How long is cannabis (THC) detectable?

No substance causes as much confusion about the detection window as cannabis. Someone who has taken a single puff is usually "clean" again within a few days, while a daily user can still test positive weeks later. That difference is no coincidence: THC is fat-soluble and accumulates in fat tissue, from which it is slowly released.

What a lab actually measures is not THC itself but the breakdown product THC-COOH. It stays detectable longer than the intoxicating effect, and that is exactly why a positive urine result is not the same as "under the influence now".

How long is cannabis detectable per matrix?

The times below are guide values for single use and for frequent use. With daily use, the urine window can rise sharply.

Why is the window for cannabis so variable?

Because THC is stored in fat tissue, the pattern of use matters more than for other substances. A high body-fat percentage, a slow metabolism and a high frequency all extend the window. In a daily user, THC-COOH is released from fat tissue day after day, so a urine test can still be positive weeks after the last use. In someone who used once, the substance drops below the cut-off within a few days. That same difference explains why two people who used on the same night can have a completely different result days later.

Drinking a lot of water does not help reliably: it dilutes the urine temporarily, but a certified lab recognises a diluted sample by the creatinine level and marks it invalid if necessary. Detox kits do not speed up breakdown either; only time does. The Trimbos Institute describes in the National Drug Monitor that cannabis is the most used illegal substance in the Netherlands, which explains why employers and the CBR often look for it when screening. The RIVM additionally records health incidents linked to use.

Which test fits which question?

The right test depends on what you want to know. If you want to check whether someone used recently, a saliva or blood test fits better, because those sit closer to current use. If it is about use in the past few days, urine is the logical choice. If you want to see a pattern over months, for example to distinguish occasional from structural use, a hair test is more suitable. A positive urine result therefore proves exposure within a window, not current impairment: with cannabis that distinction is larger than with almost any other substance.

What does a result mean?

For cannabis, a lab gives a quantified value of THC-COOH against a cut-off, not a single line. That matters, because a low value just above the cut-off can mean something different from a high value: the first fits declining use or passive exposure, the second more recent or heavier use. A rapid test does not make that distinction and only shows a line. Anyone who gets a result that has to mean something, for example with an employer or the CBR, therefore benefits from a lab confirmation. Passive smoke exposure rarely leads to a positive lab test at common cut-offs; the concentration usually stays below the threshold.

Can you test for cannabis at Zuivertest?

Cannabis is not part of our range. You can see which substances you can screen for specifically in our 10-panel. If you want to understand which panel fits your situation first, read 5-panel versus 10-panel. The broader view of all substances is in our overview of how long drugs stay detectable, and the other stimulants are covered in cocaine and MDMA.

Frequently asked questions

How long is cannabis detectable after smoking once?

After single use, THC-COOH is usually detectable in urine for 1 to 3 days. That is a guide value: a high dose or a slow metabolism can extend the window.

And with daily use?

Then the urine window can rise to about 30 days, because THC accumulates in fat tissue and is released slowly. In hair it stays visible for up to about 90 days.

Can passive smoke cause a positive result?

At common cut-offs, passive smoke exposure rarely leads to a positive lab test; the concentration usually stays below the threshold.

The windows above are guide values, not a guarantee, and vary per person. For questions about your health or about substance use, consult your GP; the WHO points to the health risks of frequent cannabis use.