Substance use disorder is a treatable mental health condition that affects millions of people worldwide, disrupting their health, relationships, and daily life through problematic patterns of substance use that persist despite harmful consequences.
Understanding Substance Use Disorder
Substance use disorder, which was once commonly called drug addiction, is a mental health condition where a person develops a problematic pattern of using substances that significantly impacts their health and quality of life. This condition can involve many different substances, including alcohol, prescription medications, illegal drugs, and even tobacco. When someone has this disorder, they find it extremely difficult to control their use of these substances, even when they fully understand that continuing to use them is causing serious harm to themselves and the people around them.[2]
The condition exists on a spectrum of severity, ranging from mild to moderate to severe. What many people refer to as “addiction” typically represents the more severe end of this spectrum. Importantly, substance use disorder is recognized as a chronic disease, much like diabetes or heart disease, rather than a simple matter of poor choices or weak willpower. This understanding is crucial because it helps reduce stigma and opens the door to proper treatment and support.[6]
When substances enter the body, they cause changes in how the brain functions over time. These substances trigger the release of dopamine, which is a chemical in the brain that creates feelings of pleasure and reward. After the substance wears off, the brain and body begin to crave that good feeling again, creating a powerful cycle that can be very difficult to break without proper help and support.[2]
Common Types of Substance Use Disorders
Substance use disorder can develop with many different types of substances. Among the most common types are alcohol use disorder, opioid use disorder, cannabis use disorder, tobacco use disorder, methamphetamine use disorder, and cocaine use disorder. Each type involves the problematic use of a specific substance or class of substances that leads to significant problems in a person’s life.[2]
Alcohol use disorder stands out as the most frequently occurring type of substance use disorder in the United States. However, it’s not uncommon for someone to struggle with more than one substance at the same time. When a person has problems with multiple substances simultaneously, this is called polysubstance use disorder. For example, someone might have both alcohol use disorder and tobacco use disorder at the same time, which can make treatment more complex and challenging.[2]
The specific substances that can lead to substance use disorder include alcohol, cannabis (marijuana), hallucinogens, inhalants, opioids (both prescription pain medications and illegal drugs like heroin), sedatives and tranquilizers, stimulants and psychostimulants, and tobacco or nicotine products. Even some prescription medications and over-the-counter medicines, when misused regularly, can lead to the development of a substance use disorder.[6]
Epidemiology: How Many People Are Affected
Substance use disorder represents a major health issue affecting millions of Americans. According to national survey data, more than one in six Americans aged twelve or older experienced a substance use disorder in 2022. To put this into perspective, this means that in a single year, millions of people struggled with problematic substance use that significantly impacted their lives and wellbeing.[6]
Despite the high number of people affected, a troubling gap exists between those who need help and those who actually receive it. A 2023 national survey revealed that among Americans older than age twelve who reported experiencing a substance use disorder in the past year, more than eighty-five percent did not receive any substance use treatment during that time. This represents a significant public health challenge, as many people who could benefit from treatment are not accessing the help they need.[5]
Substance use disorders can affect people regardless of their race, sex, income level, or social class. No one is immune to developing this condition, and it touches families and communities across all demographics. The widespread nature of substance use disorders means that nearly everyone knows someone who has been affected, whether directly or indirectly, by problematic substance use.[6]
Causes of Substance Use Disorder
The exact cause of substance use disorder is not fully understood by medical science, but researchers have identified that changes in the brain’s reward system play a central role. When someone uses substances repeatedly, their brain begins to change in ways that make it increasingly difficult to feel pleasure from normal, everyday activities. The brain becomes dependent on the substance to trigger the release of dopamine and other chemicals that create feelings of reward and satisfaction.[2]
What starts as occasional or experimental use of a substance can gradually progress into a disorder over time. For some people, the transition happens quickly, while for others it may take months or years. With certain substances, particularly highly addictive drugs like crack cocaine or heroin, a person might lose control after using the substance only once or twice. Other substances may require more frequent or prolonged use before a disorder develops.[13]
The development of substance use disorder is rarely caused by a single factor. Instead, it typically results from a complex interaction of multiple influences working together. These include biological factors such as genetics, environmental factors including family and social influences, the person’s age or stage of development when they first start using substances, and the presence of other mental health conditions. Understanding these multiple causes helps explain why some people develop substance use disorders while others who use substances do not.[4]
Risk Factors
Several factors can increase a person’s risk of developing a substance use disorder. Understanding these risk factors is important because it can help identify people who may need extra support or prevention efforts. However, having risk factors doesn’t guarantee that someone will develop a substance use disorder, and people without obvious risk factors can still be affected.
Biological factors play a significant role in determining risk. Genetics and individual biology account for approximately half of a person’s risk for developing addiction. A person’s sex and ethnicity may also influence their vulnerability to substance use disorders. Additionally, the presence of mental health disorders such as depression, anxiety, or trauma-related conditions can significantly increase the risk, as some people may turn to substances as a way to cope with difficult emotions or psychological pain.[4]
Environmental factors are equally important in shaping risk. The people around us, including family members and friends, can influence substance use patterns. Socioeconomic factors such as poverty, lack of educational opportunities, or limited access to healthcare can also increase vulnerability. The age at which someone first begins experimenting with substances matters greatly—those who start using substances at a younger age face higher risks of developing substance use disorders later in life. Social and peer pressure, especially during adolescence and young adulthood, can push vulnerable individuals toward substance use.[4]
Symptoms and Warning Signs
Recognizing the symptoms of substance use disorder is crucial for getting help early. The symptoms vary depending on which substance is being used, but there are common patterns that appear across different types of substance use disorders. These symptoms can be grouped into two main categories: those that occur while the substance is in the body, and those that appear when the substance is wearing off or leaving the body.
When a substance is in the body, a person experiences what is called intoxication. During intoxication, the person may appear sleepy, unusually calm, overly excited, or display intense emotions that seem out of proportion to the situation. The substance affects their judgment and decision-making abilities, making it difficult for them to think clearly or make safe choices. Their physical coordination and mental functioning may also be impaired, which can put them at risk for accidents or injuries.[2]
When the effects of a substance wear off and it begins leaving the body, a person may experience withdrawal symptoms. These symptoms are typically very unpleasant and can include nausea and vomiting, diarrhea, excessive sweating, difficulty sleeping, muscle cramping, and significant mood changes. Withdrawal symptoms can range from uncomfortable to genuinely dangerous, depending on the substance and how long the person has been using it. The discomfort of withdrawal often drives people to use the substance again just to feel relief, which perpetuates the cycle of addiction.[2]
Beyond intoxication and withdrawal, there are behavioral and social signs that indicate a substance use disorder may be present. According to established diagnostic criteria, these signs include taking the substance in larger amounts or for longer periods than intended, having strong desires or urges to use the substance, making unsuccessful attempts to cut down or stop using, and spending considerable time obtaining the substance, using it, or recovering from its effects. A person with substance use disorder may have difficulty fulfilling their responsibilities at work, school, or home because of their substance use.[2]
Other important warning signs include continuing to use the substance even when it causes problems in relationships, giving up important social, work-related, or recreational activities because of substance use, using substances repeatedly even in dangerous situations, and continuing use despite knowing that it’s causing or worsening physical or psychological problems. As the disorder progresses, a person develops tolerance, meaning they need increasingly larger amounts of the substance to achieve the same effect they used to get with smaller amounts.[2]
Changes That Friends and Family May Notice
People close to someone with a substance use disorder may notice changes in the person’s personality, behavior, habits, and overall functioning. These changes often develop gradually but can become quite pronounced over time. The person may begin to isolate themselves from friends and family, withdrawing from social activities they once enjoyed. Their personality may seem different, with extreme mood swings, increased irritability, or unexplained sadness and anxiety, especially when they’re not using substances.[17]
Changes in daily habits and routines can also signal a problem. Someone with substance use disorder might start using substances first thing in the morning, or while at school or work. They may begin using alone rather than in social situations, and they might experiment with new types of drugs or start mixing different substances together to intensify the effects. Their choices of activities and friends may shift to revolve around substance use, and they may struggle with basic aspects of their life such as maintaining hygiene, managing money responsibly, or showing up for commitments.[17]
Physical health may decline, with decreased energy levels, unexplained injuries, or problems with memory and concentration. Academic or work performance often suffers, with declining grades or productivity, frequent absences, and difficulty completing tasks. Relationships become strained and tense, and the person’s self-esteem may visibly decrease. Financial problems may emerge as more money is spent on obtaining substances. These changes, taken together, paint a picture of someone whose life is being significantly impacted by problematic substance use.[17]
Prevention Strategies
While substance use disorder can affect anyone, there are strategies that can help reduce the risk of developing this condition. Prevention efforts are most effective when they address multiple aspects of a person’s life and begin early, before problematic patterns have a chance to develop.
Education plays a vital role in prevention. Learning accurate facts about different substances, including their short-term and long-term effects and their risks, helps people make more informed decisions. Understanding that some substances are highly addictive and can lead to loss of control after just one or two uses is important information that everyone should have, especially young people who may face pressure to experiment with drugs or alcohol.[17]
Building strong social connections and healthy coping skills provides protection against substance use disorders. When people have supportive relationships with family and friends, access to mental health resources when they’re struggling, and healthy ways to manage stress and difficult emotions, they’re less likely to turn to substances as a coping mechanism. Addressing underlying mental health conditions such as depression, anxiety, or trauma through proper treatment also reduces the risk of substance use disorders developing as a way to self-medicate these conditions.
For young people, delaying the age at which they first try alcohol or drugs significantly reduces their lifetime risk of developing a substance use disorder. Parents, schools, and communities can work together to create environments that discourage early substance use while providing young people with information, skills, and support they need to resist peer pressure and make healthy choices.
How Substance Use Disorder Affects the Body
Understanding the pathophysiology, or the changes in normal body functioning caused by substance use disorder, helps explain why this condition is so difficult to overcome without proper treatment. The changes occur primarily in the brain but can affect virtually every system in the body.
The brain’s reward system undergoes significant changes with repeated substance use. Normally, this system responds to pleasurable activities like eating good food, spending time with loved ones, or achieving goals by releasing dopamine, which creates feelings of satisfaction and motivation. When substances flood the brain with much larger amounts of dopamine than natural rewards would produce, the brain begins to adapt by reducing its own dopamine production or reducing the number of receptors that can receive dopamine signals.[2]
These adaptations mean that over time, everyday activities that used to bring pleasure no longer feel rewarding. The person needs the substance just to feel normal, and without it, they may feel flat, lifeless, and unable to enjoy anything. This is why someone with substance use disorder continues using despite negative consequences—their altered brain chemistry drives them to seek the substance to restore a sense of wellbeing, even temporarily.
The changes extend beyond the reward system to affect areas of the brain responsible for judgment, decision-making, learning, memory, and behavior control. This helps explain why people with substance use disorders often continue using even when they genuinely want to stop and understand the harm they’re causing. Their brain’s ability to regulate behavior and make decisions has been compromised by the physical changes caused by repeated substance exposure.[5]
Physical dependence develops when the body adapts to having the substance present and begins to rely on it for normal functioning. When the substance is suddenly removed or significantly reduced, the body goes into a state of distress, producing the uncomfortable and sometimes dangerous withdrawal symptoms described earlier. This physical dependence, combined with the psychological changes, creates a powerful trap that makes quitting extremely difficult without proper medical support and treatment.
