THE CHEMISTRY OF ADDICTION

Madelyn Winward

CHEM 1010

November 21, 2021

The Chemistry of Addiction

The human brain is the most complex organ in the body that is often likened to that of a

computer. The brain serves to regulate the body’s most basic functions, interprets and responds to

everyday experiences, and shapes behavior. The brain consists of billions of cells called neurons

that are organized into circuits and networks in order to send messages.

Drugs interfere with the way neurons send, receive, and process these messages via

neurotransmitters. Drugs similarly alter important areas in the brain that are important to sustain

healthy living and marks compulsive behavior such as addiction. One area in the brain that is

most impacted is the basal ganglia which is largely involved in positive motivation including

pleasurable activities such as eating, sexual relationships, and socializing. Drugs over-activate

this circuit, commonly referred to as the brain's “reward circuit.”

When drugs are taken, they cause surges of neurotransmitters much greater than the

naturally produced levels in association with healthy rewards. These neurotransmitters most

commonly associated with addiction are dopamine, serotonin, and endorphin. Not only do these

drugs alter the levels of these neurotransmitters but they also exploit the brain’s ability to

remember unnatural highs and serves to motivate one to seek out more of these experiences.
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Since the beginning of time, humans have had to act as hunters and gatherers in order to

survive. The brain rewards the body for things like gathering food, having intercourse, and

running from danger. This was the system that allowed us to survive and evolve for thousands of

years to the present day where we no longer have to look very hard in order to find pleasure.

The brain has since figured out how to do these things not to survive, but now for

entertainment’s sake. This has seemingly accidentally paved the way for addiction due to

neurotransmitters in the brain. Excitatory neurotransmitters increase the likelihood that the

neuron will fire an action potential. Inhibitory neurotransmitters have the opposite effect by

decreasing the likelihood of firing an action, serotonin being a common example. Endorphin and

dopamine are the dangerous excitatory neurotransmitters that addiction takes advantage of.

Dopamine is responsible for the reward mechanisms in the brain and is at the highest during

intercourse or during activities important to one’s survival.

The hypofunction reward system is responsible for the brain developing tolerance to

these significant increases in excitatory neurotransmitters. As an addict continues to use, drugs

that cause addiction imitate natural neurotransmitters or artificially change the levels of them.
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Heroin and morphine are the biggest examples and are highly addictive due to their similar

structure to endorphin which was discovered by researchers from John Hopkins University in

1972.

Endorphins are considered to be natural opiates of the body that fuel the feeling of

euphoria and reduce pain by interacting with receptors in the brain. Morphine acts similarly by

locking onto endorphin receptor sites on nerve endings and magnifies the effect of endorphins.

Once the artificial high has passed, the brain craves to return to that experience, thus manifesting

addiction.

Another example is nicotine which mimics acetylcholine that triggers a large increase in

dopamine. Glutamate is also released in response to leverage the impact. These two chemicals

create what scientists call a, “memory loop,” which reinforces the habit.
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Scientists work closely with medical professionals and have seen first hand what

addiction looks like. “Under the direct influence of the disease, the addict is in an altered state of

consciousness.” (Kathy Bettinardi-Angres, 2010) Which is to say that the chemicals that one

intakes directly affects the brain’s circuitry and not only temporarily alters one’s consciousness

but has a lasting impact on that person’s ability for comprehension and decision making.

There are four main brain circuits involved with addiction and drug abuse.

1. Reward: located in the nucleus accumbens.

2. Motivation/drive: located in the orbitofrontal cortex. (OFC)

3. Memory and learning: located in the amygdala and the hippocampus.

4. Control: located in the prefrontal cortex.

It is important to note that other parts of the brain operate within each circuit and play large roles

in addiction such as cerebellum and thalamus responsible for emotion and attention.

The model above suggests that for an addicted individual, their saliency value is

modified. “It is postulated that the high reward value of drugs leads to a resetting of reward

thresholds, which then results in decreased sensitivity to the reinforcing properties of naturally

occurring stimuli.” (J Clin Invest, 2003) Without the ability for control, a positive-feedback loop

is set forth that results in the habitual drug intake.

The chemistry of addiction is a developing topic as more information becomes available.

Overstimulation seems to be inevitable in a world centered around immediate gratification and

pleasure. On a purely chemical level, addiction can seem easy to understand. However, with the

world constantly changing, there are countless ways the causes of addiction can develop.
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References

Butanis, B. (2018, August 9). The Science of Addiction. Johns Hopkins Medicine, based in

Baltimore, Maryland. Retrieved November 21, 2021, from

https://www.hopkinsmedicine.org/opioids/science-of-addiction.html.

Kathy Bettinardi-Angres, MS, RN, APN, CADC, and Daniel H. Angres, MD. (2010, July).

Understanding the disease of addiction - NCSBN. Journal of Nursing Regulation.

Retrieved November 21, 2021, from

https://www.ncsbn.org/Understanding_the_Disease_of_Addiction.pdf.

Public Broadcasting Service. (n.d.). Heroin in the brain | the opium kings | frontline. PBS.

Retrieved November 21, 2021, from

https://www.pbs.org/wgbh/pages/frontline/shows/heroin/brain/.

SciShow. (2012, November 28). The chemistry of addiction - youtube. SciShow. Retrieved

November 21, 2021, from https://www.youtube.com/watch?v=ukFjH9odsXw.

Staff, L. S. (2011, August 15). Addiction now defined as brain disorder, not behavior problem.

LiveScience. Retrieved November 21, 2021, from

https://www.livescience.com/15563-addiction-defined-brain-disease.html.

Volkow, N. D., Fowler, J. S., & Wang, G.-J. (2003, May). The addicted human brain: Insights

from imaging studies. The Journal of clinical investigation. Retrieved November 21,

2021, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC155054/.