How Long Does Naltrexone Stay in Blood?
Evidence-based answer reviewed against SAMHSA cutoffs and FDA assay documentation · Updated August 2026
Quick answer: Most people clear Naltrexone from blood within ~1 day of last use — heavy or daily use stretches that window substantially. Never screened on standard panels; specialized adherence monitoring exists in treatment programs.
Naltrexone detection windows by test type
Each specimen tells a different story because each samples different biology:
| Test type | Typical Naltrexone detection window |
|---|---|
| Urine | any: 1–3 days (oral); injectable releases for weeks |
| Saliva (Mouth Swab) | any: ~1 day |
| Hair Follicles | rare |
| Blood | any: ~1 day |
('Blood testing measures ACTIVE circulation — closest proxy to impairment, shortest windows (hours-to-a-couple-days). Hospitals order it clinically; courts order it post-accident (DUI contexts); employers rarely bother given logistics and cost.',)
Why detection works this way
Naltrexone blocks opioid receptors rather than activating them — it's the opposite of an opioid in screening terms and appears nowhere on employment panels. Treatment programs may monitor levels to verify adherence to monthly injections.
Testing cutoffs in plain language
Never screened on standard panels; specialized adherence monitoring exists in treatment programs. A specimen under the initial cutoff reports negative without further work; a screen above cutoff gets confirmed by mass spectrometry before anyone sees a positive.
Planning ahead? Our at-home drug test guide covers retail kits that mirror lab screens.
Certified labs nationwide · Results in 1–2 days
Need a test? Order online, test same-day →People also ask
Does Naltrexone Show up on a Drug Test?
No — Naltrexone is absent from standard drug panels. Full guide →
Can Naltrexone Cause a False Positive Drug Test?
Can Naltrexone trigger a false positive? Cross-reactivity evidence, confirmation testing, and how to clear your name with the MRO. Full guide →
How Long Does Naltrexone Show up on a Drug Test?
How long Naltrexone stays detectable in your system (all test types) — urine, hair, saliva & blood windows explained with cutoffs. Full guide →
Naltrexone Drug Test Guide: Panels, Detection Windows & More?
Complete Naltrexone drug test guide: which panels detect it, urine/hair/saliva/blood detection windows, cutoff levels and prescription verification. Full guide →
Do prescriptions count against me?
No — verified prescriptions report as negative through the Medical Review Officer. Declare medications at collection and answer the follow-up call.
Sources & further reading
- SAMHSA — Mandatory Guidelines for Federal Workplace Drug Testing Programs (cutoffs, MRO process)
- DOT — 49 CFR Part 40 procedures for transportation workplace testing
- Brahm NC et al., Mayo Clinic Proceedings 2008;83(1):66–76 — false-positive cross-reactivity reference
- FDA — drug-of-abuse test device labeling (detection window conventions)