title: Cannabis effects on driving lateral control with and without alcohol.
abstract: BACKGROUND
  Effects of cannabis, the most commonly encountered non-alcohol drug in driving under the influence cases, are heavily debated. We aim to determine how blood Δ(9)-tetrahydrocannabinol (THC) concentrations relate to driving impairment, with and without alcohol.
  
  
  METHODS
  Current occasional (≥1×/last 3 months, ≤3days/week) cannabis smokers drank placebo or low-dose alcohol, and inhaled 500mg placebo, low (2.9%)-THC, or high (6.7%)-THC vaporized cannabis over 10min ad libitum in separate sessions (within-subject design, 6 conditions). Participants drove (National Advanced Driving Simulator, University of Iowa) simulated drives (∼0.8h duration). Blood, oral fluid (OF), and breath alcohol samples were collected before (0.17h, 0.42h) and after (1.4h, 2.3h) driving that occurred 0.5-1.3h after inhalation. We evaluated standard deviations of lateral position (lane weave, SDLP) and steering angle, lane departures/min, and maximum lateral acceleration.
  
  
  RESULTS
  In N=18 completers (13 men, ages 21-37years), cannabis and alcohol increased SDLP. Blood THC concentrations of 8.2 and 13.1μg/L during driving increased SDLP similar to 0.05 and 0.08g/210L breath alcohol concentrations, the most common legal alcohol limits. Cannabis-alcohol SDLP effects were additive rather than synergistic, with 5μg/L THC+0.05g/210L alcohol showing similar SDLP to 0.08g/210L alcohol alone. Only alcohol increased lateral acceleration and the less-sensitive lane departures/min parameters. OF effectively documented cannabis exposure, although with greater THC concentration variability than paired blood samples.
  
  
  CONCLUSIONS
  SDLP was a sensitive cannabis-related lateral control impairment measure. During drive blood THC ≥8.2μg/L increased SDLP similar to notably-impairing alcohol concentrations. Despite OF's screening value, OF variability poses challenges in concentration-based effects interpretation.
authors.affiliation: Chemistry and Drug Metabolism, Intramural Research Program, National Institute on Drug Abuse, NIH, 251 Bayview Boulevard Ste 200 Rm 05A721, Baltimore, MD, USA; Program in Toxicology, University of Maryland Baltimore, 660 West Redwood Street, Baltimore, MD, USA.
authors.forename: Rebecca L
authors.initials: RL
authors.lastname: Hartman
authors.affiliation: National Advanced Driving Simulator, University of Iowa, 2401 Oakdale Boulevard, Iowa City, IA, USA.
authors.forename: Timothy L
authors.initials: TL
authors.lastname: Brown
authors.affiliation: College of Pharmacy, University of Iowa, Iowa City, IA, USA.
authors.forename: Gary
authors.initials: G
authors.lastname: Milavetz
authors.affiliation: College of Pharmacy, University of Iowa, Iowa City, IA, USA.
authors.forename: Andrew
authors.initials: A
authors.lastname: Spurgin
authors.affiliation: Variable Solutions, USA.
authors.forename: Russell S
authors.initials: RS
authors.lastname: Pierce
authors.affiliation: Chemistry and Drug Metabolism, Intramural Research Program, National Institute on Drug Abuse, NIH, 251 Bayview Boulevard Ste 200 Rm 05A721, Baltimore, MD, USA; Department of Psychiatry, University of Maryland School of Medicine, Baltimore, MD, USA.
authors.forename: David A
authors.initials: DA
authors.lastname: Gorelick
authors.affiliation: Carver College of Medicine, University of Iowa, Iowa City, IA, USA.
authors.forename: Gary
authors.initials: G
authors.lastname: Gaffney
authors.affiliation: Chemistry and Drug Metabolism, Intramural Research Program, National Institute on Drug Abuse, NIH, 251 Bayview Boulevard Ste 200 Rm 05A721, Baltimore, MD, USA. Electronic address: mhuestis@intra.nida.nih.gov.
authors.forename: Marilyn A
authors.initials: MA
authors.lastname: Huestis
mesh_terms: D000280:Administration, Inhalation; D000328:Adult; D001334:Automobile Driving; D001944:Breath Tests; D003198:Computer Simulation; D013759:Dronabinol / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D004347:Drug Interactions; D000431:Ethanol / Q000494:pharmacology*; D005260:Female; D006801:Humans; D008297:Male; D008385:Marijuana Smoking / Q000009:adverse effects* / Q000097:blood; D011597:Psychomotor Performance / Q000187:drug effects*; D055815:Young Adult
chemical_list: D000431:Ethanol; D013759:Dronabinol
keywords: Alcohol; Cannabis; Driving; Lateral control; Oral fluid; THC