Can I drive stoned?

The last amendment came into force on January 1, 2005. The explanation of the amendment states under the item “1.5 Narcotic limits”:

“In principle, proof of incapacity to drive due to narcotic and drug use must be established by applying the three-pillar principle: Based on the police findings (first pillar), medical findings (second pillar) and the chemical-toxicological analysis results (third pillar), the inability to drive is determined by a forensic medical expert. The three-pillar principle can be deviated from if widespread substances are involved that are known to have a negative effect on driving ability. Then the detection of one of these substances in the blood is sufficient to prove the inability to drive (zero limit). For the time being, these substances are heroin, morphine, cocaine, various forms of amphetamines (designer drugs) and cannabis.”

The actual regulation then states that “tetrahydrocannabinol (cannabis)” when detected in the blood will result in inability to drive. If this is proven, it is a misdemeanor and will be punished accordingly, in addition to a temporary withdrawal of identification and then the procedure at the Road Traffic Office (see also here).

If the blood is now measured using modern methods, the level of psychoactive THC can be determined there: Nanograms per milliliter of blood plasma or micrograms per liter of blood plasma. (Similar with alcohol: in the blood one can determine the per mille content of alcohol). But what does the active ingredient content in the blood tell us? Can one conclude from these values whether a person is actually stoned or alcoholized? In the case of alcohol, the legislator says yes and means that more than 0.8 (until 2004) or 0.5 (from 2005) per mille is not permissible for driving a vehicle. And vice versa, this means that someone with 0.4 per mille of alcohol is allowed to drive a car. In the case of illegal drugs, however, the limit should be zero, or the limit of what the measuring device can just measure (about one nanogram per milliliter). Thus, with the regulation introduced at that time, simply the presence of a quantity of THC in the blood, however small, is sufficient for a determination of inability to drive. This has made it much easier to criminalize THC users.

So says Iten's standard work, “Driving Under the Influence of Drugs/Medications.”

“THC plasma concentrations of one microgram per liter and greater are suggestive of moderate cannabis use within the past four hours in occasional users. However, in heavy users, such concentrations may be observed up to two days after last use.”

Yet when someone is really stoned, they don't have a few micrograms in their blood, but 100s or even hundreds of micrograms.

Those who smoke pot occasionally should therefore not have smoked pot for six hours before driving. Regular smokers, on the other hand, are never fit to drive, unless they stop smoking for three days before driving. Here we see clearly that the zero limit goes far beyond the goal of removing only the unfit smokers from traffic. It makes driving impossible for regular THC users, even if they always put a night between using and driving!