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Understanding the Science of Addiction

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Clinically Reviewed by:
Lindsey Rae Ackerman, LMFT

Written by:
Alex Salman, MPH on March 13, 2024

Addiction is a concept that is deceptively difficult to define. It’s a multifaceted phenomenon that encompasses biological, psychological, and social elements, making it challenging to capture within a single framework.[1] Understanding the science of addiction reveals effective treatment approaches and ways to combat its far-reaching effects.

At its core, addiction involves a compulsive urge to engage in a behavior or consume a substance despite ongoing negative consequences. However, the intricate interplay between genetics, environment, and individual psychology adds several layers of complexity.[1]

In today’s blog, Clear Behavior Health will explore both the physiological underpinnings of addiction and the profound implications it holds for individuals, families, and communities alike.

How is Addiction Defined?

Addiction can be defined as a chronic, relapsing, and treatable condition characterized by compulsive drug seeking, continued use, and an inability to control or stop using a substance or engaging in a behavior despite negative consequences.

Addiction can involve substances such as drugs (e.g., alcohol, opioids, cocaine) or behaviors such as gambling or excessive internet use. It often has detrimental effects on various aspects of a person’s life, including their physical health, mental well-being, relationships, work, and finances.[2]

What Does it Mean to Say Addiction is a Relapsing Condition?

Describing addiction as a disorder of relapse refers to the tendency for people struggling with addiction to experience repeated episodes of returning to substance use or engaging in addictive behaviors, even after periods of abstinence or successful treatment. This concept of addiction as a relapsing brain disorder underscores the chronic and often long-term nature of addiction, highlighting that it is not simply a matter of willpower but rather a complex neurological and psychological condition.[3]

Why Do People Become Addicted?

People become addicted due to a combination of genetic, environmental, and psychological factors:

  • Genetics: Genetic predisposition can play a significant role in addiction. Some people may have a genetic vulnerability that makes them more susceptible to developing addiction when exposed to certain substances or behaviors. Genetic factors can influence how the brain responds to drugs or other addictive stimuli, affecting an individual’s likelihood of developing an addiction.
  • Brain chemistry: Addiction involves changes in the brain’s reward system and other neural circuits. Substances can hijack the brain’s natural reward pathways, leading to the release of neurotransmitters like dopamine, which are associated with pleasure and reinforcement. Over time, repeated substance use or engaging in addictive behaviors can alter brain chemistry, leading to tolerance, dependence, and craving.
  • Environmental factors: Environmental influences, such as upbringing, peer pressure, stress, trauma, and access to addictive substances or behaviors, can also play a significant role in addiction. Early exposure to substance abuse or addictive behaviors in the family or social circle can increase the risk of developing addiction later in life.
  • Psychological factors: Psychological factors, including personality traits, mental health disorders, and coping mechanisms, can contribute to addiction as well. Individuals may use substances or engage in addictive behaviors as a way to cope with stress, trauma, anxiety, depression, or other emotional issues. Furthermore, certain personality traits, such as impulsivity, sensation-seeking, or a propensity for risk-taking, can increase the likelihood to seek drugs and develop an addiction.
  • Social and cultural influences: Cultural norms, societal attitudes toward substance use, and the availability of addictive substances or behaviors can also influence addiction. Social acceptance of substance use or certain behaviors may normalize addictive behaviors and make it easier for individuals to develop and maintain addictive habits.[4]

What is a Substance Use Disorder, and How is it Defined?

A substance use disorder (SUD) is a clinical term used to describe a problematic pattern of substance use that leads to significant impairment or distress. It encompasses a range of behaviors related to the recurrent use of substances such as alcohol, opioids, cocaine, cannabis, or other drugs.

According to the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) , a substance use disorder is characterized by a cluster of symptoms that indicate impaired control over substance use, social impairment, risky use, and select pharmacological criteria (such as tolerance and withdrawal). The severity of the disorder can be classified as mild, moderate, or severe, depending on the number of symptoms present:

  • Impaired Control: This criterion involves unsuccessful efforts to cut down or control substance use, spending a significant amount of time obtaining, using, or recovering from the effects of the substance, and experiencing strong cravings for the substance.
  • Social Impairment: Social impairment includes failure to fulfill major role obligations at work, school, or home due to substance use; continued substance use despite social or interpersonal problems caused or exacerbated by substance use; and withdrawal from social, occupational, or recreational activities because of substance use.
  • Risky Use: This criterion involves using substances in situations where it is physically hazardous, such as driving under the influence, or continuing substance use despite knowledge of persistent or recurrent physical or psychological problems caused or exacerbated by the substance.
  • Pharmacological Criteria: Pharmacological criteria include the development of tolerance, defined as needing increased amounts of the substance to achieve the desired effect, and experiencing withdrawal symptoms when substance use is discontinued or reduced.

To receive a diagnosis of substance use disorder, an individual must meet specific criteria outlined in the DSM-5, including the presence of at least two of the above criteria within the past year. The severity of the disorder is determined by the number of symptoms present: 2-3 symptoms indicate a mild disorder, 4-5 symptoms indicate a moderate disorder, and 6 or more symptoms indicate a severe disorder.[5]

How Substance Use Affects the Brain

Substance use can have profound effects on the human brain, impacting neurotransmitter systems, altering neural pathways, and ultimately leading to short-term and long-term changes in brain function.

Neurotransmitters are chemical messengers in the brain that play a critical role in communication between neurons. When it comes to the brain, drugs and certain substances can directly or indirectly affect neurotransmitter levels, leading to various effects on mood, behavior, and cognition.[6]

Some of the key neurotransmitter systems affected by substance use include:


Many drugs of abuse, including cocaine, amphetamines, opioids, and alcohol, directly or indirectly increase dopamine levels in the brain’s reward pathway. Dopamine is associated with feelings of pleasure and reinforcement, and its release reinforces substance-seeking behaviors.[7]


Drugs like MDMA (ecstasy) and hallucinogens such as LSD and psilocybin affect serotonin levels in the brain, leading to altered mood, perception, and cognition. Changes in serotonin function can contribute to the euphoric and hallucinogenic effects of these substances.[8]

Gamma-aminobutyric acid (GABA)

GABA is an inhibitory neurotransmitter that helps regulate neuronal excitability. Drugs such as alcohol and benzodiazepines enhance GABAergic activity, leading to sedation, relaxation, and anxiolytic effects.[9]


Glutamate is the brain’s primary excitatory neurotransmitter involved in learning, memory, and synaptic plasticity. Many drugs of abuse—including stimulants like cocaine and methamphetamine—disrupt glutamatergic signaling, leading to neuroadaptations that contribute to addiction and cognitive impairments.[10]

The Short-Term Effects of Addiction

Substance use can produce immediate and noticeable effects on the brain, including:

  • Euphoria and pleasure: Many drugs stimulate the brain’s reward pathway, leading to feelings of euphoria and pleasure.
  • Altered perception and cognition: Hallucinogens such as LSD and cannabis can distort sensory perception, alter thought patterns, and impair judgment and decision-making.
  • Impaired motor coordination: Substances like alcohol and sedatives depress the central nervous system, leading to impaired coordination, slurred speech, and impaired reflexes.
  • Increased heart rate and blood pressure: Stimulant drugs like cocaine and amphetamines can cause tachycardia (rapid heart rate) and hypertension (high blood pressure), increasing the risk of cardiovascular complications.[11]

The Long-term Effects of Addiction

Prolonged substance use can lead to persistent changes in brain structure and function, resulting in:

  • Neuroadaptations: Chronic drug use induces neuroadaptive changes in the brain, including alterations in neurotransmitter systems, synaptic plasticity, and gene expression. These changes contribute to tolerance, dependence, and craving.
  • Cognitive deficits: Long-term substance use is associated with cognitive impairments, including deficits in attention, memory, executive function, and decision-making. These cognitive deficits can persist even after cessation of drug use and contribute to difficulties in daily functioning.
  • Increased risk of mental health disorders: Substance use disorders are often comorbid with other mental health disorders, such as depression, anxiety, and psychosis. Prolonged substance use can exacerbate existing psychiatric conditions or precipitate the onset of new ones.
  • Structural changes: Chronic drug use can lead to alterations in brain structure, including changes in gray matter volume, white matter integrity, and neuronal morphology. These structural changes may contribute to cognitive deficits and increased vulnerability to relapse.[12]

The Effects of Specific Substances on the Brain


Stimulants are a class of drugs that increase alertness, attention, and energy levels by enhancing the activity of neurotransmitters such as dopamine, norepinephrine, and serotonin in the brain. Common stimulants include cocaine and amphetamines (e.g., Adderall, methamphetamine).

  • Increased dopamine release: Stimulants directly increase dopamine levels in the brain’s reward pathway, leading to feelings of euphoria and reinforcement.
  • Enhanced alertness and attention: Stimulants enhance the activity of norepinephrine and dopamine in areas of the brain involved in attention and arousal, leading to increased alertness, focus, and concentration.
  • Elevated heart rate and blood pressure: Stimulants can cause tachycardia (rapid heart rate) and hypertension (high blood pressure), increasing the risk of cardiovascular complications such as heart attack and stroke.
  • Psychological effects: Chronic stimulant use can lead to psychological dependence, anxiety, paranoia, and psychosis, characterized by hallucinations, delusions, and disorganized thinking.[13]


Opioids are a class of drugs that act on opioid receptors in the brain and spinal cord to produce pain-relieving effects and feelings of euphoria. Prescription opioids include medications such as oxycodone (OxyContin), hydrocodone (Vicodin), and morphine, while illicit opioids include heroin and fentanyl.

  • Pain relief: Opioids bind to opioid receptors in the brain and spinal cord, reducing the perception of pain and producing analgesia.
  • Euphoria and sedation: Opioids stimulate the brain’s reward pathway, leading to feelings of euphoria, relaxation, and sedation.
  • Respiratory depression: Opioids can depress the respiratory center in the brainstem, leading to slowed breathing, respiratory depression, and potentially fatal overdose.
  • Physical dependence and withdrawal: Prolonged opioid use can lead to physical dependence, characterized by withdrawal symptoms such as nausea, vomiting, diarrhea, muscle aches, and intense drug cravings upon cessation of drug use.[14]


Marijuana, also known as cannabis or weed, contains psychoactive compounds such as tetrahydrocannabinol (THC) and cannabidiol (CBD) that act on cannabinoid receptors in the brain.

  • Euphoria and relaxation: THC binds to cannabinoid receptors in the brain’s reward pathway, leading to feelings of euphoria, relaxation, and altered sensory perception.
  • Impaired memory and cognition: Marijuana can impair short-term memory, attention, concentration, and cognitive function, particularly in individuals who begin using it during adolescence when the brain is still developing.
  • Altered perception and mood: Marijuana use can lead to altered perception of time, space, and sensory experiences, as well as changes in mood, including anxiety, paranoia, and euphoria.
  • Risk of addiction and mental health disorders: While marijuana is less addictive than other substances, some individuals may develop cannabis use disorder, characterized by dependence, tolerance, and withdrawal symptoms. Chronic marijuana use is also associated with an increased risk of mental health disorders, such as depression, anxiety, and cannabis-induced psychosis.[15]

How Does Substance Use Affect My Mental Health?

Substance use can have significant effects and adverse consequences on mental health, exacerbating existing mental health conditions and contributing to the development of new ones. The relationship between substance use and mental health is complex and bidirectional, with substance use often serving as both a cause and a consequence of mental health disorders. This often results in dual diagnosis or comorbidity issues, where individuals battle both substance use disorders and simultaneous mental health conditions. Symptoms of depression, anxiety, and psychosis are intensified by alcohol and drugs, leading to heightened distress and impairment in daily functioning.

Chronic substance use further impairs cognitive function, affecting attention, memory, executive function, and decision-making, thereby worsening symptoms and hindering interpersonal relationships. Substance use strains social ties, fostering conflict, isolation, and withdrawal, exacerbating feelings of loneliness, depression, and anxiety.

Furthermore, substance use brings about a plethora of psychosocial stressors, including financial woes, legal troubles, housing instability, and employment issues that may contribute to an addiction crisis. Addressing co-occurring substance use and mental health disorders poses unique challenges in treatment and recovery as well, with integrated approaches targeting both aspects simultaneously often becoming necessary for optimal outcomes.[16]

The Importance of Quality Addiction Treatment

Quality addiction treatment is essential for individuals seeking to overcome substance use disorders and reclaim their lives. A comprehensive continuum of care, encompassing various levels and modalities of treatment, is crucial for addressing the complex needs of individuals struggling with addiction. This approach ensures that individuals receive personalized and holistic care tailored to their unique circumstances, promoting long-term recovery and sustained well-being.

Detox and Withdrawal Management

Withdrawal management services, often the first step in addiction treatment, involve safely managing any withdrawal symptoms and addressing medical complications associated with ceasing to use. This critical phase ensures that individuals detoxify in a supervised and supportive environment, minimizing discomfort and reducing the risk of complications.

Residential Treatment

Following detoxification, residential or inpatient treatment provides a structured and immersive therapeutic environment where individuals receive intensive therapy, counseling, and support. This level of care offers a break from the triggers and stressors of everyday life, allowing individuals to focus fully on their recovery journey and develop essential coping skills.

Outpatient Programs

Partial hospitalization programs (PHPs) or day treatment programs offer a step-down level of care for individuals transitioning from residential treatment or for those who require more intensive support than outpatient services alone can provide. These programs typically offer a combination of therapy, group sessions, and educational activities during the day, with participants returning home or to a sober living environment in the evenings.

Intensive outpatient programs (IOPs) offer a flexible treatment option for individuals who require ongoing support but can maintain daily responsibilities such as work, school, or family commitments. IOPs typically involve several hours of therapy and counseling sessions per week, allowing individuals to receive structured support while gradually reintegrating into their communities.

Outpatient counseling and therapy provide ongoing support and relapse prevention strategies as individuals transition back to their daily lives. These sessions may focus on addressing underlying issues contributing to addiction, developing healthy coping skills, and rebuilding relationships.


Aftercare services also play a vital role in supporting individuals as they transition from primary treatment back into their communities. These services may include continued therapy, support groups, sober living arrangements, vocational training, and assistance with accessing community resources. Aftercare helps individuals maintain the skills and strategies learned in treatment, navigate challenges, and build a supportive network for ongoing recovery.

Full Continuum of Care

Choosing a treatment provider with a full continuum of care offers those struggling with addiction the comprehensive support and resources they need to achieve and maintain sobriety. When it comes to addiction, drugs are only part of the problem, with mental health struggles playing a significant role. Addressing both issues is vital to overall treatment success. By addressing the physical, psychological, and social aspects of addiction, quality addiction treatment empowers individuals to overcome substance use disorders and rebuild fulfilling lives.

Help and Support for Mental Health and Addiction

Clear Behavioral Health is proud to offer the highest standard in addiction care, ensuring that individuals receive personalized treatment plans tailored to their unique needs and circumstances. Reach out to us today to learn more about our home-like withdrawal management, detox and residential rehab as well as our dual diagnosis outpatient programs for ongoing support. We’re in-network with most major insurance providers, offering you or your loved one the evidence-based, co-occurring treatment you need to begin the recovery process and fulfill your potential.


  1. National Institute on Drug Abuse. (2020, July). Drug Misuse and Addiction. National Institute on Drug Abuse. on March 4, 2024
  2. American Society of Addiction Medicine. (2019, September 15). Definition of Addiction. ASAM. on March 4, 2024
  3. MacKillop, J. (2019). Is Addiction Really a Chronic Relapsing Disorder? Alcoholism: Clinical and Experimental Research, 44(1), 41–44. on March 4, 2024
  4. National Institute on Drug Abuse. (2018, June 6). Understanding Drug Use and Addiction Drug Facts. National Institute on Drug Abuse; National Institute of Health. on March 4, 2024
  5. McNeely, J., & Adam, A. (2020, October 1). Table 3, DSM-5 Diagnostic Criteria for Diagnosing and Classifying Substance Use Disorders [abc]. on March 4, 2024
  6. Cadet, J. L., Bisagno, V., & Milroy, C. M. (2013). Neuropathology of substance use disorders. Acta Neuropathologica, 127(1), 91–107. on March 4, 2024
  7. Yale Medicine. (2022, May 25). How an Addicted Brain Works. Yale Medicine. on March 4, 2024
  8. Kirby, L. G., Zeeb, F. D., & Winstanley, C. A. (2011). Contributions of serotonin in addiction vulnerability. Neuropharmacology, 61(3), 421–432. on March 4, 2024
  9. Shyu, C., Chavez, S., Boileau, I., & Le Foll, B. (2022). Quantifying GABA in Addiction: A Review of Proton Magnetic Resonance Spectroscopy Studies. Brain Sciences, 12(7), 918. on March 4, 2024
  10. Wang, W., & Li, X. (2019, October 8). A mini-review of the role of glutamate transporter in drug addiction. Frontiers. on March 4, 2024
  11. National Institute on Drug Abuse. (2019, October). What are the immediate (short-term) effects of methamphetamine misuse? National Institute on Drug Abuse. on March 4, 2024
  12. Mayo Clinic. (2022, October 4). Drug addiction (substance use disorder) – symptoms and causes. Mayo Clinic; Mayo Clinic. on March 4, 2024
  13. National Library of Medicine. (1999). Chapter 2—How Stimulants Affect the Brain and Behavior. In Substance Abuse and Mental Health Services Administration (US). on March 4, 2024
  14. Johns Hopkins Medicine. (2022, October 19). Opioids. on March 4, 2024
  15. SAMHSA. (2023, February 27). Know the Risks of Marijuana | SAMHSA – Substance Abuse and Mental Health Services Administration.; SAMHSA. on March 4, 2024
  16. National Institute of Mental Health. (2023, March). Substance use and co-occurring mental disorders. National Institute of Mental Health. on March 4, 2024

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