Naltrexone and Routine Toxicology Screens
Naltrexone does not produce a positive result on standard routine toxicology screens for drugs of abuse. 1
Key Testing Information
The FDA label explicitly states that naltrexone does not interfere with standard drug detection methods, including thin-layer, gas-liquid, and high-pressure liquid chromatographic methods used to detect morphine, methadone, or quinine in urine. 1
Naltrexone may or may not interfere with enzymatic methods for opioid detection depending on the specific test's methodology—you must consult the test manufacturer for details about their particular assay. 1
Standard drug screening panels do not include naltrexone as a tested substance, so it will not be detected on routine toxicology screens. 2, 3, 4
Critical Exception: False-Positive Oxycodone Results
However, there is one important caveat: Naltrexone has a minor metabolite called noroxymorphone that can cause a false-positive result specifically for oxycodone on immunoassay screening tests. 5, 6
When This Occurs:
This false-positive occurs with oral naltrexone administration, not the extended-release injectable formulation. 5
Noroxymorphone is a lesser-known metabolite of naltrexone that is also the final intermediate in oxycodone's metabolic pathway, leading laboratories and clinicians to incorrectly assume oxycodone use. 5, 6
Individual pharmacogenomics can result in detection of noroxymorphone alone without other oxycodone pathway intermediates. 6
How to Manage This:
Request confirmatory testing using gas chromatography-mass spectrometry (GC-MS) when a patient on oral naltrexone has a positive oxycodone screen. 5, 7
Confirmatory testing will identify noroxymorphone specifically and rule out actual oxycodone use. 5
The American Academy of Pediatrics recommends never making consequential decisions based solely on immunoassay results without confirmatory testing, as screening tests are presumptive only. 2
Clinical Bottom Line
For routine toxicology monitoring in patients taking naltrexone:
Naltrexone itself will not trigger positive results for opioids, amphetamines, benzodiazepines, cannabinoids, or other standard drug classes. 1
The only documented false-positive is for oxycodone due to the noroxymorphone metabolite. 5, 6
Always obtain confirmatory GC-MS testing before taking any action on an unexpected positive oxycodone result in a patient prescribed oral naltrexone. 5, 7
This issue has devastating potential consequences including program termination and relapse if not properly recognized and confirmed. 6