Impairment based legislative limits for driving under the influence of non-alcohol drugs in Norway.
When non-alcohol drugs are detected in blood samples from apprehended drivers in Norway, individualised expert opinions are required to evaluate degree of impairment. For alcohol, legislative limits have been in use since 1936. To harmonize the current practice for driving under the influence of alcohol and non-alcohol drugs, a judicial reform with legislative limits for non-alcohol drugs has been suggested. Impairment limits, representing drug concentrations in blood likely to be accompanied by a degree of impairment comparable to a blood alcohol concentration (BAC) of 0.02%, were proposed for 20 psychotropic drugs, including the most prevalent benzodiazepines, cannabis, GHB, hallucinogens and opioids. Limits for graded sanctions, representing drug concentrations in blood likely to induce impairment comparable to BACs of 0.05% and 0.12%, were defined for 13 of the 20 substances. The suggested limits were based on assessments of impairment after single doses of the drugs in naïve individuals. The proposed limits will not apply to individuals with valid prescriptions for medicinal drugs, where the present system with individualised expert evaluations will be maintained. Norway is the first country planning to implement legislative limits for non-alcohol drugs corresponding to impairment seen at increasing BACs. The background and justification for the suggested limits are presented herein.