Colin MacKenzie M.D.
January 5, 2020

What is a Substance Use Disorder?

According to the Diagnostic and Statistical Manual or Mental Disorders-5 (DSM-5), a Substance Use Disorder is a “cluster of cognitive, behavioral, and physiological symptoms indicating that the individual continues using the substance despite significant substance-related problems”.  The hallmark of an addictive substance is one that directly activates the brain reward system producing a “high” or euphoria that then leads to the creation of strong memories and the reinforcement of maladaptive behaviors focused on the continued use of the substance.   All substances of abuse work by “hijacking” the brain’s reward system, though each substance may do it via different chemical and physiological mechanisms.  It is also now recognized that those who become addicted to a substance have genetic (and possibly non-genetic) risk factors that predispose them to addiction before ever having exposure to the problematic drug.   

What is the difference between Substance Misuse, Abuse, Dependence, and Addiction? 

Thought the DSM-5 does not make a distinction diagnostically between Misuse, Abuse, Dependence, and Addiction; many clinicians find it useful to draw a distinction between these entities for educational and treatment purposes.

Misuse of a substance is generally defined as the use of any substance outside of the originally intended purpose.  Just about everyone has misused a substance at one time or another such as taking a dose of aspirin prescribed for a headache to treat a toothache. 

Abuse is often defined as a pattern of misuse of a substance that also causes recurrent difficulties in various life functions such as the legal problems, problems in relationships, or inability to fulfill major role obligations at school, home, or work.  Many clinicians believe that abuse is just the early stages of addiction, but many individuals who abuse a substance do not also have physiological dependence or “irresistible” cravings often seen in addiction. 

There is significant debate and confusion around the use of the terms “dependence” and “addiction”.  For purposes of this discussion, we will be referring to physiological dependence, which usually refers to physiological responses, such as tolerance or withdrawal, that occur after prolonged, repeated exposure to certain substances.  For example, if someone consumes alcohol on a daily basis, tolerance is commonly seen where the person needs to consume ever-larger amounts to achieve the same effect.  Likewise, if that same person were to stop the use of alcohol suddenly, withdrawal symptoms can occur such as tremor, anxiety, sweats, and increases in heart rate.  Most people will have some degree of physiological dependence if exposed to a substance for a long enough period of time.  The severity of the physiological symptoms depends on multiple factors including age, genetics, general health status, type of substance used, duration of use, and quantities used.  It is important to understand that evidence of physiological dependence DOES NOT mean a person suffers from addiction.  Even if a person requires time in a detox facility to wean themselves off of a substance does not necessarily equate with them being "addicted" to that substance.  

Addiction, on the other hand, typically refers to a specific psychological reaction with a consequent pattern of behavior upon exposure to a substance.  In those who are predisposed (either genetically or otherwise), the addicted individual experiences a “high” or “euphoria” that leads to intense cravings with associated maladaptive behaviors focused on the continued seeking and use of the substance often with very detrimental consequences.  Physiological dependence is almost always present in addicted individuals and the associated tolerance can lead to a cycle of increasingly large quantities of use, sometimes with lethal amounts of a substance, and severe withdrawal symptoms requiring medical attention.  The addicted individual will often describe a “loss or decrease of control” with the inability to cease their drug use despite experiencing severe negative consequences.  Addicted individuals will often describe an emotional “disconnect” where cravings minimize expected reactions of guilt and shame leading to continued use in the face of harming themselves and the ones closest to them.