Combined Alcohol and Cannabis Effects on Skills of Young Drivers

July 23, 2026 updated by: Christine Wickens, Centre for Addiction and Mental Health

Effects of Combined Alcohol and Cannabis on Young Drivers' Simulated Driving

Alcohol and cannabis are the two most widely used substances of abuse in the world and are the psychoactive substances most often found in seriously and fatally injured drivers. In a recent study, it was observed that individuals who reported both driving under the influence of alcohol (DUIA) and the influence of cannabis (DUIC) experienced collision risk that was nearly 4 times that of individuals who reported driving after using only one of these drugs. Recent research in the United States and Canada indicates that the prevalence of DUIC among young drivers of high school and university age, and young adults is similar to, or higher than, the prevalence of DUIA. This is a serious public health issue, since motor vehicle collisions are the leading cause of death in this age group. Given the frequency with which alcohol and cannabis are consumed together, it is important to understand their combined effects on driver behaviour. The current study will examine the acute effects of a moderate dose of cannabis (12.5% THC) combined with an intoxicating amount of alcohol (BAC=0.08) on driving simulator performance of young drivers. Following an eligibility screening and practice session, a total of 70 participants aged 19 to 29 years will each complete 4 experimental sessions. During each session, participants will drink alcohol or placebo alcohol and smoke an active or placebo cannabis cigarette. The effects of alcohol and cannabis on the performance of driving-related skills will be assessed using a high-fidelity driving simulator. Cognitive, psychomotor, and mood effects will also be assessed.

Study Overview

Status

Completed

Conditions

Intervention / Treatment

Detailed Description

The proposed study will pursue the following primary aims:

Aim 1: Examine the acute effects of a moderate dose of cannabis (12.5% THC) combined with an intoxicating amount of alcohol (BAC=0.08) on driving simulator performance of young drivers. Simulated driving performance, tests of cognition, verbal memory, and mood will be measured concurrently with BAC and levels of cannabinoids in biological fluids before and after acute drug exposure in male and female drivers aged 19 to 29. BAC and biological fluids will be measured up to 5 hours following drug exposure.

Aim 2: Explore the effects of driving history, driving attitudes, and individual difference measures (e.g., demographics, drug and alcohol use, etc.) on the acute effects of alcohol and cannabis on driving simulator performance of young drivers. Exploratory analyses will be undertaken to determine if the acute effects of cannabis plus alcohol on the driving simulator task are influenced by these measures.

Study Design and Duration

This study will be a within-subjects, double-blind, double-dummy, placebo-controlled, counterbalanced, randomized clinical trial assessing the impact of alcohol and cannabis combined on driver behaviour. Although a placebo condition is part of the study, this is not a treatment study.

Initial contact with potential participants will be made via telephone, and study personnel will conduct a telephone screen for eligibility. Upon eligibility confirmation by telephone, participants will be asked to attend CAMH for an eligibility assessment. Participants will attend CAMH for a total of 6 study sessions (an eligibility assessment, a practice day, and 4 test sessions).

At each of four test sessions, participants will undergo one of these alcohol and cannabis exposure conditions: 1) placebo alcohol and placebo cannabis; 2) intoxicating dose of alcohol and placebo cannabis; 3) placebo alcohol and active cannabis, and; 4) intoxicating dose of alcohol and active cannabis. The order of these conditions will be randomly assigned. Participants will complete the alcohol manipulation followed by the cannabis manipulation. The alcohol and cannabis exposure sessions will be separated by at least 72 hours.

Participants will be asked not to use cannabis for 72 hours and alcohol for 48 hours prior to attending CAMH.

In certain instances, the Qualified Investigator may ask a participant to return for re-screening, e.g. repeat of urine test or other assessments performed for eligibility assessment. Also, in case of unforeseen delays in scheduling study participation, the Qualified Investigator will determine if there is a need to ask a participant to repeat some assessments, e.g., physical examination.

Study Type

Interventional

Enrollment (Actual)

49

Phase

  • Not Applicable

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Locations

  • Canada
    • Ontario
      • Toronto, Ontario, Canada, M5S 2S1
        • Centre for Addiction and Mental Health

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

19 years to 29 years (Adult)

Accepts Healthy Volunteers

Yes

Description

Inclusion Criteria:

  • Use of cannabis at least once a week confirmed by urine point-of-care testing;
  • Males who report consuming at least 5 drinks and females who report consuming at least 4 drinks in about 2 hours in the past 6 months and at least one episode of rapid alcohol consumption in the past 6 months (3 or more drinks over a span of one hour)
  • 19-29 years of age;
  • Holds a class G or G2 Ontario driver's licence (or equivalent from another jurisdiction) for at least 12 months;
  • Willing to abstain from using alcohol for 48 hours and cannabis for 72 hours prior to Practice and Test Sessions.
  • Willing to abstain from all other drugs not prescribed for medical purposes for the duration of the study;
  • Provides written and informed consent.

Exclusion Criteria:

  • Urine toxicology screens negative for cannabis upon eligibility assessment;
  • Diagnosis of severe medical or psychiatric conditions;
  • Females: Pregnancy or breastfeeding;
  • Meets criteria for Alcohol or Substance Dependence (current or lifetime) (DSM-IV);
  • Is a regular user of medications that affect brain function (i.e., antidepressants, benzodiazepines, stimulants);
  • Taking medications or have any medical condition for which alcohol is contraindicated;
  • First-degree relative diagnosed with schizophrenia;
  • Severe allergy to citrus (lemon-lime).

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Other
  • Allocation: Randomized
  • Interventional Model: Crossover Assignment
  • Masking: Triple

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
Active Comparator: Active alcohol/active cannabis
Participant will drink an alcoholic beverage to obtain a target blood alcohol content of 0.08mg% and will smoke a delta 9 tetrahydrocannabinol (potency 12.5%) cigarette.
Drug: delta 9 tetrahydrocannabinol
A single cannabis cigarette (potency 12.5% delta 9 tetrahydrocannabinol) will be given to participants to smoke over a 10 minute period, ad libitum. If the cannabis cigarette is not smoked in its entirety, the remainder will be weighed to estimate dose.
Other Names:
  • marijuana
  • cannabis sativa
Drug: alcohol
A single oral administration of an alcoholic beverage mixed in a 1:3 ratio of alcohol to tonic water to obtain a target blood alcohol content of 0.08mg%.
Other Names:
  • ethanol
Active Comparator: Placebo alcohol/active cannabis
Participant will drink tonic water (capped with a minimal amount of alcohol to enhance alcohol cues) and will smoke a delta 9 tetrahydrocannabinol (potency 12.5%) cigarette.
Drug: delta 9 tetrahydrocannabinol
A single cannabis cigarette (potency 12.5% delta 9 tetrahydrocannabinol) will be given to participants to smoke over a 10 minute period, ad libitum. If the cannabis cigarette is not smoked in its entirety, the remainder will be weighed to estimate dose.
Other Names:
  • marijuana
  • cannabis sativa
Drug: placebo alcohol
A single oral administration of a beverage containing tonic water of the same volume as the alcoholic beverage.
Other Names:
  • tonic water
Active Comparator: Active alcohol/placebo cannabis
Participant will drink an alcoholic beverage to obtain a target blood alcohol content of 0.08mg% and will smoke a placebo delta 9 tetrahydrocannabinol (< 0.03%) cigarette.
Drug: alcohol
A single oral administration of an alcoholic beverage mixed in a 1:3 ratio of alcohol to tonic water to obtain a target blood alcohol content of 0.08mg%.
Other Names:
  • ethanol
Drug: placebo delta 9 tetrahydrocannabinol
A single placebo cannabis cigarette (<0.03% delta 9 tetrahydrocannabinol) will be given to participants to smoke over a 10 minute period, ad libitum. If the placebo cannabis cigarette is not smoked in its entirety, the remainder will be weighed to estimate dose.
Placebo Comparator: Placebo alcohol/placebo cannabis
Participant will drink tonic water (capped with a minimal amount of alcohol to enhance alcohol cues) and will smoke a placebo delta 9 tetrahydrocannabinol (< 0.03%) cigarette.
Drug: placebo alcohol
A single oral administration of a beverage containing tonic water of the same volume as the alcoholic beverage.
Other Names:
  • tonic water
Drug: placebo delta 9 tetrahydrocannabinol
A single placebo cannabis cigarette (<0.03% delta 9 tetrahydrocannabinol) will be given to participants to smoke over a 10 minute period, ad libitum. If the placebo cannabis cigarette is not smoked in its entirety, the remainder will be weighed to estimate dose.

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Psychomotor Impairment: Standard Deviation of Lateral Position
Time Frame: Alcohol exposure is Time 0. Cannabis exposure follows 15 minutes after Time 0. Driving simulation tests occur within 2 hours before and approximately 45 minutes after Time 0.
The driving simulator objectively measures changes in driving behavior after alcohol and/or cannabis exposure. Standard deviation of lateral position (SDLP) is a measure of lane control (higher SDLP indicates worse lane control).
Alcohol exposure is Time 0. Cannabis exposure follows 15 minutes after Time 0. Driving simulation tests occur within 2 hours before and approximately 45 minutes after Time 0.

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Psychomotor Impairment: Mean Speed
Time Frame: Alcohol exposure is Time 0. Cannabis exposure follows 15 minutes after Time 0. Driving simulation tests occur within 2 hours before and approximately 45 minutes after Time 0.
The driving simulator will objectively measure changes in driving behavior after alcohol and/or cannabis exposure. Mean speed during the driving scenarios is measured by the simulator.
Alcohol exposure is Time 0. Cannabis exposure follows 15 minutes after Time 0. Driving simulation tests occur within 2 hours before and approximately 45 minutes after Time 0.
Psychomotor Impairment: Standard Deviation of Speed
Time Frame: Alcohol exposure is Time 0. Cannabis exposure follows 15 minutes after Time 0. Driving simulation tests occur within 2 hours before and approximately 45 minutes after Time 0.
The driving simulator will objectively measure changes in driving behavior after alcohol and/or cannabis exposure. The simulator also (in addition to mean speed) measures standard deviation of speed.
Alcohol exposure is Time 0. Cannabis exposure follows 15 minutes after Time 0. Driving simulation tests occur within 2 hours before and approximately 45 minutes after Time 0.
Psychomotor Impairment: Maximum Speed
Time Frame: Alcohol exposure is Time 0. Cannabis exposure follows 15 minutes after Time 0. Driving simulation tests occur within 2 hours before and approximately 45 minutes after Time 0.]
The driving simulator will objectively measure changes in driving behavior after alcohol and/or cannabis exposure. The simulator measures maximum speed over the duration of the scenarios.
Alcohol exposure is Time 0. Cannabis exposure follows 15 minutes after Time 0. Driving simulation tests occur within 2 hours before and approximately 45 minutes after Time 0.]
Psychomotor Impairment: Brake Latency
Time Frame: Alcohol exposure is Time 0. Cannabis exposure follows 15 minutes after Time 0. Driving simulation tests occur at baseline and approximately 45 minutes after Time 0.
The driving simulator objectively measures changes in driving behavior after alcohol and/or cannabis exposure. During specific reaction time scenarios, participants must stop as quickly as possible after certain visual cues. The brake latency variable is measured as the mean stop/reaction time in seconds after the visual cue is presented.
Alcohol exposure is Time 0. Cannabis exposure follows 15 minutes after Time 0. Driving simulation tests occur at baseline and approximately 45 minutes after Time 0.

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Centre for Addiction and Mental Health

Collaborators

Canadian Institutes of Health Research (CIHR)
Health Canada

Investigators

  • Principal Investigator: Christine M Wickens, PhD, Centre for Addiction and Mental Health

Publications and helpful links

The person responsible for entering information about the study voluntarily provides these publications. These may be about anything related to the study.

General Publications

Helpful Links

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Actual)

July 4, 2017

Primary Completion (Actual)

January 17, 2020

Study Completion (Actual)

January 17, 2020

Study Registration Dates

First Submitted

April 4, 2017

First Submitted That Met QC Criteria

April 4, 2017

First Posted (Actual)

April 10, 2017

Study Record Updates

Last Update Posted (Actual)

July 24, 2026

Last Update Submitted That Met QC Criteria

July 23, 2026

Last Verified

March 1, 2024

More Information

Terms related to this study

Additional Relevant MeSH Terms

Other Study ID Numbers

  • 123-2015

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

NO

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

No

Studies a U.S. FDA-regulated device product

No

product manufactured in and exported from the U.S.

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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