Many individuals with a substance use disorder suffer from some type of mental disorder as well,1,2 while some having multiple substance use disorders. According to the 2015 National Survey on Drug Use and Health (NSDUH), of the 20.8 million people aged 12 or older who had a substance use disorder during the past year, about 2.7 million (13 percent) had both an alcohol use and an illicit drug use disorder, and 41.2 percent also had a mental illness.3 Particularly striking is the 3- to 4-fold higher rate of tobacco smoking among patients with schizophrenia and the high prevalence of co-existing alcohol use disorder in those meeting criteria for Post-Traumatic Stress Disorder (PTSD). It is estimated that 30-60 percent of patients seeking treatment for alcohol use disorder meet the criteria for PTSD,4,5 and approximately one third of individuals who have experienced PTSD have also experienced alcohol dependence at some point in their lives.
The reasons why substance use disorders and mental disorders often occur together are not clear, and establishing the relationships between these conditions is difficult. Still, three possible explanations deserve attention. One reason for the overlap may be that having a mental disorder increases vulnerability to substance use disorders because certain substances may, at least temporarily, be able to reduce the symptoms of the mental disorder and thus are particularly reinforcing the need to use in these individuals. Second, substance use disorders may increase vulnerability for mental disorders,6-8 meaning that the use of certain substances might trigger a mental disorder that otherwise would have not occurred. For example, research suggests that alcohol use increases risk for PTSD by altering the brain’s ability to recover from traumatic experiences.9,10 Similarly, the use of marijuana, particularly marijuana with a high THC content, might contribute to schizophrenia in those who have specific genetic vulnerabilities.11 Third, it is also possible that both substance use disorders and mental disorders are caused by shared, overlapping factor such as particular genes, neurological deficits, and exposure to traumatic or stressful life experiences. As these possibilities are not mutually exclusive, the relationship between substance use disorders and mental disorders may result from a combination of these processes.
Regardless of which one might influence the development of the other, mental and substance use disorders have overlapping symptoms, making diagnosis and treatment planning particularly challenging. For example, people who use methamphetamine for a long time may experience paranoia, hallucinations, and delusions that may be mistaken for symptoms of schizophrenia, and the psychological symptoms that accompany withdrawal, such as depression and anxiety, may be mistaken as simply part of withdrawal instead of an underlying mood disorder that requires independent treatment.
Given the prevalence of co-occurring substance use and mental disorders, it is critical that addiction treatment professionals perform a comprehensive medical and psychological evaluations in order to provide the effective treatment programs that will treat both conditions.
Material Above is Courtesy of: The Surgeon General's Report on Alcohol, Drugs, and Health