The effect of alcohol, THC and their combination on perceived effects, willingness to drive and performance of driving and non-driving tasks

Accid Anal Prev. 2010 Nov;42(6):1855-65. doi: 10.1016/j.aap.2010.05.006. Epub 2010 Jun 9.


Background: Driving under the influence of drugs (DUID) is one of the main causes of car accidents. Alcohol and marijuana are the most popular drugs among recreational users. Many classify these drugs as "Light" drugs and therefore allow themselves to drive after consuming them.

Objective: The study had two main objectives: 1) to investigate the effect of alcohol (BAC=0.05%), THC (13 mg) and their combination on driving and non-driving tasks. 2) to investigate the extent to which people are willing to drive based on their subjective sensations and their perceived effects of the drugs.

Method: 7 healthy men and 5 healthy women, ages 24-29, all recreational users of alcohol and marijuana, completed 5 experimental sessions. Sessions included: drinking and smoking placebo, drinking alcohol and smoking placebo, drinking placebo and smoking THC, drinking alcohol and smoking THC, drinking placebo and smoking placebo 24 hours after drinking alcohol and smoking THC. Three types of measures were used: subjective perceptions (with questionnaires), performance parameters of the driving and non-driving tasks (arithmetic task and a secondary target detection task) and physiological changes (heart rate).

Results: Overall, the combination of alcohol and THC had the most intense effect after intake. This effect was reflected in performance impairments observed in the driving and non-driving tasks, in the subjective sensations after intake, and in the physiological measures. Despite significant differences in the size of the effects after the various treatments, there were no differences in the distances subjects were willing to drive while under the influence on each of the treatments.

Publication types

  • Controlled Clinical Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Accidents, Traffic / prevention & control*
  • Accidents, Traffic / psychology*
  • Adult
  • Alcoholic Intoxication / psychology*
  • Arousal / drug effects
  • Attention / drug effects
  • Attitude*
  • Automobile Driving / psychology*
  • Dronabinol / adverse effects*
  • Drug Synergism
  • Ethanol / blood
  • Female
  • Health Knowledge, Attitudes, Practice
  • Humans
  • Male
  • Marijuana Smoking / adverse effects*
  • Marijuana Smoking / psychology*
  • Pain Measurement
  • Problem Solving / drug effects
  • Psychomotor Performance / drug effects*


  • Ethanol
  • Dronabinol