The Physiology of Substance Use

Substances impact people's emotions, behaviors, and cognitions by interacting with or mimicking neurotransmitters. It is important that counselors have an introductory understanding of physiology, as neurological research has a strong potential to alter conceptual paradigms that drive the ways in which counselors understand and intervene with clients.

Recommended Readings & Resources

To get the most out of this unit, please review the following:

  1. Neuron Terminology Notes
  2. Hyman, 2005
  3. NIDA Impacts of Drugs on Neurotransmission Article
  4. Mouse Party
  5. Tang, Posner, Rothbart, & Volkow, 2015

Learning Objectives

After completing this unit, students will be able to:

  1. Draw a neuron and label the soma, dendrites, axons, terminal buttons, and synapse.
  2. Describe the function of each of the parts listed in the previous question.
  3. Conceptualize drugs' effects as stemming from changes in neurotransmitter levels.
  4. Describe current limitations associated with using brain imaging techniques for diagnostic purposes.

Introduction to Neurons

Substances including marijuana, cocaine, and many prescription medications work by altering the way that neurons and neurotransmitters function. In the following videos, you will learn the different parts of a neuron, what an action potential is, and how neurons send messages from one neuron to the next. This information is foundational to understanding how substances can alter neurophysiology.

Notes on Neurons and Neurotransmitters

Click here to download a notes page that includes vocabulary definitions as well as an overview of the process of signaling within and between neurons.

Intro to Neurons

Playback problems: This video is available on YouTube at

The transcript for the Introduction to Neurons video is available for download here.

Action Potentials Within Neurons

Playback problems: This video is available on YouTube at

Signaling Between Neurons

Playback problems: This video is available on YouTube at


For an introduction to neurons and neurotransmitters, read the following article:

  • Hyman, S. E. (2005). Neurotransmitters. Current Biology, 15(5), R154-R158.

Overview of Neurotransmitters

Check out this webpage for an overview of some of the neurotransmitters.

Substances' Effects on Neurotransmitters

Psychoactive substances produce their effects by changing people's neurotransmitter levels. Check out this page on MITs website for a summary of how different substances interact with neurons and neurotransmitters.

The National Institute on Drug Abuse (NIDA) also summarizes how neurotransmitters are impacted by drugs. Check out their webpage.

If you are interested in gaining a more in depth understanding of how opioids impact neurotransmitters, read through Froehlich (1997).

Check out the Mouse Party site from the University of Utah to see how different substances impact mice.

Self-Control & Addiction

The following article exemplifies the ways in which neuroscience and physiology can impact the way that counselors conceptualize and intervene with clients. As you read through the article, try to lookup terms, such as prefrontal cortex and/or striatum that are not familiar. Many counselors and counselors in training will likely find this article to be information dense and difficult to understand. I encourage you to take your time, and to read through the article multiple times.

Introduction to Brain Imaging

Functional Magnetic Resonance Imaging (fMRI) is one type of brain imaging that tracks blood oxygen to make an image showing blood flow in different parts of the brain. The more active a part of the brain is, the more energy it uses, which means more oxygenated blood flows to active areas of the brain. Tracking blood flow in the brain allows researchers to better understand how things like substance use impact brain functioning. Gaps or holes (areas without color) on a fMRI image do not mean that area of the brain is dead, or that a real hole exists in the brain. "Holes" on an fMRI image simply mean that area if the brain is less active. I have not seen any research or credible evidence that using drugs puts holes in a person's brain.

Positron emission tomography (PET) scans are another brain imaging technique that uses radioactive chemicals (isotopes) to map brain activity. PET scans are useful for researchers who seek to understand specific neurotransmitters in the brain. Recall from the video on action potentials that ligands bind with receptor sites on neurons to generate an action potential. Scientists attach radioactive isotopes that are detected by PET scans to specific ligands, so that they can visualize receptor sites. Thus, PET scans provide valuable information, such as which brain regions contain receptors for particular substances.

Brain imaging techniques are sometimes misrepresented in the media. For example, reports that drugs put holes in a person's brain:

A healthy brain is smooth and full, but the addicted brain is so severely atrophied that it resembles Swiss cheese. Neuroscientist and psychiatrist Dr. Daniel Amen says these brains are less active, less healthy, and shriveled in appearance and have an overall toxic look, as if acid had been poured over them. Dr. Amen has found that "cocaine and methamphetamine abuse appear as multiple small holes across the cortical surface...
(Jay & Jay, 2008, p. 24)

Statements such as the above quote are inaccurate and misrepresent brain imaging techniques as well as the ways in which substance use impacts brain functioning. Brain imaging studies demonstrate that taking substances can alter brain functioning, activity, and density, however, drugs do not put holes in someones brain. Drugs do not make a brain resemble Swiss cheese. Drugs do not make a brain appear as though acid were poured on it.

Dr. Daniel Amen is a celebrity psychiatrist who has faced criticism from within the scientific community. You can read about him in this Wired Magazine article.

Brain Imaging as a Diagnostic Tool

Brain imaging techniques, including fMRI, PET, SPECT, CAT, and others, are important diagnostic tools. Physical health conditions, such as tumors or traumatic brain injuries (TBIs), sometimes present as mental health disorders. Physicians may use brain imaging to rule out diagnoses such as cancer or TBIs. There are currently not enough data to use brain scans as a diagnostic tool for mental health conditions that are not caused by physical health ailments (e.g., depression, anxiety, PTSD, substance use disorders, etc.). However, in the future, brain scans may become foundational mental health diagnostic tools. To learn more about using brain scans to diagnose mental health concerns, check out this blog from Harvard University.

The following video summarizes how fMRI works:

Playback problems: This video is available on YouTube at

Neurons & Neurotransmitter Exploration Questions

  • What was your experience engaging with the resources on this page?
  • How comfortable would you feel talking with a psychiatrist who is describing the effects of a medication that one of your counseling clients is taking?
  • Thinking back to the research unit, how congruent are the evidence based practice resources you found with what you learned in this unit?
  • Do you think counseling can change a client's physiology?
  • Briefly summarize:
  • The parts that make up a neuron including the soma, dendrites, axon, myelin sheath, nodes of Ranvier, terminal buttons, synapse, and synaptic vesicles.
  • How receptors on neurons bind with substances to allow protons to flow into the neuron.
  • What happens when a neuron reaches the threshold of excitation.
  • How neurotransmitters are used to send signals between neurotransmitters.
  • How do drugs impact neurotransmitter levels in the brain?
  • Describe which neurotransmitters are altered when a person uses different drugs.
  • List two brain imaging techniques.
  • How does each technique work?
  • What additional research or information do you think is needed before mental health professionals can use brain imaging techniques to diagnose mental health conditions?