The short answer: after a single use, THC usually clears urine in about 3 days and blood in 1 to 2 days. Daily or heavy use stretches the urine window to 10 days and often 30 days or more. Saliva runs 1 to 2 days. Hair holds on for roughly 90 days. Your own number depends on how much you use, how often, your body fat, your metabolism, and how sensitive the test is. Nobody can hand you an exact date, and anyone who promises one is guessing.
Detection windows by test type
- Urine: the most common workplace test. Occasional use typically shows for up to 3 days. A few times a week, expect 5 to 7 days. Daily use for months, especially concentrates or high-dose edibles, can show for 10 to 30 days, and published cases have run longer. Urine tests look for the metabolite THC-COOH, not THC itself.
- Blood: a short window. NIDA puts it at 1 to 2 days after last use, though heavy users may still show something around 4 days in some studies. Blood tests measure actual THC, so they are better at catching recent use.
- Saliva (oral fluid): 24 to 48 hours, sometimes up to 72 hours in heavy users. Popular for roadside and workplace screening because collection is simple.
- Hair: up to 90 days for a standard 1.5 inch sample. Hair grows about half an inch per month, so the test reads like a timeline. Very long hair can carry older history.
- Nails and sweat: less common, and the windows vary widely. Treat anything you read about them as approximate.
Why the range is so wide
- Frequency and dose. A 5 mg edible once is not the same as daily dabs.
- Body fat. THC and its metabolites are fat-soluble, get stored in fat tissue, and are released slowly over time.
- Metabolism and liver enzymes. CYP2C9 and CYP3A4 activity varies a lot from person to person.
- Age, hydration, and kidney or liver function.
- Test cutoff. Federal workplace urine testing screens at 50 ng/mL and confirms positives at 15 ng/mL by GC/MS. A screen can come back positive while the confirmation comes back negative, which is why labs retest.
CBD products and drug tests
This is the part people get wrong. Full spectrum CBD can carry trace THC, and a daily high dose of full spectrum oil can build up enough to trip a screen. Isolate and THC-free broad spectrum products are lower risk, but no label is a guarantee unless there is a batch COA with actual THC results. Hemp-derived delta-8, delta-9, and THCA products will show up on a test. I look for a certificate of analysis that lists THC content and the lab's accreditation before I trust the words "THC-free" on the front of a bottle.
Secondhand smoke rarely triggers a positive at those cutoffs, but it is not zero, especially in a closed car.
THC Effects on Body and Mind: What You Need to Know
What helps and what doesn't
Nothing you can buy reliably beats a lab test. Water loading can dilute a sample, which many labs flag as negative-dilute or invalid, and drinking extreme amounts of water can be dangerous. Niacin, vinegar, bleach, and detox teas either do nothing or cause harm. Time and lower body fat are the only things that genuinely move the number, and you do not control both.
If you have a test coming and you used in the last month, the honest move is to plan around a possible positive and talk to a lawyer or HR about your options instead of gambling on a cleanse.
When to get a real answer
If this involves a medical procedure, probation, or a job offer, ask the testing lab which assay and cutoff they use. That tells you more than any chart online. This is general information, not medical or legal advice.