How Long Does THC Stay in Blood?
Evidence-based answer reviewed against SAMHSA cutoffs and FDA assay documentation · Updated August 2026
Quick answer: Most people clear THC from blood within 12–24 hours of last use — heavy or daily use stretches that window substantially. Urine immunoassay screens for the metabolite THC-COOH at 50 ng/mL (initial) with GC–MS confirmation at 15 ng/mL (SAMHSA workplace standard).
THC detection windows by test type
Each specimen tells a different story because each samples different biology:
| Test type | Typical THC detection window |
|---|---|
| Urine | occasional: about 3 days · regular: 5–7 days · daily: 10–15 days · heavy: 30+ days in well-documented chronic heavy-use cases |
| Saliva (Mouth Swab) | occasional: 24 hours; regular: up to 72 hours; daily: up to 72 hours |
| Hair Follicles | up to 90 days (standard head-hair window) |
| Blood | occasional: 12–24 hours; regular: up to 2 days |
('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
Urine drug tests do not look for active THC. They look for THC-COOH, an inactive metabolite your liver produces after you consume cannabis in any form — flower, vape carts, dabs, or edibles. Because the metabolite is fat-soluble, it lingers far longer than the high itself, and there is no reliable way to predict an individual's exact clearance time from a chart.
Edibles and smoked cannabis produce the same THC-COOH metabolite, so a test cannot tell how you consumed it. Concentrates such as dabs deliver larger doses of THC, which tends to extend the detection window rather than shorten it.
Delta-8 and THCa products are chemically different from delta-9 but are converted to the same metabolites after use. Most workplace panels cannot distinguish them, so 'hemp-derived' labeling does not make a product test-safe.
Testing cutoffs in plain language
Urine immunoassay screens for the metabolite THC-COOH at 50 ng/mL (initial) with GC–MS confirmation at 15 ng/mL (SAMHSA workplace standard). 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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How long THC stays detectable in your system (all test types) — urine, hair, saliva & blood windows explained with cutoffs. Full guide →
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How Long Does Weed Stay in your Blood Drug Test?
Urine detection runs roughly about 3 days after last use; hair extends to ~90 days and saliva stays within 24–72 hours. Full breakdown in our detection guides.
How Long Does Thc Stay in Blood for Drug Test?
Urine detection runs roughly about 3 days after last use; hair extends to ~90 days and saliva stays within 24–72 hours. Full breakdown in our detection guides.
Can secondhand exposure cause a positive?
Practically impossible for cannabis smoke at modern cutoffs — the Johns Hopkins hot-box study found transient levels well under confirmatory thresholds. Edible ingestion is different.
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)