The Science Behind Heroin Addiction

To understand the science behind heroin abuse, we must first look at exactly what heroin is, how it affects the body, and the side effects behind the addiction.

Heroin addiction is a very complex disease defined as a chronic, relapsing disorder characterized by continued use despite harmful consequences, compulsive drug-seeking behavior, and long-lasting changes in the brain. Addiction is a medical and mental illness caused by repeated misuse of drugs or alcohol, such as heroin.

The Science Behind Heroin Addiction

What Is Heroin and How Does It Affect the Body?

To understand the science behind heroin abuse, we must first look at what heroin is and how it affects the body. Heroin is a highly addictive, illegal opioid drug that is processed from morphine, which is a naturally occurring substance; it is extracted from the seeds of the poppy plant. Heroin, like all other opioids, binds to the opioid receptors in the brain and depresses the central nervous system. When someone takes a dose of heroin, it causes an intense euphoric rush and produces a sense of calm and relaxation.

According to the National Institute on Drug Abuse:

Nearly all addictive drugs directly or indirectly target the brain’s reward system by flooding the circuit with dopamine. Dopamine is a neurotransmitter present in regions of the brain that regulate movement, emotion, cognition, motivation, and reinforcement of rewarding behaviors. When activated at normal levels, this system rewards our natural behaviors. Overstimulating the system with drugs, however, produces effects which strongly reinforce the behavior of drug use, teaching the person to repeat it. (NIDA)

Heroin is one of the most addictive drugs due to the rush and extreme euphoria it produces. The extreme euphoria from heroin abuse is caused by a rush of dopamine and other neurotransmitters flooding the brain.

Why Can’t You Stop Using Heroin?

So, now that we know exactly what heroin is and how it affects the body, we may wonder how someone gets to the point where they can’t stop using it. Let’s take, for instance, a person with a mental illness, such as depression or anxiety, who is not being treated. This individual suffers from an injury or illness that leads them to seek treatment from their doctor. They have been prescribed an opioid medication and started taking it as prescribed.

Suddenly, they are no longer hurting, and their depression and anxiety have disappeared. They continue taking the medication long after the pain from their injury is gone because they no longer feel depressed or anxious; this is self-medicating. The behavior continues, and they realize they have become physically dependent on the opioid; if they stop, they will start suffering from debilitating withdrawal symptoms.

Heroin Creates Painful Withdrawal Symptoms

Now the individual realizes that they feel so much better when they are taking the opioid and that if they stop, they are going to be very sick. So they go back to the doctor to get another prescription, and the doctor won’t give them one. They may also try other doctors but are still unsuccessful; this individual is desperate. They don’t want to suffer from the withdrawal and can’t get a prescription, so they turn to heroin. It’s much cheaper and easily accessible.

Heroin prevents them from going into withdrawal, and they get this intense euphoric rush. The dopamine receptors in the brain are overstimulated, and they feel amazing. This individual is at a point where they are willing to do anything to get the drug, even if it means committing a crime, stealing, or lying. They can no longer work or lead a productive life. They are now exhibiting compulsive drug-seeking behavior despite any negative consequences; they are in full-blown addiction.

What Is Heroin Use Disorder?

The DSM classifies heroin addiction as a “substance use disorder.” There are 11 diagnostic criteria to determine whether a person has a mild, moderate, or severe substance use disorder. If an individual has two or three of the criteria, they are considered “mild.” If they have four or five, they are considered to have “moderate” substance use disorder. Six or more criteria are classified as “severe” substance use disorder.

The National Institute on Drug Abuse lists these 11 criteria for substance use disorders.

  • The substance is often taken in larger amounts or over a longer period than was intended.
  • There is a persistent desire or unsuccessful effort to cut down or control the use of the substance.
  • Much time is spent on activities necessary to obtain the substance, use it, or recover from its effects.
  • Craving, or a strong desire or urge to use the substance, occurs.
  • Recurrent substance use fails to fulfill major role obligations at work, school, or home.
  • Use of the substance continues despite having persistent or recurrent social or interpersonal problems caused or exacerbated by the effects of its use.
  • Important social, occupational, or recreational activities are given up or reduced because of substance use.
  • Substance use is recurrent in situations where it is physically hazardous.
  • Substance use is continued despite knowledge of a persistent or recurrent physical or psychological problem that is likely to have been caused or exacerbated by the substance.
  • Tolerance, as defined by either of the following:
    • A need for markedly increased amounts of the substance to achieve intoxication or desired effect
    • A markedly diminished effect with continued use of the same amount of the substance.
  • Withdrawal, as manifested by either of the following:
    • The characteristic withdrawal syndrome for that substance (as specified in the DSM-5 for each substance).
    • A substance (or a closely related substance) is used to relieve or avoid withdrawal symptoms.

Many people will never understand the science behind addiction. I have heard so many people say, “it is a choice.” Well, it may be a choice at first, but a person loses control with continued use. The brain starts to change, especially in the areas responsible for memory, critical judgment, learning, decision-making, and behavior control. Brain imaging studies have been done on addicts and have shown these changes. Addiction or substance use disorder is a disease, and just like cancer, diabetes, or any other medical illness, it requires treatment to get better.

Evidence-Based Treatment for Heroin Abuse

If you or someone you love is struggling with an addiction, our addiction specialists are available around the clock to assist you. Absolute Awakenings follows an evidence-based approach to treating substance abuse disorders. We are committed to providing long-term recovery for those struggling with addiction. Recovery is not a one-size-fits-all approach, so every person that walks through our doors is provided with a unique and individualized experience. Our recovery specialists are waiting to assist you. Call us today!


  1. Huecker MR, Koutsothanasis GA, Abbasy MSU, Marraffa J. Heroin. In: StatPearls. StatPearls Publishing; 2022. Accessed January 16, 2023.
  2. The Science of Drug Use and Addiction: The Basics. Accessed January 16, 2023.
  3. National Institute on Drug Abuse. What effects does heroin have on the body? National Institute on Drug Abuse. Published June 2018. Accessed January 16, 2023.
  4. Hartney E. The Symptoms Used to Diagnose Substance Use Disorders. Verywell Mind. Published August 25, 2022. Accessed January 16, 2023.
Amanda Stevens, BS

Amanda Stevens, BS

Amanda is a prolific medical content writer specializing in eating disorders and addiction treatment. She graduated Magnum Cum Laude from Purdue University with a B.S. in Social Work. As a person in recovery from disordered eating, she is passionate about seeing people heal and transform. She writes for popular treatment centers such as Infinite RecoveryAscendant NY, The Heights Treatment, New Waters RecoveryGallus DetoxRecovery UnpluggedOcean RecoveryRefresh Recovery and adolescent mental health treatment center BasePoint Academy. In her spare time she loves learning about health, nutrition, meditation, spiritual practices, and enjoys being the a mother of a beautiful daughter.

Last medically reviewed January 16, 2023