How long does THC remain in the blood, urine, and saliva?

17. 06. 2025

Briefly about THC
Methods for the detection of THC
Detection time: what influences how long THC stays in the blood?
Europe and driving under the influence of THC: Strict rules across the board
Conclusion
FAQ

Briefly about THC

Tetrahydrocannabinol (THC, delta-9 THC), the main psychoactive component of cannabis, affects the brain via CB1 receptors in the endocannabinoid system, causing changes in perception, relaxation, euphoria or increased appetite.

However, it also affects the ability to concentrate and motor skills, which is similar to alcohol. THC can adversely affect the ability to drive vehicles or operate machinery and greatly increases the risk of accidents when intoxicated.

In the body, THC is broken down mainly in the liver, where it is converted into inactive metabolites, mainly THC-COOH (11-nor-9-carboxy-THC), which are then excreted in the urine and faeces. As THC is highly fat-soluble, it can be stored with its metabolites in adipose tissue and released into the circulation gradually.

This means that the presence of THC can be detectable long after the effects have worn off, especially in regular users.

Infographic showing that THC is metabolised in the liver to inactive metabolites, primarily THC-COOH (11-nor-9-carboxy-THC)

Methods for the detection of THC

The presence of THC or metabolites can be detected by several methods. Each test not only has a different detection window, but also distinguishes different forms of THC, from active THC in blood to inactive metabolites in urine, and differs in sensitivity, accuracy and purpose of use. Some tests serve as quick reference checks, others have forensic or medical applications 👇.

Method of measurement	When they are used	What they detect	Detection time
Blood tests	To determine current intoxication Results have the highest evidentiary value in legal proceedings	Active THC circulating in the blood - demonstrates recent consumption and measures the exact THC level in ng/ml	For single use, THC is detectable for up to 24 hours For regular users a few days
Saliva tests	At roadside checks Screening method (orientation test) A positive result is used as a basis for further testing (blood test)	THC in oral cavity and saliva - evidence of recent consumption	6-24 hours after use For high dose or sensitive tests up to 30 hours
Sweat tests	At the roadside check Less common method	The patch traps metabolites in sweat	Metabolites may take days to weeks to be detected
Urine tests	During withdrawal or anti-doping checks In occupational medicine practice	Major metabolite 11-nor-9-carboxy-THC (THC-COOH)	For single use, about 3-7 days For frequent users 1-4 weeks, rarely longer
Hair analysis	In forensic and forensic investigations When monitoring abstinence For jobs with high responsibility	Metabolites stored in the hair fibre	Metabolites can be detected several months in the future

Detection time: what influences how long THC stays in the blood?

Dose and frequency of use play a key role. While the effects of THC wear off within hours, it can still be detected in body fluids days or weeks later.

Several factors affect the detection time of THC in the blood:

Dose and frequency of use - The higher the dose and the more frequent the use, the longer THC remains detectable in the blood and other body fluids. Regular users keep THC in their bodies longer.
Method of consumption - oral forms (e.g. edibles) are absorbed more slowly, whereas vaping has an almost immediate onset of effects and also a faster absorption of THC into the bloodstream. This difference affects not only the duration of action but also how long and at what concentration THC can be detected in the body.
THC concentration in cannabis: Stronger cannabis varieties or concentrated forms may leave more metabolites and extend the detection window.
Metabolism and body composition - THC is stored in fat, and therefore degradation depends on body composition.
Hydration and physical activity - Dehydration can increase THC concentrations in the blood, as can physical activity, which can release THC from fat stores back into the circulation.
Test sensitivity - modern tests are very accurate, but each has a different detection limit, the so-called "cut-off".

Infographic showing factors affecting how long THC remains in the blood – including method of consumption (edibles, vaping), hydration, physical activity, metabolism and sensitivity of specific tests

Europe and driving under the influence of THC: Strict rules across the board

There is no uniform legislation on driving under the influence of THC within the European Union - each country sets its own rules 🌍. However, most countries choose a very restrictive approach.

Either zero tolerance or very low blood THC limits (typically between 0.3-3 ng/ml) are set. In practice, this means that even trace amounts of THC can be grounds for a penalty, whether in the form of a fine, a driving ban or even criminal proceedings under a particular country's legislation.

Conclusion

Different tests differ not only in the way they are performed, but also in how long after use they can detect THC. Blood tests mainly detect current or very recent use. Saliva and sweat tests detect use within hours to days. Urine THC tests can detect use over a longer time span - from days to weeks. And hair analysis can detect THC use going back several months.

How long THC stays in the body depends on a number of individual factors - the size of the dose and frequency of use are key.

Each organism reacts differently and therefore the detection time can vary significantly from case to case.

FAQ

1. How accurate are blood tests for THC?

THC blood tests are one of the most reliable methods for detecting the actual presence of THC in the blood and can measure the exact concentration of THC in the body in ng/ml. They detect active THC, not just metabolites, and are mainly used in traffic accidents, inspections or court proceedings.

Blood tests serve as a confirmatory method - for example, if a driver fails a saliva or sweat test, he or she must have a medical examination with a blood sample to accurately determine the THC level.

The result of a blood test is of the highest evidentiary value and in legal or administrative proceedings it is the toxicological analysis of the blood that is the decisive basis, not the orientation test.

2. How long does THC remain in the urine?

THC can be detected in the urine for a longer period of time than in the blood - from a few days to several weeks, depending on the frequency of use.

However, it is not the THC itself that is sought in the urine, but the main metabolite 11-nor-9-carboxy-THC (THC-COOH), which is produced in the liver and gradually excreted by the kidneys. This metabolite may be detectable in the urine for several days to weeks depending on the intensity of use - approximately 1 to 30 days after the last use.

However, a positive result does not demonstrate actual effects, as THC metabolites can persist in the urine long after the effects have worn off. For this reason, urine tests are not used to assess current intoxication.

3. When are saliva tests for THC used?

Saliva THC tests are mainly used at roadside checks as a quick "screening". They will detect recent use (usually within 24 hours) but are not as accurate as blood tests and are more of a first indication.

4. Can I drive after taking CBD?

CBD, or cannabidiol, is generally considered to be a safe substance suitable for everyday use. Unlike THC, it is not psychoactive and does not cause a state of intoxication.

Research from 2022 looked at simulated driving performance in 17 participants after taking a placebo and 3 different doses of CBD (15 mg, 300 mg and 1,500 mg). Results confirmed that none of these doses produced subjective or objective signs of intoxication, while not impairing driving or mental performance.

Another study in 2020 concluded that even very high doses of CBD (up to 1 500 mg) did not affect cognitive ability or driving performance.

However, the effects of CBD can be individual for each user.

Some people may experience sedation, which could affect driving reactions. It is therefore important that each driver first checks how CBD affects them and if they are unsure or experience any impairment, they should avoid driving.

4. Will any of the tests prove CBD consumption?

Conventional drug tests focus on detecting THC and its metabolites - CBD is usually not detected. Pure CBD should therefore not appear in these tests. However, it is important to know that some full-spectrum CBD products may contain trace amounts of THC (e.g. 0.2-0.3%), which can build up in the body and test positive when taken regularly or at high doses.

Therefore, drivers are advised to reach for broad-spectrum CBD products or isolates that are THC-free.

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Author: Patricie Mikolášová

Photo: AI

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