The first few months matter most, and that is exactly when extra support is needed. Researchers found that people with a severe mental illness were significantly more likely to drop out of opioid treatment early, and faced a higher risk of death overall.
The study followed 14,763 people who started opioid agonist treatment (OAT) for the first time in New South Wales, Australia, between 2006 and 2017, linking their treatment records to hospital, mental health, and mortality data. It was published in Drug and Alcohol Dependence.
What the Study Found
Among the group, 13.5% had a severe mental illness, defined as a psychotic or bipolar disorder. During a person’s first treatment episode, those with severe mental illness had a 16% higher rate of stopping treatment than those without.
The gap was concentrated early. Dropout risk was higher in the first and third treatment episodes, then leveled off, with no meaningful difference by the fourth episode.
In other words, once people got past the initial period, they stayed in care at rates similar to everyone else.
Severe mental illness was also linked to a 35% higher risk of death from any cause during the study.
Staying in opioid treatment cut that risk sharply, and people with severe mental illness benefited from that protection just as much as people without it.
Why Opioid Treatment Retention Matters
Opioid agonist treatment uses methadone or buprenorphine, both long-acting medications that ease cravings and withdrawal so a person can stabilize.
It is considered the gold-standard treatment for opioid use disorder because strong evidence shows it reduces opioid use and lowers the risk of death.
The study reinforced that protective effect. Being in treatment was associated with an average 24% of the mortality risk seen when out of treatment, and the benefit was strongest early on.
That is why staying in care, especially in the first weeks and months, is so important, and why early dropout is so costly.
The Role of Dual Diagnosis
When a substance use disorder and a mental health condition occur together, clinicians call it a co-occurring disorder, or dual diagnosis.
The two often interact: untreated psychiatric symptoms can make it harder to stay in addiction treatment, and the conditions share roots such as trauma and social disadvantage.
The researchers noted that people with severe mental illness often face added hurdles, including fragmented services that treat mental health and addiction separately, distrust of providers and more complex health needs.
They pointed to a 2019 US study finding that fewer than a third of people with both a severe mental illness and opioid use disorder received treatment for both conditions in the prior year.
What the Researchers Recommend
The authors argue that the strongest opportunity to help comes at the very start of addiction treatment.
They call for detailed mental health assessments and screening for severe mental illness, paired with enhanced case management and better coordination between addiction and mental health services.
They also caution that medication alone may not be enough. Because people with severe mental illness carry a higher baseline risk of death, partly from physical conditions like heart disease and diabetes, the authors say care should also address those physical health needs, not just the addiction.
The study has limits. It drew on one Australian state, so results may not transfer directly to other health systems, and it relied on clinical records that can miss milder cases.
The authors note that any under-counting of mental illness would make their findings conservative rather than overstated.
What This Means for Treatment Seekers
If you or a loved one is entering drug rehab for opioids and also living with a mental health condition, this research is a reason to seek programs built for both.
Ask whether a facility screens for mental illness at intake, offers integrated dual diagnosis care, and provides intensive support during the first months, when the risk of dropping out is highest.
Finding the Right Rehab
Choosing among treatment options is easier when you know what to look for. When comparing rehab centers, consider whether they offer medication-assisted treatment with methadone or buprenorphine, integrated care for co-occurring mental health conditions, and strong early-engagement support.
It also helps to verify a facility’s credentials and confirm your insurance coverage for addiction treatment before committing.
Rehab.com’s directory includes verified rehab centers you can compare by location, level of care and specialty. Call
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