A host of biological processes relate to substance use, substance misuse, and substance use disorders (SUDs). Biological influences include genetics, neurobiology, and human development (which is a bio-psycho-social-spiritual process). Genetic evidence concerning substance use, misuse, and SUD will be examined. We will explore what might be going on in the brain with exposure to alcohol and other drugs (AOD)—basics about neurobiology. In this chapter, we look at basic information concerning neuroanatomy (parts/areas of the brain) and neurochemistry (neurons and neurotransmitters). Understanding these basic biological processes helps explain the brain-behavior relationship—how what goes on in the human brain relates to the human experience and human behavior. This content reflects a vast difference from the early (1930s) (mis)conception of addiction as resulting from a moral failing or weak willpower (NIDA, 2018). Quoting the director of the National Institute on Drug Abuse (NIDA, 2014), Dr. Nora Volkow:

“Drug addiction is a brain disease that can be treated.”

While bio-psycho-social-spiritual processes include additional factors, it is critically important to understand what is happening at the biological level if we are to understand and effectively intervene around substance use, misuse, and SUD. Substance misuse causes significant and persistent changes in the brain that relate to the experience of addiction (SUD), changes that may persist for long periods of time after substance use stops. Recovery from SUD does not necessarily return the brain to its original pre-SUD state, rather it again changes as it establishes a new state of “normal” functioning—some substance-induced changes are not reversible.

Relevant to discussing the biological basis of substance misuse are elements of human development—exposure to substances at critical developmental periods has a different impact than exposure at other times. In order to understand the biology of substance use, it is helpful to understand certain principles of pharmacokinetics and psychopharmacology—how drugs are processed/metabolized in the body, the biology underlying tolerance and withdrawal, the biology underlying drug actions (agonist, antagonist, and synergism), and how this knowledge might inform pharmacotherapy—the use of medication to help treat substance use disorders.

Reading Objectives

After engaging with these reading materials and learning resources, you should be able to:

• Explain evidence concerning the genetic basis of substance misuse and substance use disorders;
• Describe the roles played by different brain regions (neuroanatomy) in substance misuse and substance use disorder;
• Describe the roles played by neurotransmitters (neurochemistry/neurophysiology) in substance use, misuse, and use disorders;
• Explain why age at substance use initiation matters in determining substance use disorder outcomes;
• Identify the role of homeostasis processes in acquired tolerance and withdrawal;
• Describe basic principles of pharmacokinetics and psychopharmacology (drug half-life, synergism, agonists, and antagonists) and how this might relate to medication for assisting in treatment of substance use disorder (pharmacotherapy).