There are a number of genetic and environmental risk factors for explaining drug or alcohol abuse that vary across the population. Genetic and environmental risk factors each account for roughly half of an individual’s risk for developing an addiction; the contribution from epigenetic risk factors to the total risk is unknown. Even in individuals with a relatively low genetic risk, exposure to sufficiently high doses of an addictive drug for a long period of time (e.g., weeks to months) can result in an addiction.

Genetic and Biological Approaches to Addiction

Epidemiological studies estimate that genetic factors account for 40–60% of the risk factors for alcoholism. Similar rates of heritability for other types of drug addiction have been indicated by other studies. Overall, the data implicating specific genes in the development of drug addiction is mixed for most genes. One reason for this may be that the case is due to a focus of current research on common variants. Many addiction studies focus on common variants with an allele frequency of greater than 5% in the general population; however, when associated with the disease, these only confer a small amount of additional risk with an odds ratio of 1.1%–1.3%.

Genome-wide association studies (GWAS) are used to examine genetic associations with dependence, addiction, and drug use. These studies employ an unbiased approach to finding genetic associations with specific phenotypes and give equal weight to all regions of DNA, including those with no ostensible relationship to drug metabolism or response. These studies rarely identify genes from proteins previously described via animal-knockout models and candidate-gene analysis. Instead, large percentages of genes involved in processes such as cell adhesion are commonly identified.

Cross addiction is when one already has a predisposed addiction and then starts to become addicted to something different. If one family member has a history of addiction, the chances of a relative or close family developing those same habits are much higher than one who has not been introduced to addiction at a young age. In a recent study done by the National Institute on Drug Abuse, from 2002 to 2017, overdose deaths have almost tripled amongst male and females. In 2017, 72,306 overdose deaths happened in the United States that were reported.

Epigenetic Factors

Epigenetic genes and their products (e.g., proteins) are the key components through which environmental influences can affect the genes of an individual; they also serve as the mechanism responsible for transgenerational epigenetic inheritance, a phenomenon in which environmental influences on the genes of a parent can affect the associated traits and behavioral phenotypes of their offspring (e.g., behavioral responses to environmental stimuli). In addiction, epigenetic mechanisms play a central role in the pathophysiology of the disease; it has been noted that some of the alterations to the epigenome that arise through chronic exposure to addictive stimuli during an addiction can be transmitted across generations, in turn affecting the behavior of one’s children (e.g., the child’s behavioral responses to addictive drugs and natural rewards).

Figure 1. Reasons for addiction may be influenced by a myriad of factors, including genetic and biological, social, environmental, and personal reasons.

The general classes of epigenetic alterations that have been implicated in transgenerational epigenetic inheritance include DNA mythylation, histone modifcations, and downregulation or upregulation of microRNAs. With respect to addiction, more research is needed to determine the specific heritable epigenetic alterations that arise from various forms of addiction in humans and the corresponding behavioral phenotypes from these epigenetic alterations that occur in human offspring. More generally, the heritable behavioral phenotypes that are derived from addiction-induced epigenetic alterations and transmitted from parent to offspring may serve to either increase or decrease the offspring’s risk of developing an addiction.

Psychodynamic Approaches

The psychodynamic approach emphasizes systematic study of the psychological forces that underlie human behavior, feelings, and emotions and how they might relate to early experience. It is especially interested in the dynamic relations between conscious motivation and unconscious motivation. The psychodynamic approach may explain addiction associated with unconscious factors from the past that could create something similar to a trauma response of negative coping by substances. The negative coping by partaking in drugs and alcohol could turn into addiction easily if the unconscious factors are not resolved based on the approach.

According to Edward Khantzian’s self-medication hypothesis (SMH), a person may choose to medicate by using a drug as an “ego solvent,” which acts on parts of the self that are cut off from consciousness by defense mechanisms.^[1] According to Khantzian, drug-dependent individuals generally experience more psychiatric distress than nondrug-dependent individuals, and the development of drug dependence involves the gradual incorporation of the drug effects and the need to sustain these effects into the defensive structure-building activity of the ego itself. The addict’s choice of drug is a result of the interaction between the psychopharmacologic properties of the drug and the affective states from which the addict was seeking relief. The drug’s effects substitute for defective or non-existent ego mechanisms of defense. The addict’s drug of choice, therefore, is not random.

Khantzian revisited the self-medication hypothesis (SMH), suggesting there is more evidence that psychiatric symptoms, rather than personality styles, lie at the heart of drug use disorders. Khantzian specified that the two crucial aspects of the self-medication hypothesis (SMH) were that (1) drugs of abuse produce a relief from psychological suffering and (2) the individual’s preference for a particular drug is based on its psychopharmacological properties. The individual’s drug of choice is determined through experimentation, whereby the interaction of the main effects of the drug, the individual’s inner psychological turmoil, and underlying personality traits identify the drug that produces the desired effects.

While Khantzian takes a psychodynamic approach to self-medication, David Duncan proposed a self-medication model that focuses on behavioral factors. Duncan described the nature of positive reinforcement (e.g., the “high feeling” or approval from peers), negative reinforcement (e.g. reduction of negative affect), and avoidance of withdrawal symptoms, all of which are seen in those who develop problematic drug use, but are not all found in all recreational drug users. While earlier behavioral formulations of drug dependence using operant conditioning maintained that positive and negative reinforcement were necessary for drug dependence, Duncan maintained that drug dependence was not maintained by positive reinforcement, but rather by negative reinforcement. Duncan applied a public health model to drug dependence, where the agent (the drug of choice) infects the host (the drug user) through a vector (e.g., peers), while the environment supports the disease process through stressors and lack of support. A crucial determinant of whether a drug user develops drug abuse is the presence or absence of negative reinforcement, which is experienced by problematic users, but not by recreational users. According to Duncan, drug dependence is an avoidance behavior, where an individual finds a drug that produces a temporary escape from a problem, and taking the drug is reinforced as an operant behavior.

Personality theories of addiction are psychological models that associate personality traits or modes of thinking (i.e., affective states) with an individual’s proclivity for developing an addiction. Models of addiction risk that have been proposed in psychology literature include an affect dysregulation model of positive and negative psychological effects, the reinforcement sensitivity theory model of impulsiveness and behavioral inhibition, and an impulsivity model of reward sensitization and impulsiveness.

Research has consistently shown strong associations between affective disorders and substance use disorders. Specifically, people with mood disorders are at increased risk of substance use disorders. Affect and addiction can be related in a variety of ways as they play a crucial role in influencing motivated behaviors. For instance, affect facilitates action, directs attention, prepares the individual for a physical response, and guides behavior to meet particular needs. Moreover, affect is implicated in a range of concepts relevant to addiction: positive reinforcement, behavior motivation, regulation of cognition and mood, and reasoning and decision making. Emotion-motivated reasoning has been shown to influence addictive behaviors via selecting outcomes that minimize negative affective states while maximizing positive affective states.

Cognitive Approaches

Cognitive control, and particularly inhibitory control over behavior, is impaired in addiction. Executive functions (collectively referred to as executive function and cognitive control) are a set of cognitive processes that are necessary for the cognitive control of behavior: selecting and successfully monitoring behaviors that facilitate the attainment of chosen goals. Executive functions include basic cognitive processes such as attentional control, cognitive inhibition, inhibitory control, working memory, and cognitive flexibility. Higher-order executive functions require the simultaneous use of multiple basic executive functions and include planning and fluid intelligence (e.g., reasoning and problem-solving).

Expectancy theory proposes that an individual will behave or act in a certain way because they are motivated to select a specific behavior over others due to what they expect the result of that selected behavior will be. In essence, the motivation of the behavior selection is determined by the desirability of the outcome. However, at the core of the theory is the cognitive process of how an individual processes the different motivational elements. As related to addiction, expectancy theory explains how there may be a motivation to experience the “high” of the substance and the euphoric state that the drug brings to the body. Also, this euphoric state may motivate individuals in the future to take the substance again and again, and hence exacerbating the addiction process. Expectancy theory may also explain how some view drug use as “cool,” or that what they perceive as the benefits of drug use outweigh the consequences.

Behavioral Approaches

Behaviorists explain drug use and addiction by emphasizing the way that these behaviors are learned or habitualized. According to social learning theory, which holds that behaviors are learned through imitating and observing others, someone might be peer pressured into trying drugs for the first time. Operant conditioning, which emphasizes repeating behaviors that result in a reward, may explain why an individual would seek out a “high” or the reduction in stress they may get from using a drug. Eventually, this could lead to an increased desire to obtain or use the drug.

As mentioned above, the self-medication hypothesis argues that specific psychiatric withdrawal symptoms, which increase during abstinence, may be the main driver of persistent drug use because of negative reinforcement. Positive reinforcement theories, by contrast, argue that the excessively rewarding effects of drugs drive persistent drug use independently of the withdrawal syndrome. The challenge for positive reinforcement theories is to explain why drug use persists when addicts claim the drug has lost its value. To solve this contradiction, there are several theories like those that emphasize the classical conditioning of behaviors, where an addicted person has learned to associate certain behaviors and drug use, so that they become dependent on the drug.^[2]

Environmental Factors

Environmental risk factors for addiction are the experiences of an individual during their lifetime that interact with the individual’s genetic composition to increase or decrease their vulnerability to addiction. A number of different environmental factors have been implicated as risk factors for addiction, including various psychosocial stressors. The National Institute on Drug Abuse (NIDA) cites lack of parental supervision, the prevalence of peer substance use, drug availability, and poverty as risk factors for substance use among children and adolescents. The brain disease model of addiction posits that an individual’s exposure to an addictive drug is the most significant environmental risk factor for addiction. However, many researchers, including neuroscientists, indicate that the brain disease model presents a misleading, incomplete, and potentially detrimental explanation of addiction.

Adverse childhood experiences (ACEs) are various forms of maltreatment and household dysfunction experienced in childhood. A study of 900 court cases involving children who experienced abuse found that a vast amount of them went on to suffer from some form of addiction in their adolescence or adult life. This pathway towards addiction, which is opened through stressful experiences during childhood, can be avoided by a change in environmental factors throughout an individual’s life and opportunities of professional help. If one has friends or peers who engage in drug use favorably, the chances of them developing an addiction increases. Family conflict and home management may also lead to alcohol or other drug use.

Age

Adolescence represents a period of unique vulnerability for developing an addiction. In adolescence, the incentive-rewards systems in the brain mature well before the cognitive control center. Therefore, adolescents are increasingly likely to act on their impulses and engage in risky, potentially addicting behavior before considering the consequences. Not only are adolescents more likely to initiate and maintain drug use, but once addicted they are more resistant to treatment and more liable to relapse.

Statistics have shown that those who start to drink alcohol at a younger age are more likely to become dependent later on. About 33% of the population tasted their first alcohol between the ages of 15 and 17, while 18% experienced it prior to this. As for alcohol abuse or dependence, the numbers start off high with those who first drank before they were 12 and then drop off after that. For example, 16% of alcoholics began drinking prior to turning 12 years old, while only 9% first touched alcohol between 15 and 17. This percentage is even lower, at 2.6%, for those who first started the habit after they were 21.

Most individuals are exposed to and use addictive drugs for the first time during their teenage years. In the United States, there were just over 2.8 million new users of illicit drugs in 2013 (~7,800 new users per day); among them, 54.1% were under 18 years of age. In 2011, there were approximately 20.6 million people in the United States over the age of 12 with an addiction. Over 90% of those with an addiction began drinking, smoking, or using illicit drugs before the age of 18.

Comorbid Disorders

Individuals with comorbid (i.e., co-occurring) mental health disorders such as depression, anxiety, attention-deficit/hyperactivity disorder (ADHD) or post-traumatic stress disorder are more likely to develop substance use disorders. The NIDA cites early aggressive behavior as a risk factor for substance use. A study by the National Bureau of Economic Research found that there is a “definite connection between mental illness and the use of addictive substances” and a majority of mental health patients participate in the use of these substances: 38% alcohol, 44% cocaine, and 40% cigarettes.

Sociocultural Factors

Due to cultural variations, the proportion of individuals who develop a drug or behavioral addiction within a specified time period (i.e., the prevalence) varies over time, by country, and across national population demographics (e.g., by age group, socioeconomic status (SES), etc.)

Internationally, the United States and Eastern Europe contain the countries with the highest substance abuse disorder occurrence (5%-6%). Africa, Asia, and the Middle East contain countries with the lowest worldwide occurrence (1%-2%). Across the globe, those that tended to have a higher prevalence of substance dependence were in their twenties, unemployed, and male. The National Survey on Drug Use and Health (NSDUH) reports on substance dependence/abuse rates in various population demographics across the United States. When surveying populations based on race and ethnicity in those ages 12 and older, it was observed that American Indian/Alaskan Natives were among the highest rates and Asians were among the lowest rates in comparison to other racial/ethnic groups.

When surveying populations based on gender in those ages 12 and older, it was observed that males had a higher substance dependence rate than females. However, the difference in the rates are not apparent until after age 17. Drug and Alcohol Dependence reports that older adults abuse drugs including alcohol at a rate of 15–20%. It’s estimated that 52 million Americans beyond 12 years old have abused a substance.

Alcohol dependence or abuse rates were shown to have no correspondence with any person’s education level when populations were surveyed in varying degrees of education from ages 26 and older. However, when it came to illicit drug use, there was a correlation in which those that graduated from college had the lowest rates. Furthermore, dependence rates were greater in unemployed populations ages 18 and older and in metropolitan-residing populations ages 12 and older.

The National Opinion Research Center at the University of Chicago reported an analysis on disparities within admissions for substance abuse treatment in the Appalachian region, which comprises 13 states and 410 counties in the eastern part of the United States. While their findings for most demographic categories were similar to the national findings by NSDUH, they had different results for racial/ethnic groups that varied by sub-regions. Overall, Whites were the demographic with the largest admission rate (83%), while Alaskan Native, American Indian, Pacific Islander, and Asian populations had the lowest admissions (1.8%).

Alcohol and Drug Abuse Around the World

In Asia, the prevalence of alcohol dependence is not as high as is seen in other regions. Many Asians (30% to 50% of people of Chinese, Japanese, and Korean ancestry) have at least one ALDH2*2 allele, which may cause alcohol flush reaction, or a sensitivity to alcohol that causes flushes or blotches on the body after alcoholic consumption. In Europe in 2015, the estimated prevalence among the adult population was 18.4% for heavy episodic alcohol use (in the past 30 days); 15.2% for daily tobacco smoking; and 3.8, 0.77, 0.37 and 0.35% in 2017 for cannabis, amphetamine, opioid, and cocaine use, respectively. The mortality rates for alcohol and illicit drugs were highest in Eastern Europe.

Figure 2. Alcohol consumption throughout the world.  Hannah Ritchie (2018) – “Alcohol Consumption”. Published online at OurWorldInData.org. Retrieved from: ‘https://ourworldindata.org/alcohol-consumption’ [Online Resource]

Figure 3. Alcohol use disorder around the world is estimated to affect around 1.4% of the population. For most countries, the rate of prevalence is around 1 or 2%, but some countries, such as Russia, Greenland, and Brazil, have higher prevalence rates.  Hannah Ritchie (2019) – “Drug Use”. Published online at OurWorldInData.org. Retrieved from: ‘https://ourworldindata.org/drug-use’ [Online Resource]

The realities of opioid use and abuse in Latin America may be deceptive if observations are limited to epidemiological findings. In the United Nations Office on Drugs and Crime report, although South America produced 3% of the world’s morphine and heroin and 0.01% of its opium, the prevalence of use is uneven. According to the Inter-American Commission on Drug Abuse Control, consumption of heroin is low in most Latin American countries, although Colombia is the area’s largest opium producer. Mexico, because of its border with the United States, has the highest incidence of use.

Figure 4. While alcohol abuse is more common in Russia and Eastern Europe, the United States has the highest percentage of the population suffering from drug use disorders.  Hannah Ritchie (2019) – “Drug Use”. Published online at OurWorldInData.org. Retrieved from: ‘https://ourworldindata.org/drug-use’ [Online Resource]

Figure 5. Map showing the share of the population with alcohol or drug use disorders. Hannah Ritchie (2019) – “Drug Use”. Published online at OurWorldInData.org. Retrieved from: ‘https://ourworldindata.org/drug-use’ [Online Resource]

United States

Figure 6. One-third of inpatient hospital costs and 20% of all deaths in the United States every year are the result of untreated addictions and risky substance use.

Based upon representative samples of the U.S. youth population in 2011, the lifetime prevalence of addictions to alcohol and illicit drugs has been estimated to be approximately 8% and 2%-3%, respectively. Based upon representative samples of the U.S. adult population in 2011, the 12-month prevalence of alcohol and illicit drug addictions were estimated at roughly 12% and 2%-3% respectively. The lifetime prevalence of prescription drug addictions is currently around 4.7%.

As of 2016, about 22 million people in the United States need treatment for an addiction to alcohol, nicotine, or other drugs. Only about 10%, or a little over two million, receive any form of treatment, and those that do generally do not receive evidence-based care. One-third of inpatient hospital costs and 20% of all deaths in the United States every year are the result of untreated addictions and risky substance use. In spite of the massive overall economic cost to society, which is greater than the cost of diabetes and all forms of cancer combined, most doctors in the United States lack the training to effectively address drug addiction.

In 2019, opioid addiction was acknowledged as a national crisis in the United States. An article in The Washington Post stated that “America’s largest drug companies flooded the country with pain pills from 2006 through 2012, even when it became apparent that they were fueling addiction and overdoses.