The Impact and Detection of Driving Impairments Associated With Acute Cannabis Smoking
Condition: Cannabis Intoxication
MeSH terms: Marijuana Abuse
Study type: Interventional
Phase: Phase 1/Phase 2

Summary: 
      This study was authorized by the California Legislature (Assembly Bill 266, the Medical
      Marijuana Regulation and Safety Act to help with detection of driving under the influence of
      cannabis. One hundred and eighty healthy volunteers will inhale smoked cannabis with either
      0% (placebo), 5.9%, or 13.4% Δ9-tetrahydrocannabinol (THC) at the beginning of the day, and
      then complete driving simulations, iPad-based performance assessments, and bodily fluid draws
      (e.g., blood, saliva, breath) before the cannabis smoking and a number of times over the
      subsequent 6 hours after cannabis smoking. The purpose is to determine (1) the relationship
      of the dose of Δ9-THC on driving performance and (2) the duration of driving impairment in
      terms of hours from initial use, (3) if saliva or expired air can serve as a useful
      substitute for blood sampling of Δ9-THC, and (4) if testing using an iPad can serve as a
      useful adjunct to the standardized field sobriety test in identifying acute impairment from
      cannabis.
    

Detailed description: 
      There are several studies that suggest higher doses of whole-blood Δ9-tetrahydrocannabinol
      (Δ9-THC) concentration are associated with increased crash risk and crash culpability.
      However, attempts to define a cut-off point for blood Δ9-THC levels have proven to be
      challenging. Unlike alcohol, for which a level can be reasonably measured using a
      breathalyzer (and confirmed with a blood test), detection of a cut-off point for intoxication
      related to Δ9-THC concentration has eluded scientific verification. Recent evidence suggests
      blood Δ9-THC concentrations of 2-5 ng/mL are associated with substantial driving impairment,
      particularly in occasional smokers. Others have countered that this level leads to false
      positives, particularly in heavy cannabis users inasmuch as THC may be detectable in their
      blood specimens for 12-24 hours after inhalation. Given that 12 to 24 hours is beyond the
      likely period of driving impairment, this would appear to be a justifiable objection to a per
      se cut-off point for a Δ9-THC concentration indicative of impairment. Maximal driving
      impairment is found 20 to 40 minutes after smoking, and the risk of driving impairment
      decreases over the following hours, at least in those who smoke 18 mg Δ9-THC or less, the
      dose often used experimentally to duplicate a single joint. Other studies, however, report
      residual motor vehicle accident crash risk when cannabis is used within 4 hours prior to
      driving.

      The roadside examination using the Standardized Field Sobriety Test (SFST) for proof of
      cannabis-related impairment has not been an ideal alternative to blood levels. Originally
      devised to evaluate impairment under the influence of alcohol, the SFST is comprised of three
      examinations administered in a standardized manner by law enforcement officers. The
      'Horizontal Gaze Nystagmus' (HGN), the 'One Leg Stand' (OLS) and the 'Walk and Turn' test
      (WAT) require a person to follow instructions and perform motor activities. During the
      assessments, officers observe and record signs of impairment. In one study, Δ9-THC produced
      impairments on overall SFST performance in 50 % of the participants. In a separate study
      involving acute administration of cannabis, 30% of people failed the SFST. This discrepancy
      was thought to be in part due to the participant's cannabis use history, as well as low
      percentage of THC in the cannabis. The reported frequency of cannabis use varied from once a
      week to once every 2-6 months in the study where there was a failure on the SFST by 50% of
      the participants. The other study included more frequent users who smoked cannabis on at
      least four occasions per week.

      Based upon the above, another means is needed to help law enforcement officers discern
      driving under the influence of cannabis. One future possibility is the development of
      performance-based measures of cannabis-related impairments. This will include testing of
      critical tracking, time estimation, balance and visual spatial learning. The investigators
      have selected brief measures in order to be practicably administered repeatedly over a short
      time period, as well as tests that have the potential to translate to a field-feasible
      tablet-based format, should there be benefit in possibly including these in future
      performance-based measures for use in the field by law enforcement officers (e.g., a
      cannabis-focused field sobriety test).
    

Intervention name(s): Cannabis
Intervention type(s): Drug
Intervention description(s): Participants will smoke a cannabis cigarette ad libitum as per their usual routine
Other intervention name(s): Marijuana
Allocation: Randomized
Intervention model: Parallel Assignment
Intervention model description: Participants will be randomized to smoke a cannabis cigarette containing placebo (.02%), 5.9% or 13.4% THC.
Masking: Triple (Participant, Investigator, Outcomes Assessor)
Primary purpose: Screening
Keywords: Driving Under the Influence; Memory Impairment; Reaction Time; Time Perception; Cannabis; Marijuana; Whole Blood; Oral Fluid; Breath; Driving simulator