Among 65 frequent concentrate users, dabbing impaired arm speed and balance immediately after use, with arm speed still impaired at 1 hour. Motor impairment was poorly correlated with blood THC levels.
Driving safety researchers, employers with impairment policies, and cannabis concentrate users.
Motor impairment lasted 1+ hour and was uncorrelated with blood THC
What the researchers found
Arm speed slowed immediately and remained impaired at 1 hour post-use. Leg speed slowed at 1 hour. Balance decreased immediately but recovered by 1 hour. These effects did not differ between sexes, and acute THC blood level changes were minimally correlated with balance impairment.
Why it matters
Cannabis concentrates with up to 90% THC are increasingly popular, yet this is one of the first studies to measure motor impairment specifically from concentrate use, relevant to driving and workplace safety.
The numbers in context
65 participants. THC potency up to 90% in concentrates. Arm speed impaired at both post-use timepoints (p<0.05). Leg speed impaired at 1 hour (p=0.033). Balance impaired immediately (eyes open p=0.017, eyes closed p=0.013) but recovered at 1 hour.
How the study worked
Observational study of 65 experienced concentrate users (46% female, average 17 days/month use) assessed in a mobile lab before, immediately after, and 1 hour after ad-libitum concentrate use. Smartphone sensors measured motor performance. Venous blood THC was measured at each timepoint.
What this study cannot tell us
Naturalistic design without controlled dosing. Frequent users may have partial tolerance. The smartphone-based assessment, while novel, is not a validated clinical tool. No placebo control.
How to read the evidence
Moderate: naturalistic design with objective measures, though lacking placebo control and standardized dosing.
When this study was published
Published in 2020 in Frontiers in Psychiatry.
The bigger picture
The poor correlation between blood THC levels and motor impairment challenges the use of blood THC as a proxy for impairment, suggesting that field sobriety-type assessments may be more useful for detecting cannabis-related impairment.
Questions still open
- Are concentrate users at greater driving risk than flower users? Why does blood THC correlate poorly with motor impairment? Would infrequent users show more severe impairment?
Common questions
How long was motor impairment detected?
Why didn't blood THC predict impairment?
Read the original research
Acute Effects of Cannabis Concentrate on Motor Control and Speed: Smartphone-Based Mobile Assessment.
Frontiers in psychiatry, 11, 623672
Citation
Hitchcock, Leah N; Tracy, Brian L; Bryan, Angela D; Hutchison, Kent E; Bidwell, L Cinnamon. (2020). Acute Effects of Cannabis Concentrate on Motor Control and Speed: Smartphone-Based Mobile Assessment.. Frontiers in psychiatry, 11, 623672. https://doi.org/10.3389/fpsyt.2020.623672