Substance Addiction: Tolerance and Withdrawal

· April 30, 2018

We’ve all heard of substance addiction, tolerance, and withdrawal. But what exactly do those words mean?

As it’s commonly understood, the term substance abuse disorder applies to all substances that affect a person’s state of mind and behavior when introduced into the body. Among these substances are legal drugs such as alcohol and cigarettes as well as illegal substances like cannabis, cocaine, and LSD.

Today’s data on the prevalence of psychoactive substance abuse is shocking. 91% of people age 15 and older have consumed alcohol and 64% have consumed tobacco. It’s even more worrisome if we look at the figures on substance abuse between the ages of 14 and 18. 66% of this group affirm having consumed alcohol and 37% having used tobacco in the last month.

Some key aspects to understanding why substance addiction occurs are the processes of tolerance and abstinence. These two processes are closely linked because they are both compensatory responses of the body. But before we explain, we need to understand what happens in our brains when we use drugs.

A sad girl is crying because of substance addiction.

Substance abuse and the reward system

Most psychoactive substances are closely related to dopamine and the reward system of the brain. Dopamine is a neurotransmitter released when we perform “pleasant” actions. Its function is to reinforce these behaviors so we’ll repeat them in the future. Dopamine is basically the “prize” our body gives us. It makes us feel pleasure when we do something it perceives as right.

Drugs trigger or even simulate the release of dopamine in our reward system. Some of them, such as alcohol, do it through indirect mechanisms. Other drugs simply have a similar chemical composition and act like dopamine would. Amphetamines are an example of this last group.


This false release of dopamine when consuming drugs causes our reward system to activate. So we associate certain situations with a sense of pleasure. The brain thinks that the use of these substances is beneficial for the body, even when it’s actually the opposite and they are very harmful.

That said, these large discharges of “false dopamine” also cause a severe imbalance in the individual’s homeostasis. This imbalance leads the body to activate its regulatory mechanisms to fix it. This last step is what causes both tolerance and withdrawal, processes we’ll explain below.

Tolerance and withdrawal syndrome in substance addiction

The body’s regulatory mechanisms prevent an internal imbalance from occurring by modulating our brain chemistry. Drug abuse is an example of a situation where this happens. Let’s see what it’s all about.

Let’s imagine that every Saturday you go out and have a few drinks of any alcoholic beverage. Since alcohol is a drug that mimics endorphins, your endogenous opioid system will be hyperactivated. In turn, this will generate the release of dopamine and feeling of pleasure. If you repeat this behavior, your body will learn from it and generate a compensatory response.

This is where tolerance to drugs comes in. The following Saturday when you go out again, your brain will already know that you’re about to consume alcohol and that this will cause an imbalance. So it will lower the basal levels of endorphins.

This will cause your endogenous opioid system to become depressed, but it’ll return to normal after you start drinking. Your subjective feeling will be that alcohol doesn’t have any effect on you. Hence, you’ll have to drink more to make up for the compensatory drop due to tolerance.

Now, what happens if you suddenly stop drinking alcohol? What happens with that compensatory response? Even if you reduce your alcohol consumption to the minimum or eliminate it completely, the compensatory response continues.

Going back to the previous example, if you go out with no intention of drinking alcohol, your brain will still think that you’re going to do so. This is what previous experiences have taught it.

Therefore, your endorphins levels will drop precipitously. Since there’s no compensation with the consumption of alcohol, anxiety will result. This is what is known as withdrawal syndrome.

A man battling anxiety.

In conclusion

Tolerance and withdrawal are clear symptoms of substance addiction. If symptoms of tolerance start to appear, then withdrawal symptoms will also appear when there is no drug consumption.

On top of that, withdrawal symptoms usually leads to the person consuming the substance in order to feel better. We must take into consideration these biological mechanisms in order to understand the processes of substance addiction.

Substance abuse is a global health problem. We must understand that it causes a multitude of social, work, personal, and health problems. Additionally, if we want to improve people’s quality of life, it’s essential to raise awareness of how drugs work so that people understand the risks.