People living with severe mental illness who depend on opioids drop out of opioid agonist treatment at much higher rates than those without the condition. That is the headline finding from a major population-based study published in Drug and Alcohol Dependence. Researchers followed more than 14,700 people in New South Wales, Australia, over 14 years and found that severe mental illness significantly undermines treatment retention, especially in the earliest stages. The stakes are high. Without continued engagement, the risk of death rises sharply.

What the Research Examined

Researchers from the National Drug and Alcohol Research Centre at UNSW Sydney tracked everyone who entered opioid agonist treatment for the first time between 2006 and 2017. Opioid agonist treatment typically involves prescribing methadone or buprenorphine. Clinicians regard it as the gold standard for opioid use disorder. It reduces opioid use and lowers the risk of death.

The team defined severe mental illness as a psychotic or bipolar disorder. This included schizophrenia, schizoaffective disorder, and bipolar affective disorder. Of the 14,763 people in the cohort, around 13.5% had evidence of severe mental illness either before or during the follow-up period.

Researchers used multivariable Cox regression models to assess how severe mental illness affected treatment cessation and all-cause mortality. They controlled for age, sex, socioeconomic status, incarceration history, and physical health conditions.

Opioid Treatment Retention Suffers Most in Early Episodes

People with severe mental illness were considerably more likely to stop opioid agonist treatment. In the first treatment episode, their cessation rate ran 16% higher than those without the condition.

Looking across the first five episodes told a richer story. The gap was widest at the very start. Cessation rates ran 19% higher in the first episode and 13% higher in the third. By the fourth and fifth episodes, the difference had largely closed. People who stayed engaged over multiple episodes appeared to stabilise.

The authors believe this early vulnerability reflects the added complexity of managing two serious conditions at once. The intensive clinical contact typical at the start of opioid agonist treatment may be particularly valuable for people with co-occurring severe mental illness. More contact means more opportunities to catch and address problems before someone walks away.

The Mortality Picture

A total of 763 people (5.2% of the cohort) died during follow-up. Nearly a quarter of those deaths involved someone with severe mental illness.

Severe mental illness pushed all-cause mortality risk up by 35%. This fits with existing evidence that people with severe mental illness in the general population die at more than twice the rate of those without it. Schizophrenia alone links to 13 to 15 years of potential life lost.

Being in opioid agonist treatment, however, cut mortality risk sharply. On average, people in treatment were 76% less likely to die than those out of treatment. That protective effect was strongest in the early months and gradually eased over time.

Here is where the findings get nuanced. When researchers tested whether opioid agonist treatment benefited people with severe mental illness differently from those without it, they found no meaningful difference. Treatment reduced mortality risk by a similar margin in both groups. The problem is that people with severe mental illness start from a far higher baseline. So even with the same proportional benefit, their overall mortality remains elevated. Treatment is necessary but not sufficient on its own.

Why Early Support Around Opioid Agonist Treatment Matters

The researchers make a direct case for acting early. The window around a person’s first entry into opioid agonist treatment is where services have the greatest chance to reduce dropout and ultimately save lives.

Mental health screening at treatment entry is essential. The study found that 7% of the cohort only received a severe mental illness diagnosis during follow-up. They entered treatment without anyone knowing what they were dealing with. Earlier identification creates more room for appropriate support.

Integrated care models, where mental health and substance use services operate in close coordination, offer one practical answer. Evidence suggests these approaches improve symptom management and keep people in treatment for longer. Yet the treatment gap remains wide. A 2019 US study found that fewer than one in three people with both severe mental illness and opioid use disorder received treatment for both conditions in the same year.

The Broader Stakes

Physical health comorbidities are common in people with severe mental illness. Cardiovascular disease and diabetes both drive up mortality risk. Opioid agonist treatment alone does not address these conditions. The authors call for more comprehensive interventions that cover physical health alongside mental health and substance use support.

Methadone produced the highest retention rates in this cohort, consistent with earlier research from the same setting. Its full agonist profile and more frequent dosing schedule may make it a better fit for people with more complex clinical presentations.

Strengths and Limitations

The study draws on 14 years of linked population-wide data covering hospital records, mental health ambulatory data, criminal justice records, and the National Death Index. That breadth gives the findings real weight. Examining mortality and retention together, rather than separately, also moves the evidence base forward.

The authors note some caveats. The results come from one Australian state and may not apply to other countries or systems with lower opioid agonist treatment coverage. The data did not capture homelessness or childhood trauma, both of which shape treatment outcomes. Some people with undiagnosed severe mental illness likely landed in the group without a diagnosis. That would mean the study underestimates the true associations, so the findings lean conservative.

Looking Ahead

People with severe mental illness who depend on opioids need more than a prescription. They need coordinated, sustained support across mental health and substance use services, ideally starting from the first day of treatment. That means routine screening for severe mental illness at treatment entry, better links between services, and enough clinical contact in those early weeks to catch problems before they lead to dropout.

The evidence is now clear that failing to act early costs lives. And for a population already carrying an elevated mortality burden, early action around opioid agonist treatment is one of the most practical levers available to services today.

Source: dbrecoveryresources