This summary is based on a paper published from our lab and available on our website through the hyperlink on the “Published Research” page (or the link below): Pabon, E., & de Wit, H. (2019). Developing a phone-based measure of impairment after acute oral ∆9-tetrahydrocannabinol. Journal of Psychopharmacology, 33(9), 1160–1169. https://doi.org/10.1177/0269881119862533
With legalization of recreational cannabis use spreading across the nation, one question remains on many minds--how can we measure cannabis-induced impairment?
Biochemical measures, like Breath Alcohol Content (BAC), do not exist for detecting cannabis use. Tools currently on the market, such as the standardized field sobriety test or cannabis/THC breathalyzers, are ineffective as roadside measurements of driving under the influence. We wish it was that easy!
This question does not have a simple answer. Prior research indicates variables such as gender, age, body mass index (BMI), age of onset of cannabis use, and frequency of use all factor into how intoxicated someone may become after using cannabis. People who use cannabis more often are less likely to feel as strong effects as an occasional user. Unfortunately, accurate and effective biochemical measures (like Breath Alcohol Content (BAC) for alcohol) do not exist for detecting cannabis use.
Tools currently on the market, such as the standardized field sobriety test or cannabis/THC breathalyzers, are ineffective as roadside measurements of driving under the influence. Elisa Pabon, a fourth-year doctoral candidate studying behavioral neuroscience in our lab, decided to take a different approach: a behavioral measurement of intoxication symptoms using a phone-based application. She took the first step in validating this novel measure by conducting two double-blind, placebo controlled clinical studies (the first of their kind).
Why not let people just smoke weed? Scientists need to maintain the same conditions across all participants in studies. Using smoked cannabis requires careful consideration of strain and standardizing how much is smoked. This would have led to far too many inaccuracies, plus our results would be restrained to that specific strain!
In the first study, participants identifying as occasional to more frequent cannabis users ingested capsules containing delta-9-tetrahydrocannabinol (THC) (0, 7.5, 15 mg doses; which produce plasma levels similar to those attained with recreational cannabis use) and completed the phone-based app measure. Neither they nor the experimenter running the study knew what drug was administered on each session, to reduce expectancies. Three sessions were conducted, one for each dose. Drug-induced impairments in cognitive performance, reaction time, and working memory were detected on standard computer-based tasks, and fine motor coordination impairment was detected on the phone-based app at the 15 mg dose of THC. These results confirmed that at least fine motor impairment due to THC intoxication could be detected via our brief phone-based app under controlled conditions!
A follow-up study was done, adapted with new knowledge from Study 1 results. The phone-based app measure was lengthened and its difficulty increased, and two new tasks were added to measure time perception and time estimation (time estimation and production are impaired under the influence of smoked cannabis and oral THC and is likely to affect driving performance. Unfortunately, the new phone-based app did not detect any consistent THC intoxication impairment. The sensitivity of the phone-based app was too low to detect impairment, most likely due to the briefness of the measure. It would require additional research to develop a sensitive tool that could accurately and effectively detect cannabis impairment, but also be brief and convenient enough to use roadside.
Furthermore, these two studies were conducted under highly controlled conditions, and each person’s intoxicated performance was compared to their own respective placebo control performance. If an app like this were to be used as a roadside sobriety test, law enforcement officers would have to compare each person’s personal baseline/sober performance to their possibly intoxicated performance to accurately determine whether driving ability was impaired. Ultimately, with additional research and field work a cannabis or THC roadside field sobriety test may one day be established and validated. For now, we have a long way to go.