Explanation

THC (urine): what is measured?

The analysis looks in urine for breakdown products of THC, the main active substance in cannabis (weed and hash). THC itself disappears from the blood quickly, but the breakdown products are stored in fatty tissue and are then slowly released. This means cannabis use is visible in urine for much longer than its effect. The test does not measure whether someone is under the influence at this moment.

What can it detect?

Use of cannabis in the past days to weeks, by smoking, vaporizing or eating

Result

What does the result mean?

Positive result

A positive result means that there are breakdown products of THC in the urine above the limit the laboratory uses. According to the Trimbos Institute, cannabis is detectable in urine 5 to 30 days after use: most people test positive for about 5 days after one joint, and with daily use this can be longer than 30 days. The Dutch Society for Clinical Chemistry (NVKC) gives a detection time of more than a week for cannabis. A positive result therefore does not say when, how much or how often cannabis was used, nor whether someone was under the influence at the time of the test. A positive result shows that a substance is in the body; it is not a diagnosis and says nothing about dependence, the amount or the time of use.

Negative result

A negative result means that no breakdown products of THC were found above the laboratory's limit. This does not fully rule out use: shortly after use the result can still be negative, and with little or one-time use in diluted urine the value can stay below the limit. Drinking a lot lowers the concentration in the urine and can therefore give a negative result.

After an abnormal result

With a positive result that can have consequences, the laboratory has the result confirmed with a second analysis method. The GP then looks at the context: amount, frequency, symptoms and any wish to cut down or stop, and refers to addiction care if needed.

Reliability

How reliable is the test?

The test says something about use in the past days to weeks, not about health or the degree of use. The Dutch Society for Clinical Chemistry (NVKC) states that a positive result of a screening test must be confirmed with a second, different analysis method, because a positive result can have far-reaching consequences. The result is a snapshot of what is in the urine and not a judgment about someone's use or health. This text does not cover medical assessments or agreements with an employer; other rules and procedures apply to those.

What can affect the result?

A screening test can give a false-positive result; confirmation with a different method is needed before a result can carry much weight.
The detection time differs greatly from person to person and depends on how much, how often and in what way cannabis was used.
Fluid intake determines how concentrated the urine is; diluted urine can give a negative result.
The test measures breakdown products and not the effect: someone can test positive without being under the influence.

Who it is for

Who is the test useful for?

Useful for

Useful for a medical question from a treating doctor, for example in addiction care or with unexplained symptoms in which cannabis use may play a role. In people without such a question, the result adds little, because it says nothing about health or the amount used. If you are worried about your own use, help with cutting down or stopping is more useful than a test.

How common is it?

In 2025, 7.1 percent of adults in the Netherlands had used cannabis in the past year. Almost 1.5 percent used cannabis (almost) every day.

Trimbos Institute

Drawbacks and risks

A positive result can still occur long after the last use and can therefore give a wrong picture of recent use.
A result without a confirmation test can wrongly be used as evidence.

Get tested

THC (urine): test panels

THC (urine) is part of these test panels. You order online and have your blood drawn at a collection point or collect the sample at home.

Urine
THC
THC metabolites in urine as an indication of recent use.
€ 87,00

Evidence

Sources

This explanation is based on Dutch guidelines and independent information. It is general information, not a diagnosis. Discuss an abnormal result with your GP.

More about risks and results

More explanations

Other tests: Metals, toxins and medication

All tests