A Study of the Effects of Certain Tranquilizers and Small Amounts of Alcohol on Driving Performance


STUDY: Clayton, A.B., T.A. Betts, and G.M. Mackay. A Study of the Effects of Certain Tranquilizers and Small Amounts of Alcohol on Driving Performance. European J. Toxicol., 5:254-257. 1972.

Site: Departments of Transportation, Environmental Planning, and Psychiatry, University of Birmingham, United Kingdom.

Subjects: The 50 males and 50 females were mostly students, the mean age being 28.1 years. Their driving experience varied, and none normally took prescribed psychotropic medications.

Method: Subjects performed closed-course driving-tests under controlled conditions. They were generally tested in groups of six, using a fixed routine.

On Wednesday afternoon, subjects practiced for 1 hour on all driving tests at the driving site. They then received two unmarked bottles – one containg five drug tablets, the other five placebo tablets – along with directions of how and when to take them. (Both bottles used by the control group contained placebos.) One bottle was to be used first – one tablet Friday evening; three on Saturday (at intervals); and the fifth Sunday morning. Random double-blind administration techniques were used. On Sunday morning, subjects performed three runs on test 1, three runs on test 2, and five runs on test 3 (all described below). They received an objective assessment rating and answered a subjective questionnaire derived from Reisby and Theilgaard. After this they were given ethanol (0.5 g/kg) in flavored sugar base, to be drunk within 10 minutes. One hour later, the BAC was determined with a Breathalyzer and the testing procedures were repeated.

The following Wednesday, another practice session was held. From Friday to Sunday, subjects took the drugs in the second bottle, whereupon the testing cycle was repeated. Methods of scoring were accurately described.

Subjects drove a Ford ‘Escort Saloon,’ 2.98 meters long, Test 1 involved driving the vehicle around posts 5.97 meters apart in a straight line and then reversing back around the posts to the starting point. Test 2 required parking between two boards 5.97 meters apart and getting as close to the curb as possible, Test 3 measured gap estimation. Subjects were required to estimate a minimum distance between sets of posts through which they could drive and then to drive through the chosen gap.

Dosage: The drugs were administered in amounts approximately equal to the usual clinical doses: chlordiazepoxide, a benzodiazepine, 10 mg; amobarbital, a barbiturate, 30 mg; trifluoperazine, a phenothiazine, 2 mg; haloperidol, a butyrophenone, 0.5 mg; and alcohol, when given, 0.5 g/kg.

Results: Except for haloperidol, the drugs did affect driving performance. An analysis of results was done using a split-plot analysis of variance for each drug group for male and female subjects separately. Little evidence of alcohol-drug interaction was obtained, probably because of the low concentration of alcohol and chronic administration of drugs.

Some differences between men and women were found in tests in which skills were affected. The impairments were statistically significant, but were not detected by the subject or by objective clinical assessment. Physicians are advised to warn patients of these driving dangers, especially during early stages of medication.

Comment: This report is hard to follow, but its design seems acceptible. Insufficient information on statistical data analysis is supplied. Essentially, we are left with the statement that the ratio of significant results to nonsignificant results exceeded 1:20, and that all drugs (even haloperidol) showed at least one significant effect.

The work would have been much more useful if further data with much higher alcohol concentrations had been obtained.


Selections from the book: “Drugs and Driving”. Robert Willette, Ph.D., editor. State-of-the art review of current research on the effects of different drugs on performance impairment, particularly on driving. National Institute on Drug Abuse Research Monograph 11. March 1977.