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Driving Under the Influence of Drugs: An Increasing Problem

J. Mørland, K-M. Beylich, A. Bjørneboe, A. S. Christophersen

National Institute of Forensic Toxicology, P.O. Box 9934, Ila 0132, Oslo, Norway


The Norwegian road traffic act prohibits driving under the influence of alcohol (A) and/or other psychoactive drugs (PD). In practice police officers refer the suspected driver to blood sampling without or with a clinical examination depending on suspicion of A or PD involvement, respectively. All blood samples are analyzed at one national institute. In PD cases written expert witness statements are accompanying the result of the clinical examination and blood concentration determinations, which together give the basis for sentences by the courts in a large percentage of the positive cases.

A dramatic change has been observed over the last 10 years with respect to A- and PD-cases. A-cases have declined from about 10 500 in 1983 to 5 500 in 1993, while PD-cases have increased from 800 to 3000 during the same period.

In 1993 52% of the A-cases had BACs between 0,05 and 0,15 per cent, and 41% higher than 0,15 per cent. 63% of the PD-cases contained PD, most often THC, amphetamine and benzodiazepines, the latter often in combination with other drugs or in high concentrations, 26% had BACs between 0,05 and 0,15 per cent, and 17% higher than 0,15 per cent. Additional analyses for PD in all A-samples during two months revealed such drugs in approximately 15% of the cases. Combination of our data gave the total picture in the whole national sample of drivers apprehended under the suspicion of drunken or drugged driving: A only (above 0,05 per cent) 51%, PD only 18%, A+PD 14% and 18% contained neither A nor PD. PD were present in 39% of cases with positive analytical results. This study appears to be the first conducted on a total national material focusing on PD and revealed a high prevalence of drugged driving.


The Norwegian road traffic act prohibits driving under the influence of alcohol and/or other psychoactive drugs. Per year approximately 8000 - 9000 drivers are apprehended by the police on the suspicion of either drunk or drugged driving. In all these cases a blood sample is taken shortly after the apprehension, and this sample is subsequently analyzed by a single national institute. The analysis for foreign substances is directed by the request from the police. The samples are routinely stored for more than one year. They can therefore be screened for other drugs than originally asked for retrospectively, in a systematic manner. This was done in the present study with all samples arriving during two months of 1993. The aim of this study was to find the prevalence of alcohol and/or other drugs in drivers as a group being suspected for influenced driving regardless of the primary suspicion of the cause of their influence.



The material consisted of the routine samples (10-20 ml whole blood in Therumo venoject tubes) sent to the National Institute of Forensic Toxicology (NIFT) from roadside traffic cases in the months February and September 1993. These were ordinary samples taken on the request by the police on the suspicion of influenced driving. The reason for the suspicion was seldomly given in the police documents, but was from other studies known to be strange, reckless, dangerous driving or involvement in accidents in the majority of cases. In total the institute received 1197 blood samples from drivers suspected of driving under the influence during these two months. In 739 cases the primary suspicion was influence of alcohol, in 458 cases drugs were suspected as the sole or additional cause of influence. When the analytical work required by the police was finished, all samples were analyzed for the substances indicated below (analytical). This was performed by noting the results obtained for those analyses already being performed for the police, anonymizing the samples, coding the results and then subjecting the samples to analysis for the rest of the foreign substances included in this study.


All blood samples were analyzed for alcohol (ethanol) by gaschromatography (GC) and an enzymatic (ADH) method, and screened for the following drugs: benzodiazepines, barbiturates, amphetamines, cocaine, cannabinoids, opiates, other strong analgesics, tricyclic antidepressants, neuroleptics, antihistamines and central muscle relaxants on appropriate immunologic and gas chromatographic methods used by NIFT for routine work. Positive results were confirmed by GC/MS-, HPLC- or GC methods and the substances were quantified versus calibrator samples made from dilutions of the respective pure compounds in blood bank blood. The results were corrected for losses during analysis by use of appropriate internal standards.


The prevalence of positive alcohol and drug findings in the material is presented in Table 1. Samples with BACs of 0.05% (the lowest legal limit in Norway) or lower were considered as negative in this Table.

Table 1
Distribution of Findings of Alcohol and other Psychoactive Drugs in Samples from Drivers Suspected of Driving Under the Influence

  n % female (%) male(%) median age (years)
Total 1197 100 8 92 29
Alcohol (>0.05%) Only 658 55 7 93 28
Drugs only 196 16 9 91 29
Alcohol and drugs 166 14 5 95 31
Neither alcohol nor drugs 177 15 12 88 29

It is seen from Table 1 that alcohol was found in 69 per cent of the cases, while the corresponding percentage for psychoactive drugs was 30. The low percentage of women, specially in the group combining alcohol and drugs is notable. The latter group had accordingly the highest male percentage and also the highest median age.

In Table 2 the distribution of drug findings is presented by BAC level. It is seen that the highest fraction of drug detections was found in alcohol negative samples. It was also interesting to observe that a substantial percentage of samples with alcohol also contained drugs. This percentage decreased somewhat from 25 to 18, by increasing BAC.

Table 2
Distribution of Cases with Detection of Psychoactive Drugs

BAC (%) n (total) n (with drugs) drug positive (in%)
0 259 167 64
0.0-0.05 114 29 25
0.051-0.10 179 39 22
0.101-0.15 220 50 23
>0,15 425 77 18

The cases with positive drug findings are presented in more detail in Table 3. This Table presents the material divided in five main groups, according to whether benzodiazepines, THC, amphetamine, opiates or other drugs had been found, mentioned in falling order of frequency of detection. The Table should be read e.g. for benzodiazepines that these drugs were detected in 206 samples. In 19 of these 206 samples only one single benzodiazepine was found, in 103 cases alcohol was present besides benzodiazepine(s), in 23 cases more than one benzodiazepine was found, in 54 cases THC was found in addition to benzodiazepine(s) etc. It is seen from Table 3 that the sum of the detections of the 5 main groups (n=526) exceeds the sum of drug positive cases (n=362). This was because many cases contained more than one drug. The details of these drug-drug combinations can be read from the subgroups, "with---". For all five main groups finding of the main drug alone, was rather the exception than the rule. Amphetamine cases had the highest frequency of measuring the main drug only (25%). In all groups combinations of three different drugs were seen, most frequently in benzodiazepine and THC cases. The majority of cases in which only a single drug was found exhibited substantial drug concentrations. This indicated supratherapeutic doses of medicinal drugs and recent use of illegal drugs. Finally other medicinal drugs than benzodiazepines were seldomly found. The main contribution to "other drugs" was made by psychoactive central acting muscle relaxants and paracetamol ( acetaminophene). Only one case with a neuroleptic drug was seen, and no cases with antidepressants and antihistamines.

Table 3
Drug Detections in Samples Containing Psychoactive Drugs (N=362)

Main drug Benzodiazepines THC Amphetamine Opiates Other drugs
Total 206 147 81 58 34
Single main drug only 19 33 20 8 11
With BAC>0.05% 103 61 5 21 17
With (other) benzodiaz. 23 54 38 19 11
With THC 54 - 39 13 1
With amphetamine 38 39 - 5 1
With opiate 19 13 5 - 4
With other drug 11 1 1 4 -


This study shows that the main finding in blood samples from subjects being suspected for driving under the influence is alcohol, which was found above the legal limit in 69 per cent of the samples. More surprising was the detection of psychoactive drugs in 30 per cent of the samples from people suspected for influenced driving. Thus in 35 per cent of samples where any detection (alcohol, other drugs) was made some psychoactive drug other than alcohol was found. There are few published studies available for comparison. In other studies drugs have been found in 7 to 30 per cent of blood samples from fatally injured drivers as reported from some countries ( for references see Gjerde et al, 1993). For living drivers who have not been subject to some kind of selection after apprehension before blood analysis, there are few published data. In a comparable smaller material from Norway, similar findings, as in the present study, were reported (Christophersen et al, 1990). In a Danish study it was found that 5.5 per cent of drivers suspected for drunken driving only had diazepam/N-desmethyldiazepam in their blood samples (Worm et al, 1985). In another report it was found that every third driver suspected to drive influenced by alcohol had another drug in his urine (Holmgren et al, 1985). Drugs can, however, be detected in urine for much longer time periods than in blood, long after their influence of the central nervous system has disappeared. In the present study blood was the only matrix analyzed. Our results, therefore, indicate recent use before driving. The frequent detection of illicit drugs, alone or in combinations, and the finding of supratherapeutic concentrations of therapeutic drugs in our material was accompanied by almost lack of finding of therapeutic drugs in therapeutic concentrations. Thus drivers on therapeutic drug regimens seemed to be represented very seldomly in suspicious driving calling the attention from the police. On the other hand these results probably reflect that people who are drug abusers often drive, and then in a way that gives rise to reaction from the police. The high concentrations found as well as the frequent detection of combinations in the present study, indicated that influence of driving ability was likely in the majority of the cases with detection of psychoactive drugs.

Norway is a modern industrialized western European country with a mixture of urban/suburban and rural population in the ratio 2:3. The size of the country is large (approx. 325 000 km2) compared to the population (4.3 million). The number of vehicles is about 3 million. The drug problems are considered to be rather below than above the European mean. Our finding that a psychoactive drug other than alcohol is involved in every third case under suspicion of influenced driving in this country comes from a non-selected, nationwide material. It can therefore probably to some extent be considered to be representative for other nations also. Differences in the awareness by the police of this problem, different legislation and other factors may contribute to variations between countries with regard to the real prevalence of the problem as well as to its discovery. Some generalizations appear, however, to be possible to make. The focus on alcohol should not mislead us to forget other drugs that could be present very often in suspected influenced driving cases. Thus a negative or low breath-alcohol test should not be used as the only measure to free a person from further investigation in suspected driving cases. Accordingly, the look for better tests to discover influenced driving due to other drugs than alcohol should be intensified.


Christophersen, A.S., Gjerde H., Bjørneboe, A., Sakshaug, J. and Mørland, J. Screening for drug use among Norwegian drivers suspected of driving under influence of alcohol and drugs. Forensic Sci. Int., 45:5-14, 1990.

Gjerde, H., Beylich, K-M. and Mørland, J. Incidence of alcohol and drugs in fatally injured drivers in Norway. Accid. Anal. and Prev., 25:479-483, 1993.

Holmgren, P., Loch, E. and Schuberth, J. Drugs in motorists traveling Swedish roads: On the road detection of intoxicated drivers and screening for drugs in these offenders. Forensic Sci. Int., 27:57-65, 1985.

Worm, K., Christensen, H. and Steentoft, A. Diazepam in blood of Danish drivers: Occurrence as shown by gas-liquid chromatographic assay following radioreceptor screening. J. of Forensic Sci. Soc., 25:407-413, 1985.