Addiction

• 1. Introduction

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  Addiction is a neuropsychological disorder marked by a persistent and intense urge to use a drug or perform a behavior that delivers an immediate psychological reward, even when the harm is substantial. When mice were given cocaine, they revealed the compulsive and involuntary core of the condition. In humans, it is far more tangled, bound up with behavior and personality traits. The same brain machinery that responds to food or to falling in love can be reshaped by repetitive drug use, perpetuating craving and weakening self-control in people with pre-existing vulnerabilities. How does a chemical or a habit hijack circuitry built for survival? Why do genetics and environment each appear to carry roughly half the weight? And how did a Latin word meaning to give oneself over become the name for compulsion? The answers run from a single transcription factor in the brain to an art exhibition designed to change how the public sees a chronic illness.

• 2. The Reward Pathway

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  Dopamine is the primary neurotransmitter of the brain's reward system, governing movement, emotion, cognition, motivation, and feelings of pleasure. Virtually all drugs that cause addiction increase dopamine release along the mesolimbic pathway. That pathway, also called the mesocorticolimbic pathway, links several brain regions in a chain. The ventral tegmental area, or VTA, holds a network of dopaminergic neurons that fire when stimuli signal a reward is near. These neurons release dopamine into the nucleus accumbens, a structure built mainly of GABAergic medium spiny neurons. The nucleus accumbens helps acquire and trigger conditioned behaviors, and its sensitivity to drugs climbs as addiction progresses. The prefrontal cortex, including the anterior cingulate and orbitofrontal cortices, forms a separate VTA output. It is critical for linking the rewarding experience of drug use to cues in the environment. Those cues become powerful drivers of drug-seeking, able to trigger relapse even after months or years of abstinence. Prolonged, abnormally high dopamine in the synaptic cleft can downregulate receptors, dulling sensitivity to natural reinforcers. Drug-seeking itself is induced by glutamatergic projections running from the prefrontal cortex into the nucleus accumbens. Inhibiting AMPA glutamate receptors and glutamate release in that region can prevent the behavior. The basolateral amygdala feeds into the nucleus accumbens and is thought to carry motivation, while the hippocampus contributes through learning and memory.

• 3. The Molecular Switch

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  DeltaFosB, written as ΔFosB, is a gene transcription factor and the common factor across virtually all forms of behavioral and drug addiction. Two decades of research have shown that addiction arises, and its compulsive behavior intensifies or fades, alongside the overexpression of ΔFosB in the D1-type medium spiny neurons of the nucleus accumbens. Because of this causal link, ΔFosB serves preclinically as an addiction biomarker. Chronic addictive drug use alters gene expression in the mesocorticolimbic projection, driven mainly by three transcription factors: ΔFosB, cAMP response element binding protein known as CREB, and nuclear factor kappa B known as NF-κB. ΔFosB has been implicated in addictions to alcohol, amphetamine and other substituted amphetamines, cannabinoids, cocaine, methylphenidate, nicotine, opiates, phencyclidine, and propofol, among others. CREB works in the opposite direction. Its activity in the nucleus accumbens lowers a user's sensitivity to a substance's rewarding effects and is tied to psychological dependence and to the loss of pleasure or motivation during withdrawal. Two molecules counter ΔFosB directly: ΔJunD, a transcription factor, and G9a, a histone methyltransferase. Raising ΔJunD through viral vector-mediated gene transfer, or raising G9a by pharmacological means, can reduce and with a large enough increase even block the changes ΔFosB drives. The same factor governs natural rewards. ΔFosB in the nucleus accumbens is critical for the reinforcing effects of sexual reward, and palatable food, sex, and exercise all induce it. Because of this overlap, ΔFosB inhibitors that oppose its action may be an effective treatment for addiction.

• 4. Beyond Drugs

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  Stanton Peele, a psychologist, popularized the idea that addiction can exist without psychotropic drugs. These are termed behavioral addictions, compulsions to engage in a natural reward despite adverse consequences. Sexual behavior, eating, gambling, playing video games, and shopping all link to compulsive behavior in humans and activate the mesolimbic pathway and other parts of the reward system. Preclinical evidence shows that repeated, excessive exposure to a natural reward drives the same rise in ΔFosB expression, and the same neuroplasticity, as a drug addiction. The diagnostic manuals disagree on how far this category extends. The DSM-5 and ICD-10 recognize only gambling among behavioral addictions, while the ICD-11 also recognizes gaming addictions. Food sits in an unsettled space. Its criteria have not been categorized in references like the DSM and rest on subjective experience, much as substance use disorders do. Long-term excessive intake of foods high in fat, salt, or sugar, such as chocolate, can produce an addiction resembling drugs, because they trigger the brain's reward system. Highly palatable foods send signals that can override the body's cues for fullness, leaving persistent cravings. A person with a strong liking for chocolate may call themselves a chocoholic. The Yale Food Addiction Scale, version 2.0, is the current standard measure, developed in 2009 at Yale University. It uses a 25-item self-report questionnaire to address 11 substance-related and addictive disorders, and a potential diagnosis turns on the presence of at least two of those eleven plus significant impairment to daily activities.

• 5. Nature And Nurture

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  Genetic and environmental risk factors each account for roughly half of an individual's risk of developing an addiction, while the contribution from epigenetics remains unknown. Even someone with relatively low genetic risk can become addicted after exposure to high enough doses of an addictive drug over weeks to months. Genetic factors account for 40 to 60 percent of the risk for alcoholism, with similar heritability indicated for other drug addictions, including genes encoding the Alpha5 Nicotinic Acetylcholine Receptor. Knestler hypothesized in 1964 that a gene or group of genes might shape predisposition, for instance by altering levels of a normal protein and changing how specific brain neurons develop. Twin studies offer some of the strongest evidence: if one twin is affected, the other is likely affected too, and by the same substance. Family studies point the same way, with relatives of an affected member at far higher risk. Much of the gene-specific data stays mixed. Common variants with allele frequencies above 5 percent confer only small additional risk, with odds ratios around 1.1 to 1.3, which led to the rare variant hypothesis that genes below 1 percent frequency carry much greater risk. Genome-wide association studies rarely identify the genes found through animal knockout models, often surfacing genes tied to processes such as cell adhesion instead. Environment supplies the other half. The brain disease model holds that exposure to an addictive drug is the single most significant environmental risk factor, though many researchers, including neuroscientists, call that model misleading and incomplete. The National Institute on Drug Abuse cites lack of parental supervision, peer substance use, substance availability, and poverty as risk factors among children and adolescents. After the nationwide outbreak of COVID-19 in China, more people quit than started smoking, and smokers on average cut back. Travis Hirschi's social control theory holds that adolescents with stronger attachments to family, religious, academic, and other institutions are less likely to drift into the delinquent behavior that can lead to addiction.

• 6. The Adolescent Window

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  Most individuals first encounter and use addictive drugs during their teenage years. In the United States there were just over 2.8 million new users of illicit drugs in 2013, about 7,800 new users per day, and 54.1 percent of them were under 18. In 2011, roughly 20.6 million people in the United States over the age of 12 had an addiction, and over 90 percent of those with an addiction began drinking, smoking, or using illicit drugs before turning 18. The vulnerability is built into brain development. The prefrontal cortex, responsible for planning, inhibitory control, and weighing long-term consequences, undergoes major maturation during adolescence. The limbic reward circuits mature earlier than the prefrontal regulatory networks, leaving reward sensitivity high while cognitive control lags. Neuroimaging shows that adolescents have reduced prefrontal activation during decision-making, more risk-taking, and heightened dopamine reactivity compared with adults. This mismatch pushes them to act on impulse before weighing consequences. Once addicted, adolescents are more resistant to treatment and more prone to relapse. Substance exposure during this window can disrupt synaptic pruning and myelination, producing long-term changes in executive functioning and reward processing. Stress deepens the danger across all ages. Acute and chronic stress activate the hypothalamic-pituitary-adrenal axis, raising cortisol and corticotropin-releasing factor, which lift the motivational value of substances that briefly ease negative feelings. Adverse childhood experiences carry a strong dose-response relationship with later substance use disorder, documented by the Adverse Childhood Experiences Study from the Centers for Disease Control and Prevention. Stress is also one of the most reliable predictors of relapse, with neuroimaging linking amygdala activation and reduced prefrontal regulation to craving and a return to use.

• 7. Diagnosis And Defense

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  The DSM-5 discourages the term drug addiction, citing its uncertain definition and potentially negative connotation, and prefers substance use disorder to span the range from mild to severe. In the DSM-5, drug addiction is synonymous with severe substance use disorder, and the manual grades cases as mild, moderate, or severe by counting how many diagnostic criteria are present. The ICD-11 takes a different route, first separating disorders due to substance use from disorders due to addictive behaviors, then offering three diagnostic possibilities for substances: an episode of harmful use, a harmful pattern of use, and substance dependence. Older editions leaned on physical dependence and withdrawal. Withdrawal symptoms can include body aches, anxiety, irritability, intense cravings, nausea, hallucinations, headaches, cold sweats, tremors, and seizures. During acute opioid withdrawal, restless legs symptoms are common and may be profound, the phenomenon that gave rise to the idiom kicking the habit. Several screening tools sharpen diagnosis. The CRAFFT, version 2.1, identifies substance use and related driving risk among adolescents, with a nicotine version called CRAFFT 2.1+N. The Drug Abuse Screening Test, copyrighted by Dr. Harvey A. Skinner, scores responses from zero to 28, flagging abuse or dependence at a cutoff of 6. The Alcohol, Smoking, and Substance Involvement Test, built by the WHO, runs through eight interview questions. Prevention research has looked further ahead, toward vaccines investigated since the early 2000s that would train the immune system to disable a drug's molecules before they reach the brain. NicVAX targets nicotine, TA-CD combines norcocaine with inactivated cholera toxin to block cocaine from crossing the blood-brain barrier, and TA-NIC raises antibodies against nicotine. As of September 2023, a vaccine had been tested against heroin and fentanyl and was on its way to testing against OxyContin.

• 8. A Word And Its Image

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  The word addiction derives from the Latin addico, meaning giving over, carrying both devotion and the darker sense of being enslaved to a creditor under Roman law. That dual meaning survived in traditional English dictionaries, which held both legal surrender and personal devotion. In early modern Europe, during an era of Christian revivalism and Pietistic tendencies, the word leaned toward goodness and meant devoting oneself to another. The 19th-century temperance movements narrowed it to a drug-related disease, ignoring behavioral addictions and the possibility of positive or neutral ones. The suffix -holic carries its own odd history. It was pulled from alcoholism, one of the first addictions identified both medically and socially, by misdividing the word into alco and -holism. Correct medico-legal terms already existed: dipsomania for alcoholism, choreomania for a danceaholic, ergomania for a workaholic, saccharomania for a sugarholic. Modern research traces back to studies of morphine addiction in 1875, which helped establish addiction as a medical condition rather than a moral failing. That reframing continues today through art. Creative activities like painting, sculpting, music, and writing let people express feelings when verbal communication fails, and the Formal Elements Art Therapy Scale, or FEATS, evaluates drawings by people with substance use disorders using twelve elements, three of them, Person, Realism, and Developmental, especially good at distinguishing those drawings from a control group. Art also serves advocacy. The Temple University College of Public Health ran a project asking students to create pieces about opioid use, displayed on a website and promoted through social media, and the interviews afterward revealed a shift in perspective. A project called Voice gathered art, poetry, and narratives from women with histories of addiction, shown at venues including an International Conference on Drug Related Harm, aiming to move the public from seeing addiction as a moral failing to understanding it as a chronic medical condition.