Block I Illinois Library Illinois Open Publishing Network

2 How Drugs Work in the Body and the Brain


Drugs are chemical substances that when taken into the body can have great impacts on the brain and the body systems.  Knowing how the brain works, and the impacts that drugs can have on brain function and behavior, will give you the knowledge and power to make decisions about your own drug use.

Learning Objectives

  • Know what glia, neurons and neurotransmitters do in the brain
  • Describe how psychoactive drugs affect the brain when they interact with neurons
  • Understand how drugs work in the brain and body
  • Understand drug impacts on various body systems
  • Describe and understand the Biomedical and Biopsychosocial models

Learning Content

What happens to your brain and body when you take drugs? Taking drugs impacts the brain. Taking drugs impacts homeostasis (steadiness between the different  elements) between the glia cells and neurons in the brain.

Glia cells maintain homeostasis and provide protection and support for neurons in the central nervous system and the peripheral nervous systems.

The main functions of glia are to hold neurons in place by surrounding them, supply oxygen and nutrients to neurons, insulate one neuron from another, remove dead neurons and destroy pathogens, and help with synaptic connections and physiological processes (Brodal, 2010).

Neurons are cells that communicate with other cells via synapse connections.  There are three types of neurons:

  1. Sensory neurons respond to stimuli by sensing signals sent to the brain and spinal cord
  2. Motor neurons receive signals from the brain and spinal cord
  3. Interneurons connect neurons that are in the same region in the brain and spinal cord

Image 2.1 – Neuron Cell Diagram

Brain nerve cell diagram
“Complete neuron cell diagram numbered” by LadyofHats, Wikimedia Commons, Public Domain

Synapses permit nerve cells to pass electrical or chemical signals to another neuron.

Image 2.2 – Chemical Synapse Schema

Synapse in the brain showing the neurotransmitter, receptor, and synapse gap. A synapse is the small gap between two neurons, where nerve impulses are relayed by a neurotransmitter from the sending neuron to the receiving neuron.
“Chemical synapse schema cropped” by US National Institutes of Health, National Institute on Aging, Wikimedia Commons, Public Domain

Neurotransmitters are chemical messengers that transmit messages across a synapse.

Image 2.3 – Neuron Synapse During Neurotransmitter Re-Uptake

Synapse during neurotransmission of chemicals in the brain.
“Reuptake both” by Sabar, Wikimedia Commons, Public Domain

Psychoactive drugs alter brain functions and act on the brain by altering the neurotransmitter availability at the synapse or by interacting with the neurotransmitter receptor itself. These types of drugs alter chemical levels in the brain which impact mood and behavior, which is what the neurotransmitters try to help manage.

Check Your Knowledge

Drug Effects on the Brain and Body

Watch this short video on how drugs affect the brain:

Video 2.1 – How Do Drugs affect the Brain


Many drugs are made of chemicals that are similar to chemicals that already exist in the brain.  Drugs alter the way messages from nerve cells are sent, received and processed in the brain.  Drugs alter the messaging in the brain in these four ways; the natural chemical messengers are imitated by the drug, the reward circuit of the brain is overstimulated by the drug, the drug floods the brain and it becomes overwhelmed by the chemical in the drug, or the drug binds to the brain receptors and alters the brain’s function.

Heroin and marijuana tend to fool the brain’s receptors and activate abnormal messages that are sent by nerve cells.  These messages cause a “high” that you feel when you take the drug.

Methamphetamine and cocaine cause nerve cells to release large amounts of neurotransmitters that cause signals from neurons to not shut off, causing an amplified effect in the brain. Again, a high occurs; it is just a different type of high.

All drugs indirectly or directly affect the reward system in the brain. The overstimulation in the system produces a euphoric effect that occurs in response to the drug. The euphoric effect can mimic something that the brain thinks is normal and needed, like eating or feeling the love of someone that cares for you.  The brain’s response can compel some people to seek that drug again and more often because the reward system desires the effect (NIDA Drugs, brains, and behavior: The science of addiction preface, 2021).

Image 2.4 – Brain’s Pleasure Center

The brain reward system; showing how eating food and taking cocaine can increase dopamine in the brain.
“Some drugs target brain’s pleasure center” by US National Institute of Health, Drugs, Brains, and Behavior: The Science of Addiction (2020), Public Domain

This video on addiction can help you better understand how overuse of a drug can lead to the need to continue using the drug.

Video 2.2 – The Chemistry of Addiction

Check Your Knowledge

Drug Impacts on the Brain

All psychoactive drugs increase dopamine in the brain.  When you take drugs, the brain responds to the overwhelming “noise” from the drugs by adjusting the reward circuit  so that the pleasure from the drugs is reduced.  The surges in dopamine and other neurotransmitters produce less dopamine, causing fewer receptors to exist that can receive the signals.  Most drug users see a decline in dopamine production that becomes very low, causing the reward from use to be decreased and less pleasure as a result of taking the same amount or more of the drug.  Most users eventually feel depressed, lifeless or numb; eventually they do not enjoy things that once brought them pleasure.  To compensate for the lack of pleasure, typically the user will take more and more trying to bring the dopamine levels in the brain back to normal so the reward circuit provides the pleasure they desire.  Unfortunately, the user becomes tolerant to the drug and to create a dopamine high, larger amounts of the drug must be taken.

When a user continues to take drugs, the misuse of the drugs leads to changes in the function and structure of the brain.  Most people start taking drugs voluntarily, but as use continues and addiction occurs, drug users’ self awareness and ability to make good decisions is impacted by the messages the brain receives causing intense impulses to take more drugs (NIDA Drugs, brains, and behavior: The science of addiction preface, 2020).

Drug Impacts on Various Body Systems

Drugs primarily impact the central nervous system but other body systems are impacted as well. No matter what the drug or how much of the drug there is, it cannot have an effect on the brain or in the body unless it is taken.  Living organisms must take a drug for an effect to appear. Life sustaining functions in the central nervous system related to thinking, breathing, sleeping and heart rate can all be impacted when drugs are taken into the body. Other body systems are also impacted by drug use. The body may experience a change in hormonal function within the endocrine system.  The cardiovascular system is at higher risk of attacks and increased heart rate and blood pressure when drugs are taken.  The respiratory system slows down or can increase when certain drugs are taken.  The GI system is often irritated by drug use causing diarrhea and stomach upset.

Critical Thinking

What are the direct and indirect impacts of using drugs on the brain and body?

Describe how drugs impact the brain.  What concerns you most about the use of drugs and the possible long term implications of use on your brain?

Why is it so easy to become addicted to a drug?

Biomedical Model

Ill health is caused by biological factors that are linked to lifestyle choices and the best course of treatment and recovery of the patient is the main concern.

Video 2.3 – Biomedical Versus Biopyschosocial Models of Healthcare

Biopsychosocial Model

Image 2.5 – Biosychosocial Model of Health

Infographic of the biopsychosocial model of health showing how social, biological and psychological factors can impact individual and drug use.
“Biopsychosocial Model of Health 1” by MrAnnoying, Wikimedia Commons, CC BY-SA 4.0

To understand a person’s medical condition you need to understand the connections between biology, psychology, and the environment in which the person lives. All three of these factors impact the human body in different ways.

Video 2.4 – The Biopyschosocial Model

It is important to consider all aspects of health and mind when looking at the impact drugs can have on the brain and body.  Think about the risk of addiction for you, the people you care about and your community.  What will you do to minimize these risks for yourself and others?

Supplemental Resources

National Alliance of Mental Health. (n.d.). Home [Homepage].

National Conference of State Legislatures. (2018, February 23). Pharmaceuticals.

National Institute of Drug Abuse. (2017, March 9). Impacts of drugs on neurotransmission [Archived webpage]. U.S. Department of Health and Human Services, National Institutes of Health, Retrieved September 6, 2021 from

National Institute on Drug Abuse. (2018, June 6). Understanding drug use and addiction drug facts. U.S. Department of Health and Human Services, National Institutes of Health. Retrieved July 6, 2021, from

National Institute of Drug Abuse. (2020, July). Drugs, brains, and behavior: The science of addiction preface. U.S. Department of Health and Human Services, National Institutes of Health. Retrieved July 16, 2021, from

National Institute of Drug Abuse. (2021, March 11). Opioid overdose crisis. U.S. Department of Health and Human Services, National Institutes of Health.

The University of Queensland. (n. d.). Websites and apps – Neuroscience [LibGuide].

Watkins, M. (2021). How drugs affect the brain and central nervous system. American Addiction Centers. Retrieved July 6, 2021, from


Brodal, P. (2010). The central nervous system: Structure and function (4th ed.). Oxford University Press.

Green, H. [SciShow]. (2012, November 18). The chemistry of addiction [Video]. YouTube.

National Institute of Drug Abuse. (2020, July 20). Drugs, brains, and behavior: The science of addiction preface. Retrieved July 16, 2021, from

National Institute of Drug Abuse. (2020, July 10). Some drugs target brain’s pleasure center [Chart]. U.S. Department of Health and Human Services, National Institutes of Health. Retrieved July 26, 2021, from

Percuoco, K. [drkevin_percuoco]. (2020, March 6). Biomedical vs biopsychosocial models of healthcare [Video]. YouTube.

Sabar. (2020, September 21).  Reuptake both.png [Diagram]. Wikimedia Commons. Retrieved September 5, 2021, from

Samra, J. MyWorkplaceHealth. (2020, January 21). What is the bio-psycho-social model? [Video]YouTube.

TED-Ed. (2017, June 29). How do drugs affect the brain? -Sara Garofalo [Video]YouTube

MrAnnoying. (2020, March 22). Biopsychosocial model of health 1.png [Diagram]. Wikimedia Commons. Retrieved September 5, 2021, from

U.S. National Institutes of Health, National Institute on Aging. 2020, December 8). Chemical synapse schema cropped.jpg [Image]. Wikimedia Commons. Retrieved September 5, 2021, from


Icon for the Creative Commons Attribution-NonCommercial 4.0 International License

Drug Use and Misuse Copyright © by University of Illinois Board of Trustees is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.

Share This Book