People who have mental illnesses are twice as likely as the rest of the population to engage in substance abuse. At the same time, people who struggle with substance abuse are also more likely to develop a mental illness or behavioral disorder. It’s an accepted fact that mental illness can lead to substance abuse, and that addiction can cause other mental illnesses.
Dual diagnosis is far more common now than it used to be. At one point, mental illness and addiction would be treated as separate conditions. A person with depression or bipolar disorder would be referred to a mental health facility.
Someone addicted to alcohol or drugs would be referred to an addiction rehab center. The problem with this approach is both conditions often did not receive adequate treatment.
For example, a patient in rehab might be discharged for not responding to treatment due to their mental disorder. Meanwhile, a person in a mental health facility might be prescribed medication to treat their disorder, but their addiction to drugs or alcohol ends up interfering.
It’s easy to see why both conditions are now treated at the same time as co-occurring disorders at most addiction treatment centers.