Triggr Health
Neuroscience of Addiction

The Science of Addiction

A substance use disorder is a physiological disease, not a personal failing or weakness.

“You just have to use your willpower”

“Just muscle through it”

“You’re not strong enough to quit”

"Why can't you just stop?

If you are struggling with a substance use disorder, you have no doubt heard these sentiments from someone else or thought them to yourself. Substance use disorders are often incorrectly blamed on a lack of willpower, laziness, or a moral failing, but the truth is that it is a disease, like cancer or diabetes, and behavioral factors are only one component of what causes them Environmental and genetic factors also play a big role, and like these other ailments, they are very, very hard to cure.

Learning about the basic neuroscience of addiction can help you better understand why this is the case. Addiction is complicated, but by breaking it down into its constituent parts, you can better understand why you or a loved one became addicted in the first place, why cravings happen , and why withdrawals happen. Ultimately, studying these areas will help you understand that an addiction is not a personal or moral failing, but a physiological disease.

Genetic Factors

Written in our genetic script are genes, or sequences of our DNA that code for biological traits or functions. There is no single addiction gene but there are a number of genes that may make you more predisposed to addiction than another person. These genes are hereditary, so if someone in your family suffers from a substance use disorder, you might be predisposed to one as well.

Another risk factor that may contribute to SUD genetic predisposition is having a preexisting mental health disorder, such as depression, anxiety, eating disorders, or other psychiatric condition.

It is thought that at least half of a person’s susceptibility to addiction can be attributed to genetics (the other half being environmental factors and behavioral factors). However, it is important to note that neither the presence of these genes nor addiction in the family means that addiction is a biological destiny. It does mean the odds are greater, but it is certainly not an inevitability.

Environmental Factors

The world around us is our environment and it affects the way our genetic script gets read by our bodies. In this sense, environmental factors can also play a large role in someone’s susceptibility to addiction.

Some of these environmental risk factors include experiencing physical, sexual, or emotional trauma of some kind, witnessing substance use in your family and/or peers, having access to addictive substances, being exposed to pop culture references to substance use at a young age, and starting alcohol or drug use at a young age. Like the genetic factors, none of these mean that addiction is predestined or written in stone.

Reward Pathway

Think about a time when you felt really good. Maybe you just received praise at work, ate something super delicious, hugged a person you love -- in all of these cases, you felt pleasure because the reward pathway in your brain was activated.

What does it mean for a reward pathway to be activated? A pleasurable stimulus like a hug, delicious food, or praise causes the brain to release a neurotransmitter (a messenger molecule that activates nerve cells or “neurons” in the brain) called dopamine. Dopamine is responsible for creating feelings of euphoria.

When dopamine is released in response to this pleasurable stimulus, it activates a number of structures in your brain that are associated with decision-making, motor control, memory-making and euphoria. The activation of these structures together causes your brain to say “That was great! Let’s do it again! I want more!” This is called the reward pathway.

At the same time that dopamine levels are going up and increasing feelings of euphoria, a different neurotransmitter, called serotonin, is decreasing. Serotonin is responsible for feelings of satiation, so the more you activate this reward pathway, the less satisfied you feel, instead of more satisfied.

In this state, the brain also tries to remember everything about this situation so that it can recreate and find this pleasure again in the future. The brain remembers that in this environment with these people at this time of day in the past it felt really good, and so in response to those environmental cues (aka “triggers”) at a later time, it expects the same euphoria it felt before and sparks use-seeking behavior in order to do so. That’s why triggers are so strong.

Addictive substances activate this exact same reward pathway, but they are far more potent than a hug, delicious food, or praise. So, the drive to seek out this extremely high level of pleasure is incredibly strong and difficult to resist with sheer willpower or strength alone.


Let’s say you’ve just had a delicious brownie which activated your reward pathway: you feel euphoric and you want more. After a little while, though, that brownie euphoria subsides and you go back to homeostasis, or baseline normalcy.

With an addictive substance, however, that reward pathway is inundated by dopamine. Constant drug use and overstimulation of your reward pathway makes it very difficult for your brain to return to that homeostasis, so your brain compensates: it increases the number of dopamine receptors in order to handle the increased amount of dopamine.

Now, because there are more dopamine receptors than there were previously, the same amount of drug has less of an effect. This is what leads to drug tolerance. A greater amount of the drug is necessary to produce the same level of euphoria first experienced, so you must continually up the dosage in order to feel the same effect.


After sustained drug use, not only is tolerance for the drug increased, but the baseline or state of normalcy itself is also changed. You may find yourself needing a certain amount of the substance just to feel normal, not even high or euphoric. Your body is always trying to reach and maintain its homeostasis, and a craving is what happens when your brain has adjusted to a certain amount of drugs -- its new normal -- and then it is suddenly depleted. The brain is expressing desire to reach homeostasis again, but a different homeostasis than that of a non-addicted brain.


Over time, not only does the brain increase the number of dopamine receptors it has available, but it also might get so used to external drugs providing dopamine that it stops creating its own dopamine entirely. It relies entirely on those drugs to provide a dopamine reward.

In this scenario, if the drugs are stopped cold-turkey, your body is craving and it is unable to produce its own dopamine. The brain can’t reach its normal state, and this can lead to feelings of depression, anxiety, shakiness, sweating, and headaches (though the exact symptoms can vary depending on what kind of substance one is withdrawing from).

Bottom Line: The science of addiction can be complex and confusing. The main takeaways for someone thinking about changing their drug and/or alcohol habits are as follows:

  • Moderation or quitting is hard because substance use disorders physiologically change the brain. It is not laziness, lack of willpower, or a moral failing; the brain has come to expect a certain amount of the substance and has optimized to seek that substance out when it is depleted.
  • Quitting cold-turkey is not only unpleasant, for certain drugs it can sometimes be dangerous or even life-threatening. Your brain and body have fully adapted and changed to handle the drug. Stopping cold-turkey throws that finely-tuned machine out of whack.
  • MAT or tapering can help ease the cravings and withdrawal symptoms, making moderation or quitting more likely and sustainable!


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