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How does addiction work in the human body?

Cracking the code that addiction runs on.

Every day, 22 years old Harsh wakes up early in the morning. It had become a routine, one that he had no control or choice over. He is usually out of breath, under stress and always on the edge. But it’s not a chronic ailment or an infectious disease that is bothering him – he just hasn’t had his fix in a while.

What is his fix? It could be anything from substance-abuse (alcohol, marijuana etc.) or otherwise (gambling, shopping, the Internet, gaming etc). And every day, countless people like Harsh wake up to another day where their lives are affected by their addictions – mostly in a very bad way. To understand their plight, one must understand addiction itself, and what it does to the human body. But first…

…Take it seriously

Addiction and its effects are not to be taken lightly. There is a certain tendency to label one’s affinity towards certain things as addiction. For instance, how many times have you heard, “I’m addicted to this song!” or “I can’t do without my morning coffee, I’m addicted to it”. While there is nothing wrong with either statement spoken casually, it also belittles a situation where a person might actually be addicted and refuse to acknowledge it as a problem. So first things first, beyond obvious signs, if you or anyone you know might repeatedly refer to something as addiction, sit up and take notice.

The biology

While quite a lot of physical effects that are present in drug-induced addiction are missing from behavioural addiction, they are both, at a neural level, the same. And to understand one would be to understand another up to some extent. So, what causes us to be addicted? We start off with understanding neurotransmitters.

A simplistic diagram of how two neurons interact

Our body functions the way it does largely due to our brain controlling it via the nervous system. In this system, every part of our body is linked to our brain with nerves either via our spinal cord or directly. These nerves, in turn, are made up of nerve cells. But these nerve cells, or neurons, are not connected continuously – they have gaps in between them called synapses. And when a signal to or from the brain needs to cross this synapse, it is carried over by chemicals known as neurotransmitters.

Drugs can play havoc with neurotransmitters – flood the brain with excess neurotransmitters, stop the brain from making them, bind to receptors, causing the neurotransmitters to be destroyed and way more. And that is what causes addiction.

The role of dopamine

All major drugs of abuse create excess dopamine in the body that causes a feeling of pleasure. In excess, drug abuse leads to high level of dopamine in the body. But wait, if it makes you feel happy all the time, what’s wrong with that? Enter homeostasis.
Without going into too much detail, homeostasis can be explained as the tendency of the human body to maintain its state. That includes the brains and the neurotransmitters it produces as well. Once acclimated to, say, a high supply of dopamine from a drug, the brain reduces its own production capacity to maintain a normal level. But this causes low dopamine level when the drug is not being used, eventually leading the user to depression, stress and the belief that the only relief they can get is through the drug.

And this is not just limited to drug addiction. A 2009 study by the Scripps Research Institute concluded that the same molecular reactions that occur with human drug addiction also show up in compulsive overeating in obese rats. The receptor that was studied – D2 – is responsible for vulnerability to drug addiction in humans and responds to dopamine, a central neurotransmitter released in anticipation of rewarding, satiating experiences such as those involving food, sex or psychoactive drugs. When checked, it was found to be up-regulated in obese rats exposed to a high-fat diet, and the sensitivity to dopamine went even lower when the rats were allowed to continue their compulsive eating behaviour.

Smartphone addiction has even created a new form of muscular ailment known as text neck

In a now classic experiment that has been repeated a number of times, researchers attached electrodes to rodents in such a way that when activated, they stimulated the reward centres of the brain. This activation can be done by a button in the enclosure, which is repeatedly done by some rodents until they reach the point of passing out due to exhaustion. This is important since biochemical processes work in a remarkably similar way in rodents and humans too. Even in humans, the effect of behavioural compulsion is the same.

Other factors

One of the most common conceptions associated with alcohol and other forms of drug abuse is the eventual degradation and death of brain cells. Research indicates that alcohol abuse eventually reduces the size of the brain, methamphetamine kills cells that produce dopamine and trigger apoptosis, a process where cells self-destruct. Needless to say, a brain with fewer cells to do its tasks is less capable of things like judgement, willpower and making the secession to addiction involuntary.

Another factor that influences addiction is genetics. The FosB gene has a splice variant ΔFosB that is agreed to be a critical factor in almost all forms of behavioural and drug addictions. To put it simply, ΔFosB can be described as a “sustained molecular switch” when it comes to developing an addiction. And like all genes, it can be inherited – and there’s been sufficient research to establish that it has been. For instance, children of alcoholic parents, even when adopted by non-alcoholic parents, have shown a greater tendency towards developing an addiction.


With or without genetics, there are other ways to detect a risk of addiction as well. While the judgement on genes being used to diagnose addiction is still in debate, Henri Begleiter, PhD, Professor of Psychiatry and Neuroscience at the State University of New York in Brooklyn, New York, has come up with a new method to detect the risk of an addiction through brain waves.

Brainwave analysis can detect addiction tendencies

Brain waves are usually measured through an electroencephalograph and printed out as an electroencephalogram (EEG). Anyone experiencing any significant light or sound stimuli shows a peak in the graph of values of about 300-500. For addicts the peak is lower, which means that they cannot distinguish between everyday stimuli and special stimuli, thus processing each one as new, a characteristic called hyperexcitability. This excited state is often dulled down by going after more drugs. This distinct difference in the EEG graphs of addicts and non-addicts can help in early detection of addiction tendencies.

The Cure

The knowledge of the impact neurotransmitters and specific chemicals can have on the functioning of the brain can help create medicine for specific addictions – and it has. For instance, methadone for heroin addicts, naltrexone for alcoholics, and bupropion for nicotine addicts do exactly that.

Once detected, people can even join treatment programmes and support groups to deal with their addiction in a better way

In addition to that, knowing that there are other factors apart from one’s own choice can help individuals and families come to terms with addiction more easily. Taking it one step further, knowing about an inherited tendency towards addiction, people can choose to abstain from substances and addictive behaviour altogether. This does impact the brain – as people keep away from the people, places and activities that caused their addiction, the brain gradually dissociates the availability of those factors and the eventually induced pleasure from addiction.


Even though we have discussed the physiological and neurological details about how addiction works in the previous sections, one of the most important factors behind addiction has been missed out – us. Both drug and behavioural addictions are dependent on us taking the first step or deciding where to draw the line. Irrespective of which gene we’ve inherited or how our addiction has already affected us, if a choice is made to say a simple ‘No’ and then stick to it, then it is certainly possible for a mind to win the battle against addiction.

Arnab Mukherjee

Arnab Mukherjee