Why there is no single answer
The honest range for how long cannabis stays detectable is anywhere from a few hours to more than ninety days, and the reason the range is that wide is that four different tests are looking at four different things at four different levels of sensitivity.
Urine looks for metabolites. Blood looks for the active compound itself. Saliva looks for both. Hair traps metabolites as it grows. Each has its own window, and none of them measure impairment.
So the answer depends on which test, how often you use, how much you use, and what your body does with it. This is a breakdown by test type, with the variables that move the timeline.
Detection windows by test type
| Test | Occasional use | Heavy daily use |
|---|---|---|
| Urine | 3-10 days | 30-60+ days |
| Blood | 12-24 hours | 2-7 days |
| Saliva | 12-24 hours | 1-3 days |
| Hair | Up to 90 days | 90+ days |
These are typical ranges, not guarantees. Individual results vary substantially in both directions.
Urine: the one that matters for most people
Urine tests detect THC-COOH, a metabolite stored in body fat and eliminated slowly. This is why the window is so much longer than the drug’s actual effect, which lasts hours.
Single use: usually detectable for three to ten days. Weekly use: up to three weeks. Daily heavy use: thirty to sixty days, and in chronic long-term heavy users with high body fat, occasionally longer.
The standard screening threshold is 50 ng/mL, with a confirmation test at 15 ng/mL by GC-MS if a screen comes back positive. Some employers and programmes use lower cutoffs, which extend the window considerably.
Blood: short, and not about impairment
Blood tests measure active THC rather than metabolites, so they clear quickly — typically within twelve to twenty-four hours for occasional users, and a few days in heavy users.
An important caveat: a positive blood test indicates recent use, not impairment. Regular users can have detectable THC without being impaired, and occasional users can be impaired with low levels. This is the central problem with per se THC driving limits in law, and why several jurisdictions use roadside behavioural assessment plus an impairment threshold rather than a simple cutoff.
Saliva: short and increasingly common
Oral fluid testing is fast, non-invasive and used at roadside in several countries. Detection runs roughly twelve to twenty-four hours for occasional use and up to three days for regular use.
Saliva testing correlates somewhat better with recent use than urine, but it is easily affected by eating, drinking or smoking anything else in the preceding minutes, which is why protocols require a waiting period before sampling.
Hair: the longest window of all
Hair testing detects metabolites deposited in the follicle as hair grows, giving a look-back of roughly ninety days — the length of the hair sample. It is expensive and used less often in employment screening, but it is the most difficult to argue with because the timeline is fixed by growth.
Cosmetic treatments, bleaching and heavy shampooing can degrade or remove some detectable residue, which is why laboratories test for signs of tampering. This is not a reliable strategy.
What moves your personal timeline
Frequency and quantity
The dominant variable. Chronic daily use saturates fat stores, which then release metabolite slowly. Occasional use never builds that reservoir.
Body fat percentage
THC is fat-soluble. Higher body fat means a larger storage compartment and slower elimination. This is why two people with the same habit can have very different clearance times.
Metabolism and age
Faster metabolism generally means faster clearance, though the effect is smaller than frequency or body composition. Age slows metabolism broadly.
Hydration and exercise
Both influence urine concentration, which affects whether a sample crosses a threshold on a given day. They do not meaningfully accelerate elimination from fat stores.
The test’s cutoff
A 50 ng/mL screen and a 15 ng/mL confirmation are different tests with different windows. So are the stricter cutoffs used in some safety-sensitive roles.
What does not work, and what marginally helps
Be sceptical of anything sold as a detox kit. Most are diuretics and fibre, and their main effect is dilution — which is itself detected through creatinine and specific gravity checks, and which can be treated as a refusal or a tamper.
What genuinely helps: time, and reduced intake. Stopping earlier is the only intervention with reliable effect. Exercise increases metabolism and mobilises stored fat, which can temporarily raise metabolite levels before lowering them — which is why heavy exercise immediately before a test is counterproductive.
Masking agents, synthetic urine and substitution carry real consequences if detected, up to and including termination or legal action depending on context.
The test that is actually being run, and why it matters
Most workplace and pre-employment screening is a two-stage process. The first stage is an immunoassay screen, cheap and fast, which flags a sample as positive above a cutoff — commonly 50 ng/mL for THC metabolite.
Anything that flags goes to confirmation by gas chromatography-mass spectrometry, which identifies the specific compound at a much lower threshold, often 15 ng/mL.
This two-stage structure explains a common experience: a home test says negative, the lab says positive. The home test used a 50 ng/mL cutoff; the confirmation ran finer. It is not a mistake, it is a more sensitive test applied to the same sample.
It also means that knowing your cutoff is as important as knowing your habit. The same person can pass one programme and fail another without changing anything.
What the research says about impairment and driving
Detection windows are often confused with impairment, and it is worth being precise about the difference. Blood THC concentration correlates poorly with impairment, especially in regular users who develop tolerance to the behavioural effects while still testing positive.
Studies of crash risk consistently find an association between recent cannabis use and increased collision risk, but the mechanism is contested and the effect size varies widely between studies. What is not contested is that combining cannabis with alcohol produces a substantially greater impairment than either alone, well beyond what the arithmetic would suggest.
Practically: if you have used cannabis, do not drive. Not because a test will catch you, but because the window in which you are impaired and the window in which you are detectable are two different windows, and only one of them is about your safety.
Does the form of cannabis change anything?
Marginally. Edibles produce more of the potent 11-hydroxy-THC metabolite, which may extend detectability somewhat. Vaporised and smoked flower clear similarly. CBD products are a separate consideration: heavy use of full-spectrum CBD can produce a positive result, though far less reliably than THC products.
For the THCa-specific version of this question, see how long THCa stays in your system.
Frequently Asked Questions
How long does weed stay in your system?
It depends on the test. Urine detects occasional use for 3-10 days and heavy daily use for 30-60 days. Blood and saliva clear within one to three days. Hair retains metabolites for roughly 90 days.
Does drinking water flush THC out?
No. Water dilutes urine, which can lower the concentration on a given sample, but laboratories check creatinine and specific gravity specifically to detect dilution. It does not accelerate elimination from fat stores.
How long does weed stay in urine for a casual user?
Typically three to ten days after a single use. Weekly users often clear within two to three weeks. The dominant variables are frequency, quantity and body fat percentage.
Can a blood test show how high I am?
Not reliably. Blood THC indicates recent use rather than impairment, and the correlation between concentration and impairment is weak, particularly in regular users who develop tolerance.
Does CBD show up as THC on a drug test?
Usually not, but it can. Full-spectrum CBD contains trace THC, and heavy use can accumulate enough metabolite to trigger a screen. CBD isolate carries essentially no risk.