiction
In the previous lecture, we covered two critical aspects of habitual drug use, tolerance and withdrawal. Today, we are going to discuss dependence and addiction.
Drug addiction is an immensely serious and largely misunderstood public health concern. The National Survey on Drug Use and Health reports that almost 20 million American adults are dealing with a substance use disorder (SUD). Furthermore, about one-third of people with an SUD also have an additional psychiatric disorder. That is a lot of people and a lot of suffering.
Substance use disorder is the preferred scientific term for addiction, but in reality, both are often used interchangeably. Sadly, there remains a substantial stigma surrounding addiction and a lot of myths as to why and how people become addicted to drugs. Perhaps the biggest myth is that addiction is some kind of moral failing and continued use of drugs is “just a choice”. In short, this is an incredibly simplistic way of looking at the issue, and it is factually incorrect. In reality, addiction is complex and involves social, psychological, and physiological causes.
Let’s start with a key aspect of addiction, dependence. It is commonly assumed that people who chronically abuse drugs do so because they are physically hooked. This is part of the story of addiction, but does not sufficiently explain it. Dependence means that physical changes in the body have occurred after repeated drug use, to the point where both tolerance and withdrawal symptoms have developed. Now, most forms of drug addiction (e.g., tobacco, cocaine, opioids) present with tolerance and withdrawal, but so do other classes of drugs not associated with addiction. For example, at any one point in time, a large proportion of adults are taking an antidepressant medication, most commonly a selective serotonin reuptake inhibitor (SSRI). With SSRIs, tolerance is possible, and withdrawal symptoms are common and can be uncomfortable. Yet, people dependent on an SSRI do not typically display drug-seeking behavior, or a compulsive urge to get their hands on the drug.
Addiction involves physical dependence plus “something more”. To diagnose an SUD, psychiatrists and psychologists rely on the Diagnostic and Statistical Manual of Mental Disorders (DSM–5) published by the American Psychiatric Association. The DSM-5 lists eleven different symptoms of an SUD. These symptoms focus on aspects of drug use such as cravings, an inability to cut back or stop, tolerance, withdrawal symptoms, and harm to the person’s relationships and career. An SUD diagnosis must be made by a clinician (e.g., psychiatrist) and involves meeting at least two of the eleven criteria. The more criteria that are met, the more severe the SUD generally. This is by no means a perfect definition for an SUD (or addiction), but it is considered to be the gold standard. The DSM-5 is useful for describing what an SUD is, and for diagnosing it based on a set of criteria; however, it does not offer much in the way of explaining how addiction develops.
For decades, both defining what addiction is, and ultimately what causes it, has been a complicated puzzle for the medical community. Our understanding of addiction has evolved over time based on research findings and new neuroimaging technology such as fMRI and positron emission tomography (PET). There are numerous theories of addiction, too many to cover here, but let’s look at the most dominant frameworks for conceptualizing addiction.
The Brain Disease Model of Addiction focuses on the role of the brain’s reward system in addiction. Recall from our previous lecture, dopamine neurons in the reward circuitry fire after we have experienced a natural reward such as food or sex. These are natural rewards that are critical for the survival of our species. Furthermore, once we eat a certain amount of food, we become satiated and don’t want anymore. Dopamine transmission then drops back to normal levels. However, drugs of abuse result in substantial dopamine release. After repeated use of the drug, dopamine neurons no longer function normally. As a result, the use of the drug no longer produces the same amount of euphoria, meaning that larger and larger doses are needed. Simultaneously, natural rewards like food also become less rewarding. Drugs of abuse hijack the reward system, and other rewards lose their appeal.
Drugs also capture our attention. The Incentive Sensitization Theory of addiction, introduced by Terry Robinson and Kent Berridge, suggests that environmental cues associated with a drug become conditioned (learned) with the drug over time. Eventually, merely seeing the drug cues (e.g., an alley, needles, glassware for smoking) can activate the dopamine system and lead to strong cravings for the drug. Not only that, but the person becomes hypersensitive to noticing those cues over other stimuli in the environment. Combined, neurobiological changes and increased attention to drug cues make it incredibly difficult to stop using the drug and leave the person very susceptible to relapse. Therefore, addiction happens after substantial alterations to the person’s brain resulting from the drug itself as well as conditioning.
Beginning with the next lesson, we are going to start covering individual drugs and their effects on us. Tomorrow we’ll start by looking at alcohol. See you then!
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