Explainers Harm Reduction

Drug Use 101: Substance Use Disorders

by Chelsea Boyd

Oct 24, 2024

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Author

Chelsea Boyd

Resident Research Fellow, Harm Reduction

Key Points

“Addiction” is often used interchangeably with SUD, although it is less precise and the terms are not synonymous.

Long-term substance use can lead to changes in brain function, which can make it harder to stop using the substance.

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Background

People use substances in different ways. For example, one person might only consume alcohol on special occasions, another might have a drink with dinner every night, and yet another might drink large quantities on the weekends but not during the week. All three of these people have a different relationship with alcohol—but do any of them have substance use disorder (SUD)? This depends on how their alcohol use interacts with their bodies and lives. Now imagine that the same three people use opioids instead of alcohol. Does substituting a less commonly used substance change the perception of whether these people have SUD?

These overly simplistic examples show that most people do not use a consistent definition when they think about problematic substance use. Not only does this show up in perception, it occurs in language, too. People, some providers, and the media often use terms interchangeably when talking about problematic substance use. This is most common with “addiction” and “substance use disorder,” although “dependence” is also used occasionally. Fortunately, health providers and organizations have more precise criteria for diagnosing problematic substance use.

When Does Substance Use Become SUD?

Not everyone who uses substances has SUD. Although health authorities define SUD slightly differently, most definitions hinge on a requirement that the substance use continues despite interfering with the person’s life or health. The most commonly used diagnostic tool for SUD, the American Psychological Association’s fifth edition of The Diagnostic and Statistical Manual of Mental Disorders (DSM-V), lists 11 symptoms for nine different classes of substances (e.g., opioids, alcohol, cannabis, tobacco). It further specifies that SUD can have different levels of severity. If a person has two to three of the 11 symptoms, then their SUD is mild; four to five symptoms is moderate; and six or more symptoms is severe. While these diagnostic criteria make diagnosing SUD seem straightforward, they actually allow for more than 1,100 combinations of symptoms for each substance. For this reason, people who use substances should consult with a health care provider if they think they may have SUD.

Substance use and SUD manifest differently for each person. While physical dependence can be a symptom of SUD, not all people with SUD are physically dependent on a substance. For example, a person can have SUD without experiencing cravings or withdrawals. And depending on their symptoms and life circumstances, some people who meet the criteria for SUD may have few problems carrying out their day-to-day functions and responsibilities.

Similarly, a person can have a diagnosable SUD without having a compulsion to consume the substance, as the definition of “addiction” specifies. This means that SUD and addiction are not necessarily the same and that addiction does not apply to every person with SUD (although it can). Unlike SUD, addiction does not have specific diagnostic criteria and can apply to behaviors unrelated to substance use, such as gambling. Overall, addiction is a more ambiguous term than SUD, and there is still discussion around how to measure addiction objectively.

What Causes SUD?

The exact cause of SUD has not been established. Just as SUD is a complex disorder that can manifest differently from person to person, its causes are complex and varied. This makes it difficult to determine which factors directly cause SUD and which merely correlate with developing SUD. A further complication in pinpointing a specific cause is that different experiences and characteristics interact, creating risk factors for one person and protective factors for another.

From a biological perspective, the way a substance affects the body can contribute to the risk of developing SUD. Long-term substance use can lead to changes in brain function, which can make it harder to stop using the substance. In addition to neurological changes, genetics can increase a person’s likelihood of developing SUD.

Biology is not the only factor that can influence the development of SUD. Psychological and social conditions can also contribute. For example, SUD and mental health conditions often co-occur, although one may not directly cause the other. Stress created by environmental and social conditions can also lead a person to develop SUD. A few circumstances that can affect whether a person develops SUD include access to substances, social support and dynamics, cultural norms, and financial stability.

Conclusion

Words matter when talking about problematic substance use. Understanding that substance use is nuanced and affects individuals differently is vital to describing problematic use, reducing stigma, and addressing associated risks.