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The Biological Causes of Drug Addiction

A. Tom Horvath, Ph.D., ABPP, Kaushik Misra, Ph.D., Amy K. Epner, Ph.D., and Galen Morgan Cooper, Ph.D. , edited by C. E. Zupanick, Psy.D.

So how do people get addicted to drugs anyway? The recent contributions of science and medicine during the past 50-60 years have greatly advanced our understanding of addiction. We are beginning to understand the biological forces that affect behavior (both humans and animals). Addiction is easier to understand when we consider that our biology programs us to pursue and repeat pleasurable experiences. However, we are not slaves to our biology. The unrestrained pursuit of pleasure represents a type of developmental immaturity as depicted in the classic story of Peter Pan. Therefore, psychological, socio-cultural, and spiritual factors influence whether we mature beyond our biological limitations. Until fairly recently, people with addictive disorders such as drug addiction were viewed as selfish, weak-willed folks. They seemed to behave badly without regard for themselves, or others. People with addictive problems will tell you, willpower is not enough. As we will soon see, our biological make-up explains why this is so.

Advancements in neurobiological research have changed the way we view addiction. Addiction is no longer limited to problematic substance use. We now know that certain activities can also be addictive (sex, gambling). This is because addiction is a problem of brain functioning. We become addicted to the chemicals our brain releases, not the substance or activity that causes this release. Our genetics greatly determine our brain functioning.

The American Society of Addictions Medicine (ASAM) is the nation's largest professional society of addiction physicians. ASAM is dedicated to treating and preventing addiction. ASAM recently released (August 15, 2011) a new definition of addiction. It states that genetics account for about 50% of the likelihood that someone will develop an addiction . This ASAM definition of addiction describes addiction as a "chronic disease of the brain." This is quite different from our own definition.

It remains controversial whether or not we should reduce addiction to a "chronic disease of the brain." Nevertheless, there is strong evidence to suggest a genetic component to addiction.   Clearly, addiction does not develop merely because someone is weak-willed.  Addicted persons do not choose their genetics. Therefore, they do not control whether they are at risk for developing an addiction.

Although our biological make-up is a powerful influence, we are not slaves to our biology.  In other words, our biology does not completely drive our behavior.  People are certainly capable of choosing recovery over addiction.  This makes addictive disorders very similar to other diseases and disorders.  Many health problems require lifestyle changes to restore health.  For instance, people with diabetes must regularly check blood sugar levels and count carbohydrates.   People with heart disease must choose a healthier diet and an exercise program.  Obviously, these folks did not choose to have these health challenges. However, but they most certainly do choose how to handle them.  The same is true for people with addictions such as drug addiction.

The brain is the most dynamic and complex organ in our bodies.  The brain's proper functioning ensures our very survival.  When our brains functions well, we are constantly adapting to our environment (our surroundings).  Ironically, it is the brain's ability to be so adaptive that contributes to the formation of addiction.   Addiction causes changes to the brain in at least four fundamental ways:

 1. Alcoholism causes changes to the brain's natural balance (homeostasis).
 2. Alcoholism alters brain chemistry.
 3. Alcoholism changes the brain's communication patterns.
 4. Alcoholism causes changes to brain structures and their functioning.

The addictions topic center explains these ways that addiction affects the brain in much greater detail.

Many of the symptoms we commonly associate with addiction are due to these changes in the brain:

1. Changes to the brain's cerebral cortex are associated with impaired decision-making, impulsivity, and compulsivity.  These changes make it more likely that you will use drugs, or have difficulty resisting the urge to use.  

2. The brain's reward system is responsible for drug-seeking, and cravings.  From an evolutionary point of view, the brain's reward system ensures the survival of our species.  We are more likely to repeat behaviors that are pleasurable (such as eating and sex).  Unfortunately, addictions hijack this healthy function.  People become addicted because they experience drug effects as pleasurable.  This function of the brain makes relapse more likely even though people have good intentions to stop using.

3. The brain's amygdala is associated with memory and emotion.  Certain "cues" are stored as positive or negative memories.  For example, let's suppose someone always comes home and uses marijuana.  Coming home, and the time (finishing work) now serve as cues to use because these cues are stored as a positive memory associated with marijuana.  When someone tries to stop using, these cues serve as powerful motivators to use despite someone's best intentions to refrain from use.  Likewise, people often describe drug addiction as a habit, and one that is difficult to break.  When people attempt to discontinue an addiction like drug use, they can experience withdrawal.  The memory of withdrawal is such an unpleasant experience that it serves as a powerful motivator (or cue) to resume the addictive behavior to avoid the unpleasant experience.  Eventually, the relief from withdrawal (by resuming use) becomes pleasurable in and of itself.  These relapse triggers are due to the amygdala's effect on memory and emotions.  

4. Alcohol's effect on the brain's hypothalamus creates problems with stress regulation.  People often use drugs to relieve stress.  Since withdrawal from drug use is itself stressful, this creates a vicious cycle.  Stopping drug use creates stress, but the use of drugs diminished the brain's ability to regulate stress.