The findings, published in Drug and Alcohol Dependence, compared brain scans from people with opioid use disorder (OUD) to people without a substance use disorder and found the hippocampus, the brain region most associated with memory, was measurably smaller in those with OUD.
For anyone researching addiction treatment, the finding underscores why getting into evidence-based care matters: opioid use disorder itself appears to take a measurable toll on the brain, and treatment is what interrupts that exposure.
What the Study Found
Researchers compared brain scans from 94 people with opioid use disorder and 40 people without a substance use disorder. People with OUD had significantly smaller hippocampal volumes in both hemispheres than controls.
The effect was strongest in the posterior, or back, portion of the right hippocampus, the region researchers say is more involved in retrieving the specific details of a memory and in spatial navigation. Differences in the front portion of the hippocampus did not hold up after statistical correction.
The researchers describe this as evidence that chronic exposure to opioids, the defining feature of opioid use disorder, may be associated with hippocampal vulnerability, building on years of animal studies showing similar limbic system effects.
A Closer Look at Treatment Subgroups
In an exploratory part of the analysis, researchers also compared hippocampal volumes among OUD participants based on which medication, if any, they were taking for treatment.
Participants on methadone showed smaller posterior hippocampal volumes than both the control group and participants on buprenorphine.
The study authors were explicit that this difference should not be read as evidence that methadone itself shrinks the brain.
They noted that people receiving methadone versus buprenorphine treatment often differ in ways the study could not measure and adjust for.
This included how severe their opioid use disorder is, how much opioid exposure they have accumulated over time, trauma history, and other life circumstances.
In other words, the subgroup difference likely reflects differences in the underlying addiction and its severity among the patients each medication tends to be prescribed to, not an effect of the medication itself. The authors called for further research to clarify what is driving this pattern.
Memory and Hippocampal Volume
In a smaller group of participants who also completed memory testing, larger hippocampal volume was linked to better memory accuracy among the control group.
That same link did not hold among participants with OUD, suggesting the usual relationship between brain structure and memory performance may work differently in people with opioid use disorder. The researchers note this finding is preliminary, given the modest sample size used for memory testing.
What This Means for Treatment Seekers
This research does not suggest that medication-assisted treatment should be avoided or that one medication is unsafe compared to another.
Methadone and buprenorphine remain the standard of care for opioid use disorder, and untreated opioid use disorder carries its own well-documented risks to the brain and body, including overdose.
The clearest takeaway from this study is that the addiction itself, through chronic opioid exposure, is what the researchers connect to smaller hippocampal volume, which reinforces the importance of starting treatment and stopping that exposure as early as possible.
If you are researching treatment for yourself or a loved one, this is a good moment to ask a provider how methadone and buprenorphine differ, including dosing, supervision requirements, and how a treatment plan will be tailored to your history and severity of use.
Exploring Treatment Options
Choosing the right addiction treatment program involves more than picking a medication. A few next steps worth considering:
- Compare opioid treatment programs that offer both methadone and buprenorphine so you can discuss which fits your situation
- Understand insurance coverage for addiction treatment before committing to a program
- Ask providers how they monitor patients on medication-assisted treatment over time
- Verify a facility’s credentials and treatment approach before enrolling
If you or a loved one is struggling with opioid addiction, you can search Rehab.com’s directory to find verified rehab centers nationwide. Call
800-985-8516
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to speak with a treatment advisor.
