Drug Abuse and Addiction

Introduction

This chapter explores the neurobiology, psychology, and societal aspects of drug abuse and addiction. It covers definitions, epidemiology, mechanisms of action, diagnostic criteria, and models of addiction, as well as the factors influencing drug use and dependence.

Epidemiology and Definitions

Prevalence and Patterns of Use

• Drug Abuse: The use of a drug in a manner that deviates from the approved medical or social patterns within a given culture.

• Addiction: A chronic, relapsing disorder characterized by compulsive drug seeking, continued use despite harmful consequences, and long-lasting changes in the brain.

• According to the 2016 National Survey on Drug Use and Health, a significant portion of Americans have used alcohol, tobacco, or illicit drugs.

• The most commonly used illicit drug in the United States is marijuana.

• Most illicit drug users are in the 18-25 year-old age range.

Historical and Legal Context

Development of Drug Laws

• The Controlled Substances Act (1970) created schedules of controlled substances and established penalties for possession and distribution.

• Schedules are based on medical use and potential for abuse:

• The Harrison Act (1914) regulated the use and dispensing of opioid drugs and cocaine.

Neurobiology of Addiction

Reward Pathways and Neurotransmitters

• All drugs of abuse activate the mesolimbic dopamine pathway, which mediates reward.

• Dopaminergic activity in the nucleus accumbens is essential for drug reward.

• The extended amygdala (including the central nucleus of the amygdala and bed nucleus of the stria terminalis) is involved in the negative emotional states of withdrawal.

• Other neurotransmitters involved: glutamate, GABA, serotonin, norepinephrine, and CRF (corticotropin-releasing factor).

Neuroadaptations and Sensitization

• Repeated drug exposure leads to neuroadaptations, such as changes in gene expression (e.g., increased ΔFosB in the nucleus accumbens).

• Incentive-sensitization theory: Distinguishes between drug 'liking' (pleasure) and drug 'wanting' (craving).

• As addiction develops, the user experiences an increase in wanting (incentive salience) even as 'liking' may decrease.

Diagnostic Criteria and Models of Addiction

DSM-5 Substance-Related Disorders

• The DSM-5 groups drugs into "substance-related and addictive disorders."

• Includes both substance and non-substance (behavioral) addictions, such as gambling disorder.

• Criteria include tolerance, withdrawal, loss of control, and continued use despite harm.

Models of Addiction

• Medical model: Views addiction as a brain disease with biological underpinnings.

• Moral model: Considers addiction a result of personal choice or moral failing.

• Biopsychosocial model: Integrates biological, psychological, and social factors.

Factors Influencing Drug Abuse and Addiction

Genetic and Environmental Factors

• Genetic predisposition: Family and twin studies show heritability of addiction risk.

• Genome-wide association studies (GWAS) identify genes associated with addiction vulnerability.

• Environmental factors: Stress, peer influence, and early exposure increase risk.

• Epigenetic changes (e.g., DNA methylation) can modify gene expression in response to drug exposure.

Psychological and Social Factors

• Self-medication hypothesis: Individuals may use drugs to cope with anxiety (e.g., alcohol) or depression (e.g., heroin).

• Personality traits (impulsivity, sensation-seeking) and psychiatric comorbidities (depression, anxiety) are risk factors.

Mechanisms of Tolerance, Dependence, and Withdrawal

Tolerance and Sensitization

• Tolerance: Decreased response to a drug after repeated use, requiring higher doses for the same effect.

• Sensitization: Increased response to a drug after repeated exposure (less common than tolerance).

• Withdrawal: Physical and psychological symptoms that occur when drug use is reduced or stopped.

Opponent-Process Theory

• Describes addiction as a cycle of initial positive reinforcement (pleasure) followed by negative reinforcement (relief from withdrawal).

• Over time, the negative emotional state (dysphoria) dominates, driving continued use.

Experimental Models and Measurement

Animal Models

• Self-administration: Animals will work (e.g., press a lever) to receive drugs, modeling human drug-seeking behavior.

• Progressive-ratio schedule: The response requirement increases until the animal stops responding (breakpoint), measuring drug motivation.

• Drug discrimination: Animals are trained to recognize the internal cues produced by drugs, used to study subjective effects.

Summary Table: Key Terms and Concepts

Conclusion

Drug abuse and addiction are complex phenomena involving biological, psychological, and social factors. Understanding the mechanisms underlying addiction can inform prevention and treatment strategies.