In 2020, over 1.5 million people had an opioid use disorder (OUD). One in five adults in the United States experiences some form of mental illness.[1,2] Mental illness and drug addiction commonly co-occur. About half of individuals with mental illness will also develop a substance use disorder, and half of those with a substance use disorder will also have mental illness.
The Connection Between Mental Health & Opioid Use
Of the nearly 39 million people in the United States with a mental health disorder, close to 20% also use prescription opioids, receiving nearly half of all opioids prescribed in the U.S. Mental health conditions increase the risk of developing OUD and vice versa.When two disorders, such as OUD and a mental health disorder occur in the same individual, it is called “dual diagnosis”. Mental health and medical professionals recognize the importance of treating mental health disorders at the same time as substance use disorders. These disorders can often be complexly intertwined, and treating them at the same time is critical.The following mental health disorders commonly co-occur with OUD and SUD:
Depression and OUD
Depression is a mood disorder of the brain involving brain chemicals and often genetic and environmental factors. It can cause feelings of sadness and poor motivation that interfere with daily life functioning. People with depression often turn to drugs as a form of self-medication to feel better, which raises the risk for developing a substance use disorder. Similarly, opioid use can lead to extreme mood swings and crashes when the drug wears off, which can cause depression. Depression and OUD commonly co-occur. Studies have shown as many as 41% of people with OUD also have a mood disorder.
Anxiety and OUD
Anxiety disorders also commonly co-occur with OUD, at rates as high as 43% in studies of people being treated for OUD. Similar to depression, anxiety is a disorder that can involve multiple genetic, environmental and biochemical factors that can increase the risk for substance use and abuse and therefore addiction. Close to one in three people with an OUD also experience either insomnia or anxiety.
OCD and OUD
OCD, or obsessive-compulsive disorder, includes obsessions (uncontrollable and recurring thoughts) and compulsions (repetitive behaviors). Risk factors for the disorder often overlap with risk factors for substance abuse and OUD. These include genetics, brain functioning, childhood trauma and environmental factors
Personality Disorders and OUD
Among the various types of personality disorders, the most common to co-occur with SUDs are antisocial personality disorder and borderline personality disorder. It is estimated that somewhere between 34.8% to 73% of people being treated for addiction also have a personality disorder. Typically, the personality disorder is the primary condition, and the substance use disorder develops as a result.
Bipolar and OUD
Bipolar disorder is defined as having periods of both depression and mania. It is estimated that approximately 56% of people with bipolar disorder also have a substance use disorder at some point in their lifetime. Bipolar disorder can include significant and extreme mood swings, which can be made more extreme by concurrent use of substances such as opioids.
Effect of Mental Health on Opioid Use
We do not often think of opioids as psychiatric drugs, but we probably should. Opioids bind to opioid receptors in the brain and cause feelings of pleasure — the euphoric “high.” This can increase the amount of mood enhancers, or brain chemicals called neurotransmitters that are responsible for feelings of pleasure, such as dopamine, in the brain. Therefore, they very much change the brain’s chemistry, and, with long term use, can alter a person’s behavior and personality. We really should think of them not only as pain medications, but as psychiatric medications as well. In someone with an underlying mental health disorder, opioids can either ameliorate or exacerbate the symptoms of various psychiatric conditions. It is no wonder that mental health conditions and OUD are so often seen together. Effective treatment of one requires effective treatment of the other. 
Effect of Opioid Use on Mental Health
Opioids change the chemistry in the brain and interact with the pleasure and reward receptors. This can cause extreme highs when taking the drugs and significant lows when they wear off. Because opioids create what can be thought of as a “fake” or artificial “euphoria” or happiness, depression and anxiety conversely are common side effects of opioid withdrawal. Prescription opioid use has been frequently associated with an elevated risk for also developing major depression. The more regularly opioids are taken, the more they change cellular function over time. This can mean that a person can no longer easily feel pleasure without the opioid drug. This causes repetitive opioid use and the development of OUD.