Frequent detection of benzodiazepines in drugged drivers in Norway

To describe the Norwegian system for handling suspected drugged driving cases according to an impairment-based law, with primary focus on benzodiazepines (BZDs), blood concentrations and combination with other psychoactive compounds.

Routines for handling suspected driving under the influence of drugs other than alcohol are described. These include primary police investigation, blood sampling, and clinical tests of impairment performed by a police physician, a standard analytical program covering the most relevant illegal drugs and medicines relevant to traffic safety (approximately 25 compounds), and expert witness statements prepared for the court. The drug use patterns, blood drug concentrations, and frequency of multi-drug use have been recorded, with primary focus on benzodiazepines (BZDs). Use of BZDs among apprehended drivers has been compared with patient prescriptions recorded for the same BZDs.

One or more drugs have been detected in approximately 80% of the cases received for analysis every year. BZDs have been the most prevalent drugs and have been detected in 38-57% of the cases, which is more frequent than other common illegal drugs; e.g., tetrahydrocannabinol (THC; 30-43%) and amphetamine (33-39%). The majority of the BZDs have been detected at supratherapeutic blood concentrations and frequently in combination with illegal drugs, other psychoactive medicines, or alcohol. Less than 5% of the BZDs (except for nitrazepam - 7.6%) have been found to be the only drug present at therapeutic blood levels. The majority of the drivers were 20-39 years old (median age 29-33), while the majority of BZDs prescribed were to users over 50 years of age.

Drivers with BZD detected are probably not representative of ordinary patients with BZD prescriptions, as shown by the age disparity of drivers and patients. The frequent detection of BZDs suggests that these compounds should be included in the analytical program used for blood samples from apprehended drivers and for studies on drug involvement in road traffic accidents and risk calculations.