Fentanyl, Oxycodone, and Morphine: Study Identifies the Highest-Risk Opioid Painkillers

A new study by researchers at the University of Manchester has found that the risk of dangerous respiratory depression varies considerably among opioid pain medications. Compared with codeine, the highest risks were associated with fentanyl, combination opioid therapy, oxycodone, and morphine.

The findings, published in the journal BMC Medicine, are based on an analysis of medical records from more than 32,000 adults who received opioid treatment for non-cancer pain.

The researchers found that patients prescribed fentanyl were more than three times as likely to develop respiratory depression compared with those receiving codeine. The use of multiple opioids in combination nearly tripled the risk, while oxycodone and morphine were also associated with significantly higher rates of respiratory complications.

Even when compared directly with morphine, fentanyl remained the more hazardous option, with nearly twice the risk of respiratory depression.

The study also showed that higher opioid doses further increased the danger. Patients receiving at least 120 milligrams of morphine-equivalent dose per day had approximately double the risk of respiratory depression compared with those taking less than 50 milligrams daily.

Researchers emphasize that particular caution is needed when prescribing opioids to people with chronic lung diseases. Among patients with chronic obstructive pulmonary disease (COPD), fentanyl use was associated with a fourfold increase in the risk of breathing complications.

The risk was also higher when opioids were combined with other medications that affect the central nervous system. In particular, concurrent use of gabapentinoids—including gabapentin and pregabalin—significantly increased the likelihood of respiratory depression.

According to the researchers, although all strong opioids act on the same opioid receptors, they differ in how they affect the brain’s control of breathing. Fentanyl is considered especially dangerous because of its high potency and its rapid penetration into the brain, which can cause breathing to slow or stop more abruptly.

The authors stress that opioids remain essential medications for the treatment of severe acute pain. However, both physicians and patients should recognize that different opioid drugs and dosages carry different levels of risk. The findings may help improve prescribing practices and reduce the likelihood of serious, potentially life-threatening complications.

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