How long does THC stay detectable?
Detection time depends on the test, not on the drug alone. Urine tests look for THC-COOH, a THC metabolite. A single use clears urine in 1 to 3 days. Daily use can show up for 30 days or more. Blood clears faster than urine. Saliva clears fastest. Hair keeps the longest record, about 90 days per 1.5 inch strand.
Detection times by test type
Ranges below come from lab data and federal workplace testing guidelines. Body fat, liver enzymes, dose, and product potency shift each number.
Urine
- One-time use: 1 to 3 days
- Occasional use, 2 to 4 times weekly: 3 to 7 days
- Daily use: 10 to 30 days
- Heavy chronic use with high body fat: 30 to 77 days in some studies
Urine holds THC-COOH longer than any other fluid except hair. A 2021 study of chronic users found detectable levels past 30 days in 3 of 10 subjects.
Blood
- One-time use: 1 to 2 days
- Weekly use: 2 to 7 days
- Heavy chronic use: up to 25 days in some reports
Blood measures active THC, not just metabolites. Levels peak within 10 minutes of smoking and drop fast.
how long does cannabis stay in your blood
Saliva (oral fluid)
- After smoking: 1 to 24 hours
- After edibles: up to 48 hours
- Heavy use: up to 72 hours
Oral fluid tests use a 4 ng/mL screen cutoff under federal rules. Confirmatory testing uses 2 ng/mL.
Hair
- Head hair: about 90 days per 1.5 inch (3.8 cm) segment
- Body hair: longer window, slower growth
- Federal hair cutoff: 0.1 ng/mg THC-COOH
Head hair grows about 0.5 inch (1.3 cm) per month. Labs cut a 1.5 inch sample near the scalp to cover the last 90 days.
What changes the window
- How often you use
- THC dose per session
- Product potency, including concentrates above 70% THC
- Body fat percentage
- Liver enzyme activity and metabolism
- Age
- Hydration and urine dilution
- Test cutoff level at the lab
Frequency and dose matter most. A person who uses once absorbs less THC than a person who dabs daily.
Cutoff levels
Federal urine testing screens at 50 ng/mL with an immunoassay. Any sample above that line goes to gas chromatography mass spectrometry. The confirmation cutoff is 15 ng/mL. A sample between 15 and 50 ng/mL fails confirmation even if the screen was negative.
Labs also run validity checks. Creatinine below 20 mg/dL and specific gravity below 1.003 flag a diluted sample. Diluted samples count as refusals in federal programs.
False positives
Some drugs cross-react with THC immunoassays. Reported cases include efavirenz, certain NSAIDs, proton pump inhibitors, and high-dose CBD products. Hemp products sold in the US can carry trace THC. Confirmatory mass spectrometry separates these cases.
Passive smoke exposure rarely pushes urine above 50 ng/mL. A 2015 review found no confirmed case from secondhand smoke in an open room.
State law
Detection windows are chemistry. Employer and legal rules are separate. As of 2025, 24 states and Washington DC limit employer action on pre-employment cannabis tests. Check your state labor agency for current rules.