Short answer
Urine tests detect 11-nor-9-carboxy-THC (THC-COOH), a metabolite of THC. A standard screening cutoff is 50 ng/mL. A confirmation cutoff is 15 ng/mL. Detection windows run from 1 to 3 days after one use to 30 days or more in chronic heavy users.
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How a urine test finds THC
The body converts THC into THC-COOH. The liver makes this metabolite. Urine carries it out. Immunoassay screens bind to THC-COOH. A positive screen goes to gas chromatography-mass spectrometry (GC-MS) or liquid chromatography-tandem mass spectrometry (LC-MS/MS). The confirmation step identifies the molecule and its amount.
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Cutoff levels
Federal workplace testing uses a 50 ng/mL immunoassay cutoff. The confirmation cutoff is 15 ng/mL. Some labs use a 20 ng/mL screening cutoff. A result below the cutoff is negative. A result at or above the cutoff is positive. The cutoff sets the sensitivity of the test. Lower cutoffs find less metabolite. Higher cutoffs miss low-level exposure.
Detection windows by use pattern
Detection time depends on how much THC enters the body and how fast the body clears it. These ranges come from controlled studies and lab data.
Cannabis in Urine Test: How Long After Last Use and How to Choose a Test Kit
- Single use: 1 to 3 days.
- Moderate use (2 to 4 times per week): 3 to 7 days.
- Chronic heavy use (every day for months): 10 to 30 days. Some cases reach 60 days.
- High-potency concentrates (dabs, oils, edibles): longer than flower in many cases.
Factors that change detection time
- Dose and potency: flower runs 10% to 25% THC. Concentrates run 60% to 90% THC.
- Frequency: regular use builds a body burden of THC-COOH.
- Body fat: THC stores in fat tissue. Release is slow.
- Metabolism: liver enzyme activity, age, and genetics change clearance rates.
- Hydration: large water intake dilutes urine. Labs check creatinine to spot dilution.
- Sample timing: first morning urine holds more metabolite than a midday sample.
Sensitivity limits and false results
Immunoassays can cross-react with other compounds. Efavirenz (an HIV drug), ibuprofen, naproxen, and proton pump inhibitors can cause a false positive. Confirmatory GC-MS or LC-MS/MS resolves most false positives. False negatives come from diluted urine, low metabolite levels, or a high cutoff. A rapid urine test often uses 50 ng/mL. A lab test can use 15 ng/mL. A negative result does not prove zero THC use. A positive result at 15 ng/mL confirms THC-COOH.
What a urine test cannot tell
Urine tests do not measure impairment. They show past exposure. They cannot say when use happened or how much. Blood tests detect THC for 3 to 12 hours. Saliva tests detect THC for 1 to 24 hours. Urine holds the metabolite for the longest window.
Hemp, CBD, and positive tests
Hemp products with less than 0.3% THC can cause a positive urine test at high doses. CBD isolate has low risk. Full-spectrum hemp oil has higher risk. The amount of THC in the product and the dose drive the result.