Naltrexone is a specific opioid antagonist used to treat opioid and alcohol use disorder; it blocks opioid receptors and, in alcohol use disorder, reduces craving by blunting reinforcement. It is given orally (ReVia, Depade) or as a monthly IM depot (Vivitrol). Monitoring by LC-MS/MS confirms adherence, measuring naltrexone and its major metabolite 6-beta-naltrexol.1
Unlike agonist therapies, naltrexone provides no reinforcing effect, so adherence is a common challenge, especially with daily oral dosing; the monthly depot (Vivitrol) was developed partly to address this. Confirming naltrexone presence documents adherence between visits.2
Naltrexone is an antagonist and does not appear on opioid panels; a dedicated LC-MS/MS test measures naltrexone and 6-beta-naltrexol, with detection above a 10 ng/mL cutoff.3 A positive confirms recent adherence; with the monthly depot, interpret against the injection date, since urinary detection of oral dosing is only 1 to 2 days.
Confirms adherence. Naltrexone and/or 6-beta-naltrexol above cutoff indicates recent use.
Depot timing matters. With Vivitrol, interpret against the injection date, not only the short oral window.
Not an opioid result. A naltrexone positive reflects the antagonist, not opioid use.
Suggests non-adherence (oral). In a patient on oral naltrexone, absence suggests missed doses.
Short urinary window. Oral dosing is detectable ~1 to 2 days; timing affects the result.
Timing and cutoff. Absence may reflect timing of last dose or levels below the 10 ng/mL cutoff.
Naltrexone analytes measured on definitive testing.
| Metabolite | Clinical Significance |
|---|---|
| Naltrexone (parent) | Opioid antagonist; oral half-life ~8 to 10 h. |
| 6-beta-naltrexol | Major urinary metabolite; the main glucuronide-conjugated marker. |