Editorial Director, Addiction & Recovery · Last reviewed January 2025
Substance use disorders (SUDs) are characterized by a problematic pattern of using a substance that leads to significant impairment or distress. The DSM-5 classifies SUDs on a severity spectrum — mild, moderate, or severe — based on the number of diagnostic criteria met. These criteria include impaired control over use, social impairment, risky use, and pharmacological criteria (tolerance and withdrawal).
According to the 2021 NSDUH, approximately 46.3 million people aged 12 or older in the United States met criteria for at least one substance use disorder in the past year. Alcohol use disorder is the most prevalent, followed by cannabis use disorder and opioid use disorder.
This section provides clinical overviews of the major substance use disorders — their neurobiological mechanisms, diagnostic criteria, medical consequences, and evidence-based treatments. For information on addiction recovery pathways, treatment levels, and family support, see the Addiction Recovery section. For information on the mental health conditions that frequently co-occur with substance use disorders, see our Co-Occurring Disorders section.
Overview by Substance
The Importance of Co-Occurring Disorders Assessment
All substance use disorders should be evaluated for co-occurring mental health conditions. Research consistently shows that 40–60% of individuals with SUDs have at least one co-occurring psychiatric disorder. Treating the addiction without addressing the underlying or co-occurring mental health condition produces substantially worse outcomes than integrated treatment. See our co-occurring disorders section for detailed resources on dual diagnosis treatment.
Related: Addiction Recovery · Co-Occurring Disorders · Medication-Assisted Treatment