Evaluation of divided attention psychophysical task performance and effects on pupil sizes following smoked, vaporized and oral cannabis administration

J Appl Toxicol. 2017 Aug;37(8):922-932. doi: 10.1002/jat.3440. Epub 2017 Jan 31.


Establishing science-based driving per se blood Δ9 -tetrahydrocannabinol (THC) limits is challenging, in part because of prolonged THC detection in chronic, frequent users. Therefore, documenting observable signs of impairment is important for driving under the influence of drugs. We evaluated frequent and occasional cannabis smokers' performance on the modified Romberg balance, one leg stand (OLS), and walk and turn (WAT) tasks, and pupil size effects following controlled placebo (0.001% THC), smoked, vaporized and oral (6.9% [~50.4 mg] THC) cannabis administration. Significant effects following inhaled doses were not observed due to delayed tasks administration 1.5 and 3.5 h post-dose, but significant impairment was observed after oral dosing (blood THC concentrations peaked 1.5-3.5 h post-dose). Occasional smokers' odds of exhibiting ≥2 clues on the OLS or WAT following oral dosing were 6.4 (95% CI 2.3-18.4) times higher than after placebo, with THC and 11-hydroxy-THC blood concentrations individually producing odds ratios of 1.3 (1.1-1.5) and 1.5 (1.3-1.8) for impairment in these tasks, respectively. Pupil sizes after oral dosing under the direct lighting condition were significantly larger than after placebo by mean (SE, 95% CI) 0.4 (0.1, 0.2-0.6) mm at 1.5 h and 0.5 (0.2, 0.2-0.8) mm at 3.5 h among all participants. Oral cannabis administration impaired occasional cannabis users' performance on the OLS and WAT tasks compared to placebo, supporting other reports showing these tasks are sensitive to cannabis-related impairment. Occasional smokers' impairment was related to blood THC and 11-hydroxy-THC concentrations. These are important public health policy findings as consumption of edible cannabis products increases. Published 2017. This article is a U.S. Government work and is in the public domain in the USA.

Trial registration: ClinicalTrials.gov NCT02177513.

Keywords: Drug Evaluation and Classification Program; cannabis; edibles; modified Romberg balance; one leg stand; performance; pupil size; walk and turn.

Publication types

  • Randomized Controlled Trial
  • Research Support, N.I.H., Intramural

MeSH terms

  • Administration, Oral
  • Adolescent
  • Adult
  • Attention / drug effects*
  • Cannabis / adverse effects*
  • Double-Blind Method
  • Humans
  • Inhalation Exposure
  • Marijuana Smoking / adverse effects*
  • Marijuana Smoking / psychology
  • Middle Aged
  • Psychomotor Performance / drug effects*
  • Pupil / drug effects*
  • Substance Abuse Detection / methods*
  • Task Performance and Analysis
  • Volatilization
  • Walking
  • Young Adult

Associated data

  • ClinicalTrials.gov/NCT02177513