Scientific Papers describing Impairment Science’s technology and confirming it’s accuracy and utility

  • Effects of High Potency Cannabis on Psychomotor Performance in Frequent Cannabis Users
    • Journal:  Cannabis and Cannabinoid Research (In press)
    • Institutions:  University of Colorado,Boulder; Washington State University; Impairment Science, Inc.
    • Authors:  Karoly, H. C., Milburn, M. A., Brooks-Russell, A., Brown, M., Streufert, J., Bryan, A. D., Lovrich, N. P., DeJong, W., Bidwell, L. C. (2020).  
  • Assessment of cognitive and psychomotor impairment, subjective drug effects, and blood THC concentrations following acute administration of oral and vaporized cannabis
    • Journal:  Journal of Psychopharmacology (Submitted)
    • Institution:  Johns Hopkins University School of Medicine, Behavioral Pharmacology Research Unit
    • Authors:  Spindle, T R., Martin, E.,  Grabenauer, M., Woodward, T.,  Milburn, M., & Vandrey, R. (2020

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Demonstrating the DRUID® App’s Validity

The DRUID® app is designed to assess a user’s level of cognitive and motor impairment due to any underlying cause. Informed by impairment research, the app requires users to perform four tasks that measure reaction time, accuracy of decision making, hand-eye coordination, time estimation, and balance. Importantly, three of the four tasks are divided-attention tasks.

All four tasks can be completed in just under three minutes. The app collects and statistically integrates hundreds of measurements, thereby producing an overall impairment score (T-score) ranging from 0 to 100. In practice, most T-scores fall between 30 and 70.

To use the app successfully, users must: (1) practice three or four times to learn what the four tasks require of them; (2) establish a stable baseline score, at a time when they are unimpaired; and (3) in the future, use the app to assess their level impairment against their established baseline. A typical baseline score is generally in the range of 32-42.

To demonstrate the DRUID app’s reliability, we asked a frequent cannabis user, on two successive days, to inhale a vaporized sample of marijuana (0.4 grams) taken from the same batch. This individual was an experienced DRUID user with an established stable baseline score.

As shown here, the app produced very similar scores over a span of 90 minutes. The T-scores on both days show a level of impairment that parallels users’ sub­jective experience from cannabis, with peak intoxica­tion reached in about 30 minutes, and then gradually decreasing as the body metabo­lizes the drug over time.

Validating DRUID Against Measured Blood Alcohol Concentration (BAC). Richmond and May (2019) validated DRUID® during a training session for Massachusetts police cadets. A total of 21 volunteers, ages 22 to 51, practiced the app, established their baseline score, drank alcohol until they reached a breathalyzer-measured BAC greater than 0.08%, and then immediately used the app a second time. At baseline, participants’ mean T-score was 44.3. After being dosed, their mean T-score rose to 57.3, a statistically significant result, t(47) = 8.7, p < 0.001. As shown here, the 95% confidence intervals for the pre-alcohol and post-alcohol T-score distributions do not overlap, despite the fact that the volunteers reached variable BAC levels greater than 0.08%.

Validating DRUID with Infrequent Cannabis Users. Researchers at the Johns Hopkins Medical Institute tested the DRUID app with 20 participants, ages 18-45, who were infrequent canna­bis users (Spindle et al., 2020). Participants completed six double-blind outpatient sessions, with the order of those sessions counter-balanced: a) ingested cannabis brownies containing 0, 10, and 25 mg THC, and b) inhaled vaporized cannabis containing 0, 5, and 20 mg THC.

During each session, measures of subjective, physiological, cognitive, and psychomotor effects were taken hourly for eight hours. In addition to the DRUID iOS app, the impairment measures included three computerized cognitive-psychomotor performance assessments: Digit Symbol Substitution Task (DSST), Paced Serial Addition Task (PSAT), and) Divided Attention Task (DAT); plus six field sobriety tests: horizontal gaze nystagmus, lack of eye convergence, pupillary response, walk and turn (WT), one-leg stand (OLS), and Modified Romberg Balance (MRB).

The 10 mg oral dose and the 5 mg vaporized dose produced positive subjective effects, but did not significantly impair cognitive-psychomotor performance relative to the 0 mg placebo. The 25 mg oral and 20 mg vaporized doses increased both positive and negative subjective effects, while also impairing performance on DRUID® and the other cognitive-psychomotor tasks. Importantly, the field sobriety tests were generally insensitive to cannabis-induced impairment.

The above figure displays the mean DRUID T-scores and 95% confidence intervals for the six testing sessions. In the 25 mg oral THC condition, DRUID performance was significantly impaired relative to baseline 2-5 hours after ingestion, but within the 0-1 hour period in the 20 mg vaped THC condition, as would be expected.

Spindle et al. (2020) stated that DRUID was the most sensitive measure of impairment, as indicated by finding significant differences between the placebo and higher doses for both routes of THC administration.

Validating DRUID® with Frequent Cannabis Users. Karoly et al. (2020) reported the findings of two studies with frequent cannabis users. In the Colorado study (n=70), frequent cannabis users (4+ times per week) used DRUID® to establish a sober baseline impairment score. During a second appointment, they used DRUID® at three timepoints: pre-use; immediately after acutely using cannabis; and one-hour post-use. Each participant used ad libitum one of two randomly assigned products they purchased at a local dispensary, depending on the type of cannabis they preferred: cannabis flower users (n=16) bought 3 grams of a product with either 15% or 24% THC, while concentrate users (n=54) bought 1 gram with either 70% or 90% THC.

In the Washington study (n=39), daily or near-daily cannabis users used DRUID® prior to acute cannabis consumption and then every half hour for 2.5 hours. The participants were asked to consume the amount and type of cannabis they typically used, selecting from a variety of high-THC products, either a concentrate (n=2) or flower cannabis pre-rolled into 0.5-gram “joints” (n=37; no participant used less than 1 gram).

Shown here are the mean T-scores and 95% confidence intervals for both studies. Both the Colorado and Washington studies demonstrated that frequent cannabis users who consumed products consistent with their typical use patterns had significantly increased impairment after ingesting high-potency cannabis. In both studies, impairment peaked shortly after acute use and decreased over the next hour. The external validity of these findings is enhanced by the fact that there was variability in the amount of cannabis consumed, type of cannabis (i.e., flower or concentrate), and ingestion method. 


Karoly, H. C., Milburn, M. A., Brooks-Russell, A., Brown, M., . . . Bidwell, L. C. (2020). Effects of high potency cannabis on psychomotor performance in frequent cannabis users. Manuscript submitted for publication.

Richman, J. E., & May, S. (2019).   An investigation of the Druid® smartphone/tablet app as a rapid screening assessment for cognitive and psychomotor impairment associated with alcohol intoxication.  Vision Development Rehabilitation, 5, 31-42.

Spindle, T. R., Martin, E., Grabenauer, M., Woodward, T., Milburn, M., & Vandrey, R. (2020). Assessment of cognitive and psychomotor impairment, subjective drug effects, and blood THC concentrations following acute administration of oral and vaporized cannabis. Manuscript submitted for publication.