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Methadone Maintenance Treatment for Co-Occurring Severe Mental Illness and Opioid Use Disorders

By Molly Vencel, the research intern at the Treatment Advocacy Center, September 9, 2020

Methadone maintenance may be an effective treatment for people with co-occurring severe mental illness and opioid use disorder, according to a new study published in Schizophrenia Bulletin Open from researchers at McMaster University.  

While many with schizophrenia and other psychotic disorders lack access to mental health treatment, even fewer have access to treatment for co-occurring disorders. Opioid use disorder has reached crisis levels in recent years, but few studies have investigated the impacts on people with severe mental illness.  


People with psychotic disorders such as schizophrenia are typically excluded from programs investigating the efficacy and safety of treatments for opioid use disorder, despite more than one in four individuals with a severe mental illness having a co-occurring substance use disorder during their lifetime.  

While treatments for people with both disorders exist, research has been scarce. The researchers of the study sought to fill this gap by analyzing data from 20 outpatient clinics currently providing methadone maintenance treatment, a common treatment for opioid use disorder.  

Methadone maintenance treatment works by providing a safe alternative to illegal opioids to reduce cravings and withdrawal symptoms. It is an evidence-based practice first used in the 1960s and is shown to effectively reduce a person’s misuse of opioids. Now, researchers are primarily interested in program retention rates because methadone maintenance requires daily contact and engagement with treatment to be effective.  

A common myth is that those with psychotic disorders will not be able to engage with long-term treatment for drug use disorders. This is based on the general belief that people with co-occurring disorders have worse outcomes, and their psychotic symptoms will make drug use treatment nearly impossible. However, current data does not support this misconception.  

The researchers of the methadone maintenance study followed 415 individuals, 37 of whom had a psychotic disorder. Throughout the study, in addition to conducting interviews they tracked individual’s clinical diagnosis, antipsychotic prescriptions, demographic data and urine tests for methadone and other substances to determine treatment adherence.  


The Canadian researchers found no significant difference in age, gender or time in treatment for those with versus without severe mental illness. Most important, there was no difference in methadone maintenance treatment retention rates between the two groups. About 80% of both people with psychosis and people without psychosis remained in methadone maintenance treatment after one year. The study authors highlight that this finding directly contradicts the commonly held belief that those with psychosis will not be able to participate in traditional methadone maintenance treatment programs.  

Only 41% of those with a psychotic disorder were prescribed antipsychotic medication during the study period, according to the results. The authors hypothesize that this may be due to the complex nature of psychosis, substance use and substance-induced psychosis, resulting in a failure to identify and treat psychosis according to clinical guidelines.  

Researchers did not explore the cause for the low antipsychotic use; however, it is likely that many participants could have benefited from an antipsychotic prescription. Even with access to methadone maintenance treatment, people with co-occurring disorders need other mental health services to make a full recovery. However, access to concurrent treatment is lacking in the current services available for this population, the results suggest.

Limitations and further research

The study authors cautioned that this research only included people voluntarily seeking drug treatment, so results may not apply to people who lack insight or do not desire treatment. In addition, the study did not differentiate between active and controlled psychosis which could ultimately impact a person’s ability to engage in substance use treatment.  

Despite these limitations, this study provides support for including those with co-occurring psychosis and substance use disorders in opioid treatment programs. Future research should focus on how to incorporate substance use and mental health treatments into one program, so that people can have the best proven treatments that address their full needs.


  • Lamont, R., et. al. (2020). Psychosis and comorbid opioid use disorder: Characteristics and outcomes in opioid substitution therapy. Schizophrenia Bulletin Open.

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