Beauregard 2024: naltrexone and a false-positive oxycodone drug test

What they tested

The report describes one outpatient being treated with naltrexone tablets for alcohol use disorder and cannabis use disorder. His urine drug screens, quick tests that look for classes of drugs, came back positive for oxycodone more than once.

His clinicians ordered confirmatory urine testing, a more precise lab method that identifies specific substances. They also did a naloxone challenge, giving a short-acting opioid blocker to look for withdrawal signs that would point to recent opioid use.

What they found

Confirmatory testing detected noroxymorphone, a metabolite of naltrexone, and the authors concluded it caused the false-positive oxycodone result. The naloxone challenge was negative.

He then switched from naltrexone tablets to the extended-release injection and tolerated the change.

The body breaks naltrexone down mainly into 6-β-naltrexol, with two minor metabolites. Noroxymorphone is one of the less familiar ones, and this case shows it can show up on testing.

Limits

• It describes a single person, so it can't say how often this happens.
• The abstract doesn't name the screening test used, and the naltrexone labels note that interference depends on the test.

What it means if you're considering naltrexone

For someone on naltrexone who gets an unexpected positive opioid screen, this case shows that the medicine itself can, rarely, be the cause. Confirmatory lab testing can tell a naltrexone metabolite apart from oxycodone, which matters when drug test results have real consequences.