Response to an opioid antagonist does not test every substance in a mixed exposure.
In an emergency-department toxicology investigation, illicit benzodiazepines were detected in twenty-one suspected opioid-overdose patients. Opioids were also common, and some patients with documented naloxone response showed no initial improvement.
The selected sample was small and lacked a controlled dose-response comparison. Nonresponse may have several explanations, including timing and other exposures; it does not independently identify a benzodiazepine.
Separate breathing, consciousness and subsequent clinical course when describing response. The report supports considering co-exposure, while naloxone nonresponse alone cannot exclude an opioid or establish which additional drug caused persistent symptoms. Definitive testing and the full treatment record remain important.
Source: PMC8389390, supplied full-text paper. Findings are paraphrased; forensic implications are an interpretation.
Related: Valproate After Benzodiazepines: Why a Pooled Status-Epilepticus Response Rate Needs Context.