Science of addiction

DEFINITION: Neuroscientists define addiction as a chronic, relapsing brain disease. Addiction is considered a brain disease because it alters the brain’s structure and chemistry in fundamental, long-lasting ways.

Stages of Addiction

There are three related stages in addiction: acute drug effect, transition to addiction, and end-stage addiction. In the early stage, the individual experiences the rewarding effects of the addictive drug. Dopamine is the key brain chemical involved at this stage. In the second stage, the individual transitions from recreational use to addiction. Glutamine is the key brain chemical involved at this stage. At the third and final stage, the individual experiences a strong urge to obtain the addictive drug loses control of the drug-seeking desire, and experiences diminished pleasure after using the addictive drug, requiring larger and more frequent dosing to achieve the same initial effects.

Although the science of addiction is still not fully understood, scientists have worked out two major pathways in the brain responsible for addiction. First, there is the mesolimbic pathway mediated by dopamine. Second, the prefrontal cortex, the decision-making center, is responsible for controlling any inappropriate reward responses. Drug addiction can lead to physical changes in these pathways.

Neuroimaging techniques, such as PET scans and MRIs, have documented changes in the size and shape of nerve cells in the brains of individuals with addictions. Networks of nerve cells determine a person’s feelings and behavior. Drugs influence behavior by transforming the way these networks function.

The Dopamine Connection

The biological link among all addictions is dopamine, though some research suggests dopamine plays the central role in some addictions (such as stimulants) and a minor role in others. This brain chemical is released during pleasurable activities, ranging from sex to eating, to more detrimental behaviors such as drinking and taking drugs. A powerful drug like crack cocaine elevates dopamine levels much faster than normal pleasurable activities. It creates the classic drug-induced feelings of exhilaration and power. In a landmark 1950s experiment, scientists stimulated rodent brains and found that the animals kept returning to the place where they received the stimulation.

Coming down from a drug high is caused by a decrease in dopamine levels. If a person’s brain cells produce excessive dopamine on a regular basis, such as through repeated exposure to an addictive substance, the cells adjust to the unnaturally elevated levels of dopamine in the brain and begin to produce less dopamine. Over time, the individuals need drugs just to stimulate dopamine to normal levels. They become trapped in a cycle of cravings and addiction to avoid withdrawal symptoms and depression. It is believed that once a person crosses the line into addiction, the brain is so changed that they can no longer control their behavior.

This transformation helps to explain why it is so difficult to break an addiction. Cravings are more significant than physical withdrawal in keeping an individual with an addiction using. Drugs like cocaine and methamphetamine, unlike heroin and alcohol, do not produce intense physical withdrawal symptoms, but they do produce powerful psychological symptoms, including overwhelming cravings. These cravings can be aroused by external or internal stimuli that are as innocuous as walking by a pub or feeling sad.

An Addictive Personality?

Although the influence of dopamine and other elements of brain chemistry on addiction is widely accepted by scientists, not all people react to drugs or addictive behaviors the same way, leading researchers to propose additional factors in the process of addiction. Many addiction professionals believe that addiction stems from a combination of biological, psychological, and environmental factors. Many support groups for addiction recovery also follow this belief. For example, Alcoholics Anonymous describes alcoholism as a physical, emotional, and spiritual disease.

The progression to addiction can develop in this way: A person may have a genetic or biological predisposition to an addiction. If they grow up in a family and environment without addiction or stress, they may never begin casual drug use. However, if the person grows up in a stressful environment where substance abuse is common and encounters more stressors over time, they may begin casual use and, because of the permanent changes in the brain caused by repeated drug use, they become addicted.

Although the science of addiction remains controversial, research into a genetic component of addiction is ongoing. Some scientists assert that genes account for 40 to 60 percent of an individual's risk of developing an addiction. Research has identified several "addiction genes" that are associated with particular substances. For example, the genes CUL3, PDE4B, and PTGER3 are associated with smoking and alcohol use, and HIST1H2BD is associated with cocaine use. From a social standpoint, children of individuals addicted to alcohol have been shown to be at a higher risk of becoming addicted to alcohol themselves than children of individuals who do not abuse alcohol, though it is difficult to determine the exact interplay between biology and environment. Scientists are also studying whether some individuals are born with inadequate endorphins, the brain chemicals that regulate stress, predisposing them to addictive behaviors.

Treatments

Since the 1960s, methadone has been used to ease withdrawal symptoms by normalizing brain chemistry, limiting cravings, and blocking the effects of heroin and narcotics. Naltrexone is another drug commonly used for alcohol and narcotics addiction, while acamprosate and disulfiram are primarily used in cases of alcohol addiction. Another drug, buprenorphine, is another alternative to methadone in treating narcotic addictions. Useful for detoxification, the synthetic opioid buprenorphine (usually combined with naltrexone) can also be used for maintenance therapy. Buprenorphine can be prescribed by psychiatrists and other doctors who have received special training. Methadone, in contrast, can only be dispensed from a specially licensed clinic.

In addition to medications that aid individuals in active addiction, opioid overdose reversal medications (OORMs) became critical life-saving tools amid the opioid crisis of the twenty-first century, including Naloxone (Narcan, Evzio) and nalmefene (Revex). The US Food and Drug Administration approved the first over-the-counter OORM in 2023, a nalmefene hydrochloride nasal spray.

It is unlikely that a magic pill will be found that “cures” addiction. On the other hand, aerobic exercise offers a simple and natural way to help combat addiction. During aerobic exercise, dopamine levels increase in the areas of the brain involved with addiction, and feelings of depression and anxiety decrease.

Bibliography

DiClemente, Carlo C. Addiction and Change: How Addictions Develop and Addicted People Recover. 2nd ed., New York City, Guilford Press, 2018.

Erickson, Carlton. The Science of Addiction: From Neurobiology to Treatment. 2nd ed., New York City, W. W. Norton, 2018.

Hart, Carl L., Charles Ksir, and Oakley Ray. Drugs, Society and Human Behavior. 18th ed. New York City, McGraw-Hill-Hill, 2022.

Miller, Shannon C., et al. The ASAM Principles of Addiction Medicine. 7th ed., New York City, Wolters Kluwer, 2024.

Nutt, David J., et al. "The Dopamine Theory of Addiction: 40 Years of High and Lows." Nature Reviews Neuroscience, vol. 16, 2015, pp. 305–312.

Schaler, Jeffrey. Addiction Is a Choice. Peru, Il: Chicago, Carus Publishing Company, 2000.

Volkow, Dr. Nora D. "How Science Has Revolutionized the Understanding of Drug Addiction." National Institute on Drug Abuse, July 2020, nida.nih.gov/publications/drugs-brains-behavior-science-addiction/preface. Accessed 2 Dec. 2022.