Cannabis Edibles Impaired Balance and Walking Tasks in Occasional Users But Not Frequent Users
Oral cannabis significantly impaired occasional smokers on roadside sobriety tests, with 6.4 times higher odds of impairment, while inhaled cannabis effects had dissipated by the time testing occurred 1.5-3.5 hours later.
Quick Facts
What This Study Found
This controlled study compared impairment from smoked, vaporized, and oral cannabis on standard roadside sobriety tests used in driving under the influence evaluations.
For inhaled cannabis (smoked and vaporized), no significant impairment was detected because testing occurred 1.5 and 3.5 hours after dosing, by which time peak effects had subsided.
Oral cannabis (edibles) told a different story. Because edible THC is absorbed slowly, blood concentrations were still peaking during the 1.5-3.5 hour testing window. Occasional smokers who consumed oral cannabis had 6.4 times higher odds of showing two or more impairment clues on the one-leg stand and walk-and-turn tests compared to placebo.
Among all participants, oral cannabis caused significantly larger pupils under direct lighting at both 1.5 and 3.5 hours post-dose. Blood THC and its metabolite 11-hydroxy-THC both independently predicted impairment on these tests.
Frequent cannabis users showed less impairment than occasional users, consistent with tolerance development.
Key Numbers
Oral cannabis: 6.4x higher odds of impairment in occasional users (95% CI 2.3-18.4). THC blood concentration OR for impairment: 1.3 per unit increase. 11-OH-THC OR: 1.5. Pupil dilation: 0.4-0.5 mm larger than placebo.
How They Did This
Controlled study comparing frequent and occasional cannabis smokers after placebo, smoked, vaporized, and oral cannabis (6.9% THC, ~50.4 mg). Modified Romberg balance, one-leg stand, and walk-and-turn tests administered at 1.5 and 3.5 hours. Pupil sizes measured under direct lighting.
Why This Research Matters
As edible cannabis use increases, understanding its impairment timeline is critical for driving policy. Edibles produce peak impairment 1.5-3.5 hours after consumption, a delayed window that may catch users off guard if they drive thinking the effects have not yet started.
The Bigger Picture
These findings are directly relevant to cannabis-impaired driving enforcement. Standard field sobriety tests can detect oral cannabis impairment in occasional users, but the delayed onset means drivers may be impaired well after consuming an edible, unlike alcohol where impairment onset is more predictable.
What This Study Doesn't Tell Us
Small sample size limits generalizability. Testing occurred at fixed time points that favored detecting oral but not inhaled impairment. The standardized field sobriety tests were designed for alcohol impairment and may not optimally detect cannabis effects. Only one dose was tested.
Questions This Raises
- ?Should DUI enforcement develop cannabis-specific sobriety tests?
- ?How long should users wait after consuming edibles before driving?
- ?Could blood 11-OH-THC levels serve as a more reliable impairment biomarker than THC itself?
Trust & Context
- Key Stat:
- Occasional users had 6.4x higher odds of sobriety test impairment after oral cannabis
- Evidence Grade:
- Controlled experimental study with placebo comparison and multiple administration routes. Moderate because it demonstrates effects in a controlled setting with clinically relevant endpoints.
- Study Age:
- Published in 2017.
- Original Title:
- Evaluation of divided attention psychophysical task performance and effects on pupil sizes following smoked, vaporized and oral cannabis administration.
- Published In:
- Journal of applied toxicology : JAT, 37(8), 922-932 (2017)
- Authors:
- Newmeyer, Matthew N(3), Swortwood, Madeleine J(3), Taylor, Megan E, Abulseoud, Osama A, Woodward, Thomas H, Huestis, Marilyn A
- Database ID:
- RTHC-01465
Evidence Hierarchy
Participants are randomly assigned to treatment or placebo groups to test cause and effect.
What do these levels mean? →Frequently Asked Questions
How long after eating an edible are you impaired?
This study found significant impairment on sobriety tests 1.5-3.5 hours after oral cannabis consumption, when blood THC concentrations were still peaking. This is much later than the typical peak for smoked or vaped cannabis.
Can police field sobriety tests detect cannabis impairment?
Yes, at least for oral cannabis in occasional users. The one-leg stand and walk-and-turn tests detected impairment with 6.4 times higher odds of showing multiple clues compared to placebo.
Read More on RethinkTHC
Cite This Study
https://rethinkthc.com/research/RTHC-01465APA
Newmeyer, Matthew N; Swortwood, Madeleine J; Taylor, Megan E; Abulseoud, Osama A; Woodward, Thomas H; Huestis, Marilyn A. (2017). Evaluation of divided attention psychophysical task performance and effects on pupil sizes following smoked, vaporized and oral cannabis administration.. Journal of applied toxicology : JAT, 37(8), 922-932. https://doi.org/10.1002/jat.3440
MLA
Newmeyer, Matthew N, et al. "Evaluation of divided attention psychophysical task performance and effects on pupil sizes following smoked, vaporized and oral cannabis administration.." Journal of applied toxicology : JAT, 2017. https://doi.org/10.1002/jat.3440
RethinkTHC
RethinkTHC Research Database. "Evaluation of divided attention psychophysical task performa..." RTHC-01465. Retrieved from https://rethinkthc.com/research/newmeyer-2017-evaluation-of-divided-attention
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.