The effects of cannabis wear off after a few hours. The traces remain much longer, because THC and its breakdown products are fat-soluble and are stored in fatty tissue. The body only releases them slowly from there.
In urine, tests look for the breakdown product THC carboxylic acid:
- after a single use, about three days,
- with daily use, ten to 15 days,
- with heavy long-term use, even more than 30 days.
In blood, THC itself can be detected for a few hours after a single use, and for longer with frequent use. Blood is what counts for the limit in road traffic.
Exactly how long depends on the amount, frequency, metabolism and the test method. The values vary widely. A urine test can therefore be positive even though the last use was weeks ago. This can have legal consequences, for example at a traffic check. Anyone who loses weight and burns body fat in the process releases stored breakdown products and may, in some cases, still test positive months later.
Remember: No longer high does not mean no longer detectable.
More on this: Road traffic and the law · Travel and work
Sources
- DGUV: Cannabis bei der Arbeit
- drugcom.de (BIÖG): Wie lange kann Cannabis nachgewiesen werden?
- Moeller, Lee, Kissack (2008): Urine Drug Screening: Practical Guide for Clinicians. Mayo Clinic Proceedings 83(1)
- Moeller et al. (2017): Clinical Interpretation of Urine Drug Tests, Mayo Clinic Proceedings 92(5), table of detection times