"Any threshold discussion should address the question if the DRUID approach to determine risk threshold as equivalents to 0.5g/L alcohol is feasible. From a scientific point of view it can only be justified to accept the same risk for all psychoactive substances (including alcohol). From a political point of view the determination of risk thresholds as equivalents to 0.5g/L alcohol might be questionable, because a BAC of 0.5g/L is not a legal limit in all European countries. Some Member States have lower alcohol limits and therefore risk threshold calculations for THC would have to be adapted accordingly. Besides, in European countries in which presently a certain risk is accepted, a discussion continues concerning alcohol zero tolerance approach."
Schulze, Horst, et al., "DRUID (Driving under the Influence of Drugs, Alcohol and Medicines) Final Report: Work performed, main results and recommendations," Project Funded by the European Commission under the Transport RTD Programme of the 6th Framework Program, Project No: TREN-05-FP6TR-S07.61320-518404-DRUID (Federal Highway Research Institute, Germany, Aug. 1, 2012), p. 84.