Short Answer

Detection windows depend on the test and the person. After one use: urine 1 to 3 days, blood 1 to 2 days, saliva 24 to 48 hours, hair up to 90 days. After months of daily use: urine 10 to 30 days or longer, blood up to 7 days.

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Window by Test Type

Urine

Urine tests measure THC-COOH, a metabolite made in the liver. That metabolite leaves the body in urine over days to weeks. Fat tissue stores it and releases it as fat burns.

How Long Does THC Stay in Your Body?

  • One use: 1 to 3 days.
  • Use 2 to 4 times per week: 5 to 7 days.
  • Daily use: 10 to 30 days.
  • Heavy daily use over years: 30 to 60 days in published case reports.

Blood

Blood tests measure THC itself, not just the metabolite. THC clears from blood in hours. Window: 1 to 2 days after one use, up to 7 days with heavy daily use. THC-COOH stays in blood longer than THC.

How Long Can Cannabis Be Detected in a Drug Test?

Saliva

Oral fluid tests pick up THC from recent smoke or vapor. Window: 24 to 48 hours. Some tests detect THC at 72 hours.

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Hair

Hair tests measure THC and THC-COOH bound in the hair shaft. Head hair grows about 0.5 inch per month. A 1.5 inch sample covers about 90 days. Body hair grows slower and covers a longer window.

Factors That Change the Timeline

  • Frequency and dose. Daily high-dose use extends every window.
  • Potency. Concentrates and high-THC flower carry more THC per dose.
  • Route. Edibles and oral products clear slower than inhaled smoke or vapor.
  • Body fat. THC is fat soluble, so more fat stores more metabolite.
  • Liver function and metabolism. Faster metabolism clears THC faster.
  • Age and hydration. Low water intake slows excretion.
  • Exercise and fat loss. Fat loss can push stored THC-COOH into blood and urine.

Cutoff Levels

Federal workplace urine testing uses a 50 ng/mL immunoassay screen. A sample above that level goes to a confirmatory test, GC-MS or LC-MS/MS, with a 15 ng/mL cutoff. Detection windows in studies shift with the cutoff. At a 20 ng/mL cutoff, more samples read positive and windows stretch out.

CBD, THC, and Drug Tests

CBD isolate holds no THC. Full-spectrum hemp extract can hold THC at 0.3% or less by dry weight under US law. Daily high-dose use of a full-spectrum product can build THC-COOH above a test cutoff. A certificate of analysis lists the THC content of a batch. Check the COA for total THC before you buy. A product with no COA gives you no number to check.

False Positives

Some drugs cross-react with urine immunoassays: efavirenz, some NSAIDs, proton pump inhibitors, and dronabinol. A positive screen is not a positive test. Confirmatory mass spectrometry rules out these cases.

Secondhand Smoke

Studies of non-smokers in closed rooms with heavy smoke found urine THC-COOH below 50 ng/mL in most cases. At a 20 ng/mL cutoff, some samples read positive.

What Is Not Known

No formula predicts one person's clearance date. Fat percentage, dose history, and cutoff interact. A lab test on your own sample is the same step a lab takes.