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Drugs and driving

USA [1]
Results
Australia [2]
Results
Holland [3]
Results
New Zealand [4]
Results
Comment

We know that people who drink alcohol and have blood alcohol concentrations above a certain level are much more likely to have a motor vehicle accident than those who have no alcohol present. It is why we have strict drink-driving regulations. But what about drugs, particularly the so-called recreational drugs? This is something of a moving target because patterns of recreational drug use change over time. A quick review of some recent studies from around the world tells that drugs and driving is at least as big a problem as alcohol and driving.

USA [1]


The setting was a cohort of traffic accident victims admitted during a six-month period to a trauma centre servicing most of Maryland, and for whom there was both a blood alcohol result and a sufficient urine specimen for drug analysis. Demographic variables were recorded, and toxicology results that could have resulted from medications administered during treatment were disregarded. Status (driver, passenger, pedestrian) was not available.

Results


Over the period there were 322 eligible patients, predominantly (71%) male, and about half were aged under 35 years. Overall 59% had a positive toxicology test, and drugs, with and without alcohol, were involved in almost three-quarters of the positive results (Figure 1).


Figure 1: Toxicology tests in RTA victims in Maryland






Blood alcohol levels were above the drink drive limit of 80 mg/dL in all but three of the positives, and the average alcohol concentration in those with alcohol present was 210 mg/dL. Alcohol was the commonest single drug present, with benzodiazepines and cannabinoids also present in over 15% (Figure 2). Positive tests were found less frequently in women than men, except for benzodiazepines.


Figure 2: Ranking of positive toxicology tests in Maryland






Australia [2]


Here the setting was 3,398 fatally injured drivers from three Australian states between 1990 and 1999. Only on-road crashes were included, and any considered to be suicide were excluded. Drivers were identified mainly from coroners' records and central toxicology laboratories. Analysis of each case analysed the degree of responsibility of each driver for the accident, an index of culpability divided into responsible for the crash, contributor, or not responsible.

Results


Most were car drivers (77%) or motorcyclists (19%). Most (about 80%) were men, and the average age was about 35 years, with a range of 12 to 92 years. Alcohol above 50 mg/dL in blood was found in 29%, drugs of any type 27%, and 10% of cases involved alcohol and drugs. The most commonly found drugs were cannabinoids (14%), opioids (5%), stimulants (4%) and benzodiazepines (4%).

Using those drivers who tested negative for alcohol or drugs as controls, drivers in the age range 30-60 years were less likely to be responsible for the accident. The ratio of drivers responsible to those not responsible was much higher (11) for positive cases than negative cases (3). High ratios were found for high blood alcohol (34), single vehicle crashes (27), drivers aged 17 years or below (12), and positive tests for cannabinoids (10) and psychoactive drugs (11) only.

Responsibility for accidents appeared to be concentration-related, at least for alcohol and cannabinoids. For alcohol (Figure 3), compared with those drivers without alcohol or drugs, the odds ratio for being responsible for the crash increased with blood alcohol concentration. Higher cannabinoid concentrations also raised the likelihood of driver responsibility.


Figure 3: Driver responsibility for crash, odds ratio by blood alcohol compared with no alcohol detected






Holland [3]


A different approach was taken for controls in Holland. Here cases were car or van drivers involved in road crashes and needing hospital treatment in 2000 and 2001, in a population of 350,000. Controls were drivers recruited at random while driving on public roads. As best as possible, controls were drivers matched for age and sex, and for time of day. There were 110 cases and 816 controls.

Results


Three quarters of the cases were men, with an average age of 39 years. Controls were generally similar in demographics. Alcohol or drug tests were positive in 40% of cases, compared with 14% of controls. Alcohol was commonest, followed by cannabis and benzodiazepines (Figure 4). Only the use of a single drug without alcohol had a similar incidence (9%) in both cases and controls. Compared with no drug, use of multiple drugs plus alcohol carried a 100-fold increased risk of road accident injury.


Figure 4: Positive toxicology tests in Dutch drivers in accidents involving injury, compared with randomly selected non-crash drivers






New Zealand [4]


Drivers involved in 571 car crashes involving death or hospital admission of at least one occupant were compared for cannabis use with 588 randomly selected drivers in and around Auckland, with a population of about 1.1 million, in 1998 and 1999.

Results


The average age of crash drivers was 37 years, and 59% were men. Drivers and controls were well matched. Blood alcohol concentrations above 50 mg/dL were found in 23% of crash drivers and 1% of controls. Cannabis use within the last three hours was admitted by 6% of drivers involved in crashes, and 10% admitted using cannabis once a week or more. The figures for controls were below 1%.

Comment


These four studies come from different parts of the world, at different times over the past decade or so. Yet they demonstrate remarkable consistency. Alcohol remains the major factor, but with cannabinoids and benzodiazepines not that for behind in most of the studies.

Where dose was examined, there was a significant dose response for alcohol and cannabinoids. In the large Australian study, cannabinoid concentrations ranged from less than 1 μg/L to a staggering 228 μg/L, with the median value of 9 μg/L. Concentrations above 5 μg/L have been particularly associated with responsibility for accidents. In the US study, mean alcohol concentrations were 2-4 times the legal limit. For both alcohol and cannabis, where it was present it was present in concentrations known to cause problems.

Cannabis was found consistently in accident victims or drivers. It is not an easy drug to understand, with problems with acute and habitual use. A comprehensive, if not overtly systematic, review [5] pulls together evidence from various sources for those wanting a more detailed appreciation. The bottom line from the review is that cannabis makes it more difficult to drive on simulators, is associated with car accidents, and that alcohol and cannabis combined is an explosive mix that produces severe impairment of cognitive, psychomotor, and actual driving performance.

On a technical note, these four studies each choose different populations for cases and controls. The cases can be drivers or any person involved in an accident; they can be dead or alive. Controls were those testing negative, or randomly chosen drivers. In the latter case, a significant minority refused to cooperate - with implications for how many people take drugs and drive. It could be substantially more than these surveys revealed.

References:



  1. JM Walsh et al. Epidemiology of alcohol and other drug use among motor vehicle crash victims admitted to a trauma center. Traffic Injury Prevention 2004 5: 254-260.
  2. OH Drummer et al. The involvement of drugs in drivers of motor vehicles killed in Australian road traffic crashes. Accident Analysis and Prevention 2004 36: 239-248.
  3. KL Movig et al. Psychoactive substance use and the risk of motor vehicle accident. Accident Analysis and Prevention 2004 36: 631-636.
  4. S Blows et al. Marijuana use and car crash injury. Addiction 2005 100: 605-611.
  5. JG Ramaekers et al. Dose related risk of motor vehicle crashes after cannabis use. Drug and Alcohol Dependence 2004 73: 109-119.

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