A ruling by Finland’s Supreme Court means that motorists will likely not be charged for driving under the influence days after using cannabis.
The influence of cannabis on users dissipates after some hours, however its "fingerprints" remain in the body for even longer. The court ruling aims to recognise that compounds related to metabolising cannabis may remain in the body for days after using the drug, although the user's ability to drive may not be impaired.
In Finland using cannabis is still illegal and drivers are still likely to be charged for the offence if they get behind the wheel hours after indulging in its use.
Cannabis usage leaves a substance known as tetrahydrocannabinol or THC in the body, prompting the production of a metabolite, carboxytetrahydrocannabinol (THC-COOH, where a metabolite is a substance required for or produced from metabolism.
THC is a psychoactive substance, which intoxicates people, so detecting it in a driver’s bold always results in a charge for driving under the influence. In Finland, police generally also issue a DUI citation if they find the metabolite THC-COOH in the blood.
However there is a major difference between the compounds.
Depending on the dosage taken, THC is known to leave the body between six and eight hours after cannabis use. However metabolites like THC-COOH may show up in blood samples for days or weeks longer. It is the equivalent of a cannabis "fingerprint" that reveals use of the drug in the recent past.
Unlike THC, the metabolite THC-COOH does not have an intoxicating effect and therefore does not impair the ability to drive.