How Long Does Naltrexone Stay in Your system (all test types)?
Evidence-based answer reviewed against SAMHSA cutoffs and FDA assay documentation · Updated August 2026
Quick answer: Most people clear Naltrexone from your system (all test types) within varies by usage pattern 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 |
('Detection windows differ dramatically by specimen type because each matrix captures different biology: urine accumulates EXCRETED metabolites for days, saliva traps recent parent-drug residue for hours-to-days, hair archives bloodstream exposure for months, and blood measures active circulation almost in real-time.',)
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.
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Do prescriptions count against me?
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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)