Norway introduced legislative limits for driving under the influence of drugs (DUID) February 1st, 2012, to harmonize with the legislation on driving under the influence of alcohol. Per se limits corresponding to blood alcohol concentrations (BACs) of 0.02% were established for 20 drugs and concentration limits for graded sanctions corresponding to BACs of 0.05% and 0.12% were established for 13 of these drugs as well. The new system is not applied to individuals with valid prescriptions for medicinal drugs. The aim of this study was to investigate if the implementation of legislative limits for drugs affected the number of blood samples taken from suspected drugged drivers, drug findings and the number of expert witness statement requests. The number of blood samples taken in suspected DUID cases increased by 20% after introduction of legislative limits (3320 cases in 2010 and 3970 in 2013). The number of samples with at least one drug above the per se limit corresponding to BAC of 0.02% increased by 17% (from 2646 in 2010 to 3090 in 2013), whereas the number of expert witness statements was reduced by the half (from 63.4% in 2010 and 28.7% in 2013).