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Drug Usage by Persons Suspected of Driving Under the Influence of a Drug

J. Perl*, D.J. Mascord**, A.F. Moynham* and G.A. Starmer**

* Clinical Forensic Medicine Unit, Level 4, Sydney Police Centre, 151 Goulburn Street, Surry Hills, NSW, 2010, Australia

** Department of Pharmacology, University of Sydney, 2006, Australia


Random breath testing in New South Wales has had a successful impact on alcohol-related road trauma. While the precise extent of drug-impaired driving on traffic safety has not been established there is a perceived problem based on the extent of drug usage in drivers and on the demonstrable impairment of skills performance by drugs with the central nervous system activity.

This perception of drug involvement in traffic safety prompted the New South Wales Government to amend legislation to enable the taking of blood and urine samples from drivers suspected of being drug impaired.

This paper will present the procedures adopted in the taking of blood samples, the incidence of various drugs in apprehended and accident-involved drivers, a description of the population of suspected drug-impaired drivers and the reason for coming to police notice.

Results are presented for the period since the implementation of the legislation in 1987 and up to 1993. The impact of various procedural changes during that period will be discussed.


Driving under the influence of a drug (DUID) has been an offence in New South Wales for decades. Proof of the charge, however, depended on two criteria; the admission of the driver/rider and the observations of his/her behaviour by the Police Officer. If no admission of drug use was made, Police were obliged to release the driver, despite obvious signs of impairment. Under such circumstances, difficulties faced by Police in proving the DUID charge made the relevant section of the Motor Traffic Act virtually ineffective. An amendment to the Motor Traffic Act came into force on 1 December, 1987 which required blood and urine samples to be taken from drivers who were suspected by Police of being affected by a drug. This paper presents the findings of a preliminary analysis of DUID (n = 200) offences which occurred between January and December, 1992. The variables examined included age and sex of the driver, time and day of the week of offence, vehicle type, reason for coming to Police notice, drug admissions and blood analysis results.


Initially, the procedure required Police to witness the manner of driving or the way in which the driver was occupying the driving seat and attempting to put the vehicle in motion. The driver was then subjected to a breath test for alcohol and an assessment of the driver's demeanour was made. Urine and blood samples could only be taken if the breath test indicated that the driver was below the legal blood alcohol limit (0.05 g/100 ml). In N.S.W., there is no formal assessment procedure, such as Field Sobriety Testing or a Drug Recognition Experts Programme, as used in the U.S.A. Assessment is at the discretion of the Police Officer although a guide card of symptoms is provided to assist him/her. Once the driver/rider has been assessed and the Police Officer is of reasonable belief that the he/she is under the influence of a drug, he/she can be arrested and taken to hospital to provide blood (10 ml) and urine (100 ml) samples. The samples, taken by a Medical Practitioner or a Registered Nurse, are divided into two aliquots; one is given to the driver for private analysis and the other to Police. The samples must be obtained within two hours of the event which led to an assessment of insobriety. It is an offence to refuse to undergo an assessment, to refuse or fail to provide a sample of blood or urine, or both. Once the samples have been provided, the driver is free to go, but is advised not to drive. The samples are analysed by the Department of Health (Division of Analytical Laboratories). Urine is used for an initial screen and quantitative analysis is carried out on the blood sample.

A report by arresting Police concerning the circumstances leading to arrest and the results of the sobriety assessment must be submitted to the Police Pharmacologist. If no drugs are found, Police advise the driver of the result. If a drug is found, a report is prepared by a Pharmacologist, giving an expert opinion as to the likelihood of driving impairment being due to the drug(s) found. This report is based both on the blood analysis result and the Police observations.

Because the manner of driving had to be witnessed by Police, many accident-involved drivers were not subjected to blood/urine sampling. In 1989, the procedure was amended to include accident-involved drivers, where Police had reasonable belief that the person was under the influence of a drug. A further amendment to the Motor Traffic Act in 1990 allowed for the drug testing of blood samples taken from injured drivers who had been taken to hospital and who had not been breath analysed or subjected to sobriety assessment. These blood samples are routinely taken for alcohol analysis, but for a sample to also be tested for drugs, Police must have justifiable grounds to suspect that, at the time of the accident, the driver/rider was under the influence of a drug other than alcohol.

Initially, samples were only screened for a small range of drugs, including alcohol, cannabis, opioids, cocaine, amphetamines, barbiturates and benzodiazepines. It was found, however, that some drugs which are abused were not covered by the definition of "drug" in the Motor Traffic Act and, as changing patterns of drug misuse have been identified, the number of drug types in the screen has been increased.

Since 1987, the number of drivers found to have drug(s), other than alcohol, in their blood has steadily increased whereas the number of drug-negative results decreased initially and has remained reasonably constant since 1991 (Table 1).

Table 1
Drug-Positive and Drug-Negative Samples Received During 1987 - 1993 under Section 5A of the Motor Traffic Act

  Dec. 1987-
Dec. 1988
1989 1990 1991 1992 1993
Drug Positive 75 (58%) 151 (77%) 235 (90%) 284 (74%) 340 (84%) 352 (81%)
Drug Negative 55 (42%) 44 (23%) 25 (10%) 99 (26%) 67 (16%) 81 (19%)
Total 130 195 260 383 407 433


The sample cases were taken between January and December, 1992. The majority of the drivers in this sample population were male (83%). The age of the driver was not known in 46% of cases but of the remaining 54%, most were between 20 and 40 years old (43.5% of the total).

The majority (81%) of drivers came to notice between Tuesday and Friday; 35% came to notice between 7 pm and midnight and 54.5% between 7 pm and 6 am. Sedan drivers accounted for 85% of the sample, heavy vehicle (truck) drivers for 10% and motorcyclists for 2%. Of the 200 cases, 71 (35.5%) came to notice as a result of a collision and 111 (55.5%) for their manner of driving.

Drug use was admitted by 48% of drivers, with 23% admitting usage within 3 hours of coming to notice. Blood samples were obtained within two hours in 170 (85%) cases.

The sample population was examined in relation to admitted drug usage and the drugs which were detected in blood. Table 2 shows the major drug categories, admissions and drugs detected. Illicit drugs or therapeutic drugs which are commonly available illegally (e.g. benzodiazepines, ephedrine) were reported less frequently than detected in blood.

Table 2
Major Drug Categories, Admissions and Drugs Detected

Drug Category Admissions Found
b-adrenoceptor antagonists 0 0
cocaine 2 6
amphetamine 14 34
cough/cold preparations 0 0
anorexics 4 5
ephedrine 7 15
caffeine 1 0
hypnotics 10 12
anticonvulsants 4 4
minor tranquillisers 28 51
heroin 16 43
methadone 18 24
other narcotic analgesics 11 15
NSAIDs 2 1
aspirin/paracetamol 1 0
antihistamines 3 2
antidepressants 8 6
cannabis 80 159
other 2 4
alcohol 6 17
pseudoephedrine 0 19
Total 217 417

Table 3 shows the drugs detected and the means and ranges of the blood concentrations. Of particular interest are the drugs which are likely to be abused (e.g. heroin [detected as morphine], benzodiazepines, ephedrine, pseudoephedrine and amphetamines), which were frequently detected at toxic levels. Ephedrine and pseudoephedrine were most frequently detected in heavy vehicle drivers, who are known to abuse stimulants.

Table 3
Drugs Detected

Drugs found in blood (occurrences) Mean (range) in mg/L
phentermine (5) 0.12 (0.01 - 0.20)
codeine (27) 0.10 (0.01 - 0.64)
methadone (3) 0.20 (0.09 - 0.35)
morphine (43) 0.30 (0.02 - 1.96)
pethidine (1) 0.32
carbamazepine (1) 6.60
diazepam (19) 0.37 (0.05 - 1.10)
flunitrazepam (11) 0.05 (0.01 - 0.09)
nordiazepam (16) 0.49 (0.02 - 3.60)
oxazepam (17) 2.76 (0.10 - 20.0)
pentobarbitone (1) 1.00
temazepam (6) 0.83 (0.12 - 2.30)
bromazepam (1) 0.63
amphetamine (15) 0.22 (0.01 - 1.60)
dothiepin (1) detected
methamphetamine (19) 0.12 (0.01 - 0.74)
trimipramine (1) 0.12
ephedrine (12) 0.13 (0.01 - 0.78)
mepyramine (1) 0.25
pseudoephedrine (19) 0.34 (0.02 - 2.67) * 1 result of 88.0 mg/L
chlorpheniramine (1) 0.01
promethazine (1) 0.03
tetrahydrocannabinol (34) 0.007 (0.001 - 0.023)
D9-tetrahydrocannabinol acid (116) 0.034 (0.003 - 0.230)
cocaine (1) 0.01
benzoylecgonine (5) 0.09 (0.01 - 0.34)
alcohol (17) 0.116 g/100 ml (0.035 - 0.257)

Where only one drug was detected, it was classified as a stimulant or a depressant. If more than one drug was found, reference was made to the concentrations of the drugs so that a categorisation could be made about the likely net effect of the drugs. Cases involving D9-tetrahydrocannabinol acid alone were removed from the statistical analysis. This yielded 40 stimulant cases and 112 depressant cases. Statistical analysis of net stimulant/depressant effect versus the other variables was conducted on these cases.

No significant relationships were detected for day of offence, time of day or age. In those who had used depressants, speech was significantly more likely to be incoherent, slow and slurred whereas stimulant users were more likely to be talkative and to speak rapidly (C2 =16.19, d.f. = 7, p < 0.05). Stimulant users were significantly likely to have a runny nose and a dry mouth (licking lips), while depressant users were more likely to exhibit loss of control, to faint, to become unconscious or to have vomited (C2 = 25.95, d.f. = 6; p < 0.001).

Female motorists were significantly less likely to use stimulants than males (C2 = 4.13, d.f. = 1; p < 0.05). Stimulants were more likely to be used by heavy vehicle drivers (n=16, 100%) whereas depressants were more likely to be used by sedan drivers (n=109, 71.7%). This relationship was highly significant (C2 = 50.56, d.f. = 2; p < 0.001).

Examination of the signs and symptoms of intoxication which were reported by Police Officers, indicated that drivers using central nervous system depressant drugs were often noted to have glazed and bloodshot eyes, speech was slurred and slow or incoherent, the individual was unsteady, poorly coordinatied and apparently sedated. Cannabis users displayed similar symptoms to users of other CNS depressants, but enlarged pupils were also noted and the person often appeared to be dreamy or "distant". Some heroin users were found in an unconscious state and responded to the narcotic antagonist, naloxone. In addition to a general appearance of being under the influence of a CNS depressant, heroin users also often appeared to be disorientated and breathing was slow and shallow.

Ephedrine users were frequently noted to be restless, talkative and excitable. Although amphetamine users often displayed similar signs of stimulation, in the reactive depressive phase they were often unsteady, slow/sluggish in their movements and sedated.


While there are some significant drug/symptom associations indicated by these pilot sample data, it must be stressed that the sample size is small and there are a large number of variables. The entire case set (1988-1993) is being analysed and clearer relationships between individual drug categories and the other variables are expected to emerge. Cannabis was by far the most frequently detected single drug in drivers suspected of DUID, although other illicit drugs were more frequently detected than therapeutic drugs in this population of drivers.

It is clear from these data that the high proportion of drivers who were found to be drug-positive vindicates the procedure adopted in N.S.W. and it is also apparent that the number of drivers who were unnecessarily subjected to blood/urine analysis was small. The limited nature of the drug screen points to conservative findings for drug usage by these drivers.

It should be noted that the DUID legislation in N.S.W. does not aim to discourage drivers from legitimate drug therapy but attempts to improve road safety by removing drug-impaired (and frequently drug-abusing) drivers from the roads.