Marijuana and Alcohol Effects on Driving Impairment

(Alc-NHTSA Trial)

This trial examines how marijuana and alcohol together affect driving safety. Researchers will use a driving simulator to assess the impact of different doses of THC (the active component of marijuana) and alcohol. Participants will receive either a low or high dose of THC with a set amount of alcohol, or just alcohol without THC. Individuals who have used cannabis for at least two years, regularly drink and smoke, and hold a driver's license with recent highway experience may be suitable for this trial. As an Early Phase 1 trial, the study aims to understand the initial effects of combining THC and alcohol on driving, offering participants a chance to contribute to groundbreaking research.

The trial information does not specify if you need to stop taking your current medications. However, if you have a severe substance use disorder (except for cannabis and tobacco) or certain medical conditions, you may not be eligible to participate.

Research shows that mixing THC (the active ingredient in marijuana) with alcohol can impair driving ability. At low doses of THC with alcohol, studies find that marijuana users might drive more cautiously, such as by reducing speed. However, even this combination can still impair driving, especially at night.

With higher doses of THC and alcohol, the effects become more pronounced. Research indicates that reaction times significantly slow, causing drivers to take longer to respond to road conditions. This combination also leads drivers to maintain greater distances between cars and drive at lower speeds.

Researchers are excited about this trial because it explores how different doses of THC, combined with alcohol, impact driving impairment. Unlike typical studies that look at alcohol or cannabis effects separately, this trial investigates the combined impact, which is more reflective of real-world scenarios. By including various combinations, such as low and high THC doses with alcohol, and comparing them to placebo groups, the trial aims to provide valuable insights into how these substances might impair driving abilities differently. This could lead to better-informed guidelines and safety measures for drivers who use these substances.

This trial will compare the effects of different combinations of THC and alcohol on driving impairment. Participants in one arm will receive a low dose of THC with alcohol, resulting in a BAC of 0.05, while another arm will involve a high dose of THC with the same BAC level. Additionally, some arms will administer a placebo drug with no THC, combined with alcohol at BAC levels of 0.05 and 0.08. Research has shown that using both low and high amounts of THC with alcohol can make driving unsafe. Studies find that driving is more affected when both THC and alcohol are used together than when either is used alone. Even small amounts of THC with alcohol can noticeably impair driving in tests. Higher amounts of THC with alcohol cause even more impairment, indicating a stronger effect on driving skills. These findings emphasize that THC, especially when mixed with alcohol, can greatly affect safe driving.¹⁶⁷⁸⁹