Quick answer
Cannabis clears a urine screen in about 3 to 30 days, a blood test in 1 to 2 days, a saliva test in 1 to 3 days, and a hair test in up to 90 days. The exact number depends on how often you use, how much THC you take in per session, your body fat, your metabolism, your hydration, and the cutoff level the lab applies. A one-time user often tests clean in a few days. A daily user can stay positive for a month or longer.
Detection windows by test type
Urine
Urine is the most common workplace screen. It looks for THC-COOH, a metabolite that leaves the body slowly because it stores in fat tissue. Occasional use shows up for roughly 3 to 7 days. Chronic, high-dose use can register for 30 days or more. Labs usually set a cutoff at 50 ng/mL for screening and 15 ng/mL for confirmation.
Blood
Blood measures delta-9-THC itself, not the long-lived metabolite, so the window is short. Peak levels appear within minutes of smoking and drop fast. Most people test negative within 1 to 2 days after a single use. Heavy daily users may still show THC for a few days.
Saliva (oral fluid)
Oral fluid tests are common in roadside and workplace settings because collection is quick and hard to fake. THC shows up within an hour of use. The window runs about 24 to 72 hours, and it stretches closer to 3 days with frequent use.
Hair
Hair tests reach back the furthest. THC deposits in the follicle as the hair grows, so a 1.5 inch sample can cover roughly 90 days. Hair grows about half an inch per month, which is why the timeline follows length.
What changes your window
- Frequency of use. Daily use saturates fat stores and slows clearance.
- Body fat percentage. More fat tissue means more storage and a longer release.
- Metabolism and age. Faster metabolisms clear metabolites sooner.
- THC potency. Concentrates and edibles deliver larger doses than flower.
- Hydration and activity. Diluted urine can drop a sample below the cutoff, though labs flag over-dilute samples.
- Test cutoff level. A 15 ng/mL confirmation cutoff catches more positives than a 50 ng/mL screen.
Before you run a home test
At-home kits are cheap and convenient, but they only work if you follow the timing rules the manufacturer set.
- Check the expiration date on the kit and confirm it matches the sample type you want.
- Read the full instruction sheet once before opening any pouch.
- Collect the sample exactly as directed, including the required volume or swab time.
- Start a timer the moment the sample meets the reagent.
- Read the result only inside the stated window, since lines that appear later are invalid.
- Record the result, the date, and the hours since your last use.
Reading and repeating a result
A faint line still counts as a negative on most strip tests. A negative result means the metabolite fell below the kit cutoff, not that THC has left your body. If you test again, wait at least 48 hours and use the same sample type so the two results compare. A single positive at-home result is a screening signal, not a diagnosis. Confirmation testing at a lab with mass spectrometry gives the number that matters for legal or employment purposes.