"The following conclusions can be drawn:
"• It is advised to establish legal risk thresholds for illicit drugs on the basis of solid empirical data, i.e. experimental and epidemiological results. If the empirical basis is too weak, pharmacokinetic substance characteristics could help to define a lower effect limit.
"• The risk thresholds for drugs should reflect the impairment equal to that of 0.5g/L BAC or to any other legally relevant BAC.
"• The risk threshold for THC should be set adequate to 0.5 BAC at 3.8 ng/mL serum plus an added value for measurement error and confidence interval.
"• For all other illicit drugs a zero-tolerance should be implemented, as the empirical database does not allow a definition of risk thresholds yet. In order to determine the limit of effect, all information regarding the drug effects and its pharmacokinetics should be considered by national expert teams. Those teams could use the comprehensive data provided by DRUID. Thereby it could be avoided that further development of the analyzing methods leads to a constant decline of the limits of quantification."


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. 85.