When people overdose on opioids, whether they wake up on their own or are revived by Narcan, many doctors assume they are fully recovered. This is a mistake because hypoxia (insufficient oxygen to the brain and body) occurs during overdose, yet often is undiagnosed. Many with opioid use disorder (OUD) experience multiple overdoses. Each overdose adds additional brain cell loss. Research suggests that significantly more evaluation, follow-up, and treatment than currently provided is needed by nearly all overdose patients.

A prepublication of a new study by McKinstry may be definitive enough to change how people with OUDs are treated, especially after overdose. This study showed that people with OUD had significantly smaller hippocampal volumes than healthy controls. In addition, hippocampal volumes were associated with past non-fatal overdoses. Overdose history did not separate OUD subgroups and hippocampal volume by prior overdoses, suggesting overdoses are commonly not recognized. Thus, OUD patients are likely suffering anoxic damage to the hippocampus.

By itself, a history of opioid overdose is associated with lower cognitive function, supporting the idea that major problems may persist even when the acute event appears “reversed.” This new study builds on 50-plus years of published literature on neurocognitive loss caused by damage to the hippocampus after opioid overdose. In 2024, Todaro et al. reported on neurological evidence that non-fatal opioid overdose causes oxygen deprivation injuries rather than mechanical injuries, as from head trauma. Notably, cerebral hypoxia/anoxia damage in OUD and overdose is produced by the same biological cascade seen in near-drowning cases, as well as choking/asphyxiation and cardiac arrest.

Unfortunately, most patient histories do not quantify the number of overdoses a patient has experienced (many patients with OUDs suffer multiple overdoses), the total life amount of naloxone doses/infusions, documented hypoxemia, the number of incidents when patients turned blue, and the use of co-ingestants (benzodiazepines, xylazine, alcohol) likely because physicians assume the revived OUD patient is “fine."

At first glance, near-drowning and opioid overdose appear fundamentally different emergencies. One involves water, aspiration, and........

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