The Biology of Addiction

Updated: May 23, 2020

Addiction has a profound impact on the brain’s neurobiology. In the same way that heart disease interferes with the normal functioning of the cardiovascular system, addiction hijacks the areas of the brain involved in reward, motivation, and memory. This results in loss of control over the use of an addictive substance or behavior despite the negative consequences it’s causing.

Reinforcing Rewards

All addictive substances act on the nucleus accumbens, which is known as the pleasure center in the brain. When a drug like alcohol is consumed, it floods the nucleus accumbens with dopamine, a feel-good neurotransmitter. Recent research suggests that dopamine isn’t just involved in the feeling of satisfaction, it motivates or propels us to return to the same behavior. Dopamine is responsible for the feeling of ‘wanting’ or seeking out an addictive substance again.

After dopamine is released, other parts of our limbic system also play a role in reinforcing addiction. The hippocampus stores memories of the pleasure we received from the substance or behavior. Our amygdala, which is the emotional coder of memories, then creates a conditioned response when we think or are reminded of the addictive substance. For example, when I see a picture of a chocolate cake, I will associate it with both a pleasant memory and emotional experience. This is involved in the formation of triggers or environmental cues that initiate cravings to use an addictive substance.

Tolerance and Dependence

Over time, the repeated use of an addictive substance results in a higher tolerance. This means we need a greater amount to achieve the same rewards. Tolerance develops in addiction because our brain starts producing less of the feel-good neurotransmitters that are released when we’re using our substance of choice. That’s the reason most addictions result in depression, anxiety, and irritability in the days following use. Our brain has become depleted of dopamine and other neurotransmitters responsible for regulating our mood.

As tolerance increases, individuals regularly consuming the substance become physically dependent. Physical dependence implies there are unpleasant withdrawal symptoms when stopping use. And the greater the consumption and duration of use, the worse the withdrawal. When physical dependence and addiction begin to take hold, users may find that the substance or behavior is no longer bringing them much enjoyment at all. Unfortunately, because of pathways created in our hippocampus and amygdala, we continue to associate our addiction with a pleasurable experience, even when it delivers diminishing rewards and starts to cause problems.

Addiction and Recovery

Individuals struggling with addiction have an impaired ability to stop not only because of loss of control of our reward system, but also the part of our brain involved in decision-making and planning. Addiction impairs the prefrontal cortex, which is responsible for executive function. When the prefrontal cortex is not doing its job, individuals have more difficulty delaying rewards and self-monitoring. That contributes to relapse.

In the last decade, we’ve learned it’s not just alcohol or substances that can cause addiction. Research shows that other pleasurable activities such as gambling, shopping, gaming, and sex also result in neurobiological changes in the brain. Regardless of whether it’s a substance or behavior, addiction is recognized as a chronic disease by the medical community that has a biological, psychological, and social impact. Just like diabetes or cancer, addiction results in abnormal functioning of the brain (known as pathophysiology), produces foreseeable signs and symptoms, and follows a predictable course that can be treated.

Sources: How Addiction Hijacks the Brain. (2011). Harvard Medical School. Available at

Koob GF, et al. (2010). Neurocircuitry of Addiction. Neuropsychopharmacology. Vol. 35, No. 1, pp. 217–38.

National Institute on Drug Abuse. (2010). Drugs, Brains, and Behavior: The Science of Addiction. National Institutes of Health.

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