Employment drug screens look for THC and its breakdown products, not the plant itself. A urine test detects 11-nor-9-carboxy-THC (THC-COOH), a metabolite the liver produces. An oral fluid test detects THC. A hair test detects THC and THC-COOH. The result depends on the specimen, the cutoff level, and the THC amount that entered the body.
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What the lab measures
Most US employers use a two-step process. An immunoassay screen runs first. A reading above the cutoff goes to a confirmatory test run with gas chromatography-mass spectrometry (GC-MS) or liquid chromatography-tandem mass spectrometry (LC-MS/MS). The confirmatory step identifies the molecule by mass, so it separates THC from compounds with a similar shape.
Federal workplace testing under SAMHSA rules uses these cutoffs: urine immunoassay 50 ng/mL, urine confirmation 15 ng/mL, oral fluid screen 4 ng/mL, oral fluid confirmation 2 ng/mL.
What Does Employment Drug Screening Detect for Cannabis? A Clear Guide
Detection windows by specimen
- Urine: 1 to 3 days after one use. 5 to 7 days after several days of use. 30 days or longer in chronic heavy users. THC-COOH is fat-soluble, so it clears at a slow rate.
- Oral fluid: 24 to 48 hours. Some tests reach 72 hours.
- Blood: 3 to 12 hours for THC, longer for THC-COOH.
- Hair: up to 90 days. Hair grows about 0.5 inches per month, and THC deposits in the shaft.
CBD and hemp products
CBD isolate holds no THC, so it does not create THC-COOH. Full-spectrum hemp extract can contain up to 0.3% THC by dry weight under US law. One dose carries a small THC amount. Repeated use of a full-spectrum product can build a urine level above 50 ng/mL in some people. Third-party lab reports list the THC content of a batch. Delta-8 THC, delta-10 THC, and HHC products break down into the same THC-COOH, so they can produce a positive result.
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False positives
The immunoassay screen can bind to other compounds. Reported cross-reactants include ibuprofen, naproxen, efavirenz, pantoprazole, and dronabinol. A confirmatory test resolves most of these cases. A screen positive is not the same as a confirmed positive.
Legal status and employer policy
State cannabis laws do not change federal testing rules. The Department of Transportation tests safety-sensitive workers under 49 CFR Part 40. Employers in states with recreational cannabis can still set a zero-tolerance policy, refuse to hire, or end employment after a positive result. Some states, including Nevada and New York, restrict pre-employment THC testing, with exemptions for safety-sensitive roles and federal contractors.