Blood draw · 3 analyses
Cannabis (THC)
Measures THC, 11-OH-THC and THC-COOH in your blood; shows whether and how recently cannabis was used.
€ 80,00
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Metals, toxins and medication · Blood
11-OH-THC
11-OH-THC, an active breakdown product of THC, in your blood; fits recent cannabis use and says the most together with THC.
At a glance
- Measured in blood
- In 1 test panel
- No special preparation
Explanation
11-OH-THC: what is measured?
When the body breaks down THC, the liver first makes 11-hydroxy-THC (11-OH-THC). This substance also has an effect itself, just like THC, and is then converted further into THC-COOH, which has no effect. After eating or drinking cannabis, THC first passes through the liver, so relatively much 11-OH-THC is formed; after smoking there is usually less 11-OH-THC than THC. The laboratory measures 11-OH-THC in serum with gas chromatography-mass spectrometry (GC-MS), together with THC and THC-COOH.
What can it detect?
- Cannabis use in the past hours to about a day
- Recent use of cannabis by eating or drinking, for example space cake
Result
What does the result mean?
11-OH-THC too high
A detectable amount of 11-OH-THC fits cannabis use shortly before the sample collection, just like THC itself. After eating cannabis, 11-OH-THC can be high compared with THC. According to Drugsinfo.nl, THC is sometimes detectable in blood for longer than 24 hours after eating cannabis; the same usually applies to 11-OH-THC, and with daily use it can also stay detectable longer. The level of the value is not a reliable measure of how strongly someone is or was under the influence, and says nothing about dependence.
11-OH-THC too low
A value below the laboratory's limit means that at the time of the sample collection there was no detectable amount of 11-OH-THC in your blood. This fits no use in the past hours to about a day. After smoking, 11-OH-THC is often lower than THC and can already be below the limit while THC is still detectable. Use from a few days earlier can usually only be seen in THC-COOH.
After an abnormal result
A detectable value does not need medical follow-up on its own. If you have doubts about your own use or want to cut down, you can discuss this with your GP or ask for anonymous advice at Drugsinfo.nl of the Trimbos Institute.
Reliability
How reliable is the test?
GC-MS is a specific and reliable measurement method. For 11-OH-THC on its own, there are no agreed limits or fixed meaning; the value mainly says something together with THC and THC-COOH, which the laboratory measures in the same blood. The result shows that cannabis was used shortly before the sample collection, but not exactly when, how much or how strongly someone was under the influence.
What can affect the result?
- 11-OH-THC falls quickly in the first hours after use; the time between last use and the sample collection largely determines the result.
- The ratio to THC depends on the way of use (smoking or eating) and differs from person to person.
- Medicinal cannabis, dronabinol and CBD products with too much THC also give 11-OH-THC.
- The laboratory measures in serum; those values cannot be compared one to one with measurements in whole blood.
Who it is for
Who is the test useful for?
Useful for
Useful as part of the test for cannabinoids in blood, together with THC and THC-COOH. As a value on its own, 11-OH-THC adds little. Not useful as evidence in a procedure, for a medical assessment or to establish whether someone can drive safely: separate tests with their own requirements and limits apply for that.
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, cannabis figures and trends 2025
Drawbacks and risks
- A detectable value can have unintended consequences if you share it, while it says nothing about fitness to drive at another moment or about dependence.
Get tested
11-OH-THC: test panels
11-OH-THC is part of these test panels. You order online and have your blood drawn at a collection point or collect the sample at home.
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.
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