Many people abusing opioids experience “nodding,” a symptom of severe drowsiness resembling a person falling into a deep sleep, but really falling into a semiconscious state after taking drugs (commonly opioids like heroin or fentanyl). Nodding off is a dangerous, often involuntary, condition characterized by the head nodding forward while the person drifts between consciousness and sleep. Nodding may indicate a severe lack of oxygen and an excess of carbon dioxide preceding an overdose. New brain imaging data suggest that nodding could be contributing to damage in oxygen-sensitive brain areas. It’s important to know that opioid-overdose-related brain injuries resemble global hypoxic–ischemic brain injury, the same injury class seen after near-drowning, choking/asphyxiation, or cardiac arrest. All are primarily oxygen deprivation injuries.

Drug overdose deaths have dropped significantly, but remain unacceptably high. Interruptions in the drug supply chain and increased availability of naloxone for reversing overdoses have been major factors in progress. But for every fatal drug overdose, there are many more often ignored, non-fatal overdoses, and their immediate as well as cumulative effects are very dangerous. Opioid misuse and addiction, with and without overdoses, damage important memory centers in the brain. “On the nod” often represents subclinical overdose, and repeated episodes may contribute to cognitive impairment, neurocognitive consequences of repeated opioid-related hypoxia, cardiac arrhythmias, and brain injury anoxia, especially with fentanyl.

We know many overdoses aren’t reported, whether the rescued person overdosed at home or elsewhere, and took naloxone. In 2023, U.S. pharmacies dispensed 2.1-plus million naloxone prescriptions, a significant increase from earlier years (1.7 million in 2022).

According to Casillas et al., from 2010 through 2020, there was approximately one fatal overdose per 15 non-fatal overdoses. Thus, if roughly 80,000 people died annually from overdoses, total overdoses (fatal + non-fatal) likely exceeded 1 million annually.

NOT a Nice Nap

The nodding individual appears deeply asleep: The head droops forward, eyes close halfway, speech slows or trails off, and the body becomes slack and heavy. A person may briefly respond to their name or a touch, fading into silence moments later. Someone who arouses briefly but immediately nods off is not “safe.” Emergency medicine providers don’t and shouldn’t trust patients saying they’re “fine,” or receiving information like, “He always nods like this,” or “She’s just high.”

This is not normal sleep. Many describe it as a sensation of floating or slipping between wakefulness and rest. Nodding is often sought rather than perceived as the dangerous warning sign it is.

Opioids depress brain regions responsible for alertness and breathing. They also reduce brain responsiveness to carbon dioxide, which normally stimulates breathing and helps maintain wakefulness. As opioid levels rise, breathing becomes shallower, carbon dioxide levels increase, and sedation deepens. The person may appear fine; however, the body is under impaired respiratory control.

New studies show opioid use disorder (OUD) decreases oxygen availability, damaging brain cells, suggesting users cannot tell they’ve had an overdose. Opioid nodding through ODs causes persistent brain changes by interrupting oxygen delivery, not directly poisoning neurons. OUD itself is associated with smaller hippocampal volumes (replicated across multiple samples). There is credible evidence that an overdose can be a brain-injury event, even when “reversed,” and patients appear neurologically intact.

A nodding person on opioids may be arousable to voice or light touch, breathing slowly but steadily. As opioid effects deepen, the same individual may become difficult or impossible to awaken, breathing may slow further or become irregular, and blood oxygen levels may fall. From the outside, these changes appear subtle. But this person needs emergency treatment. Many people think that as long as a person still breathes, they are safe. This is not true.

In reality, opioid-induced breathing may be inadequate even when not stopping completely. Shallow or infrequent breaths can allow oxygen levels to drop without dramatic signs of distress. As oxygen falls and carbon dioxide rises, sedation deepens, creating a feedback loop leading to respiratory failure. Snoring, choking, or gurgling sounds, often mistaken for deep sleep, may indicate partial airway obstruction and worsening risk.

People using opioids may become accustomed to heavy sedation and feel safe because they “nodded” before without apparent harm. However, tolerance to the pleasurable/sedating effects of opioids may increase faster than the body’s tolerance to respiratory depression. This imbalance is especially pronounced with drugs like fentanyl as well as opioids combined with alcohol, benzodiazepines, xylazine, and/or medetomidine or other sedatives. As a result, a dose familiar to users can dangerously suppress breathing.

Addiction Essential Reads

Studies show hypoxia is worse during head-down posture (“nodding”)—hypoxia without collapse is common. Chronic opioid use is associated with central sleep apnea, blunted hypoxic drive, and impaired shortness of breath signals and arousal responses.

Oxygen saturation can fall without obvious distress. Affected people often aren’t cyanotic (blue). Bystanders may see no problem, but many “nodding” episodes meet criteria for mild-moderate opioid overdose. Hypoxia may occur even when the person is arousable.

Fentanyl and its analogs cause rapid, profound respiratory suppression and shallow breathing, and the margin between nodding and death is much narrower than in the heroin era. Fentanyl is often adulterated, containing xylazine or medetomidine. This makes hypoxia more likely. Medetomidine is significantly more potent than xylazine—100 to 300 times more—leading to deeper, longer-lasting sedation and hypoxia risks.

There is no safe intoxicated state once breathing is compromised

Sedation impairing ventilation is an overdose. In the operating room, anesthesiologists use opioids to blunt pain and suppress reflexes under controlled conditions. Surgical patients often receive oxygen supplementation and continuous monitoring. The anesthesiologist intervenes immediately if oxygen saturation or breathing drops by stimulating, ventilating, or reversing opioids.

In contrast, when opioids are taken outside medical settings, the main danger is respiratory depression—opioids blunt the brainstem’s responsiveness to increased CO₂ and low O₂. By the time a user realizes they are in distress, they may be unable to act. If prolonged, brain injury or death may occur. Opioid-induced respiratory depression causes breathing to become slow, shallow, and irregular, but these signs may be mistaken for falling asleep or snoring. Hypoxia can cause brain damage within minutes, even while the heart still beats

A user, alone or with peers, almost never has an anesthesiologist’s expertise, pulse oximeters, bag-mask ventilation capability, or naloxone to reverse a falling oxygen level. Pulse oximeters are inexpensive and easily purchased, but they are not part of the “drug use culture.”

In the future, wearable monitors combined with automatic alerts (such as smartwatches detecting hypoxia or a respiratory pause) could become harm-reduction tools—and work in this area is emerging. But it might not help with potent synthetic opioids (fentanyl and adulterants) because respiratory depression can become profound in under a minute—faster than a person can read or react to a monitor.

Conclusion

At the annual conference of the Community Anti-Drug Coalitions of America (CADCA) Conference on 2/26, General Barrye Price reminded everyone that it’s fantastic we have reduced opioid overdose deaths by at least 25 percent, but it’s equally important to remember that nearly 1 million overdoses per year occur. During my Lifetime Achievement acceptance remarks, I added that people using opioids are at very high risk for subtle to profound neurological consequences, as well as known problems associated with OUDs.