Table 1.

Summary of recent experimental studies on the effects of cannabis on driving performance when cannabis was administered on-site

Study (year), design, and country	Study participants and cannabis use history	Type(s) of cannabis and route of administration (vaporized/smoked/oral)	Type of driving test and assessment	Primary driving outcome and result
Marcotte et al. (2022) [27] Randomized, doubleblind, placebo-controlled parallel trial USA	Regular cannabis users, (N = 191) Mean age: 29.9 (SD 8.3) years Regular use defined: self-reported cannabis use >4 times in the past month	5.9% THC-dominant versus 13.4% THC-dominant versus placebo (0.02% THC) Route: smoked	Simulated driving test, 25 min, 4 total Tests of simulated driving occurred pre-dose and 30 min, 1 h 30 min, 3 h 30 min, and 4 h 30 min post-dose First task: at a specified distance, modification of the Surrogate Reference task completed, requiring participants to maintain their lane position and speed in a straight roadway, while responding to a divided attention task on an iPad to the side of the dashboard Second task: at another distance, car following required participants to adjust their speed to a lead car that speeds up and slows down according to a sinusoidal wave	Crashes and change in Composite Drive Score (CDS)1 from baseline (pre-dose) Crashes ⇔ no significant differences between the 3 groups at any time point CDS ↑ THC groups had a significant decline in CDS performance ⇔ no significant differences between the 2 THC groups in change over time (groups combined for subsequent analyses) CDS at 30 min post-dose (relative to placebo) ↑ THC group performed significantly worse CDS at 1 h 30 min post-dose (relative to placebo) ↑ THC group performed significantly worse CDS at 3 h 30 min post-dose (relative to placebo) ⇔ no significant differences CDS at 4 h 30 min post-dose (relative to placebo) ⇔ no significant differences
Arkell et al. (2020) [8] Randomized, double-blind, placebo-controlled, within-subjects, crossover trial The Netherlands	Healthy occasional cannabis users, (N = 26) Mean age 23.2 (SD 2.6) years Occasional use defined: self-reported cannabis use ≤2 times/week in the past 12 months and ≥10 lifetime exposures	13.75 mg THC-dominant (THC 22% and CBD <1%) versus 13.75 mg CBD-dominant (THC <1 % and CBD 9%) versus 13.75 mg THC/CBD equivalent versus placebo (<0.2% total cannabinoid content) Route: vaporized	On-road driving test, 60 min each, 8 total Licensed driving instructor with dual access to accelerator and brake present Participants drove a specially instrumented vehicle over a 100-km highway circuit while maintaining a constant speed (95 km/h [59 mph]) and a steady lateral position in the right (lower) lane	Mean SDLP2 At 40-100 min post-dose (relative to placebo) ↑ THC alone increased SDLP ↑ THC/CBD equivalent increased SDLP ⇔ CBD alone did not alter SDLP At 240-300 min post-dose (relative to placebo) ⇔ THC alone did not alter SDLP ⇔ THC/CBD equivalent did not alter SDLP ⇔ CBD alone did not alter SDLP
Arkell et al. (2019) [13] Randomized, double-blind, placebo-controlled, within-subjects, crossover trial Australia	Healthy infrequent cannabis users, (N = 14) Mean age 27.5 (SD 4.5) years Infrequent use defined: self-reported cannabis consumption ≤ 2 times/week in the previous 3 months and ≥10 lifetime exposures	125 mg THC-dominant (11 % THC, <1% CBD) versus 125 mg THC/CBD equivalent (11 % THC, 11% CBD) versus placebo (<1% THC, <1% CBD) Route: vaporized	Simulated driving test, 30 min each, 6 total Tests of simulated driving began 30 min (T1) and 210 min (T2) post-dose First task: 5-min car-following task in which participants were required to follow and maintain a constant distance (headway) to a lead vehicle Second task: 25-min drive consisting of highway and rural segments, participants were instructed to follow spoken GPS directions and drive as they normally would	First task: SDLP, mean headway (distance to the lead vehicle), and standard deviation (SD) of headway Second task: SDLP, mean speed (MSP), and standard deviation of speed (SDSP) First task (relative to placebo) ↑ THC alone increased SDLP at T1 and T2 ↑ THC/CBD equivalent increased at T1 and T2 ⇔ THC alone did not alter mean headway at T1 and T2 THC/CBD equivalent did not alter mean headway at T1 and T2 ⇔ THC alone did not alter SD headway at T1 and T2 ⇔ THC/CBD equivalent did not alter SD headway at T1 ↑ THC/CBD equivalent increased SD headway at T2 Second task (relative to placebo) ⇔ THC alone did not alter SDLP, MSP, or SDSP at T1 and T2 ⇔ THC/CBD equivalent did not alter SDLP, MSP, or SDSP at T1 and T2
Brands et aI. (2019) [14] Randomized, double-blind, placebo-controlled, parallel-group trial Canada	Healthy young adults, regular cannabis users, (N = 91) Mean age 21.9 (2.2) years for placebo group 22.2 (1.8) for low THC group; and 22.3 (2.0) for high THC group Regular use defined: 1–4 days/ week and evidence of recent use by qualitative urine THC-COOH determination	93.75 mg active cannabis* (cigarette with approximately 93.75 mg of 12.5% THC) versus placebo (0.07 mg THC) Cannabis cigarette smoked ad libitum for 10 min * Active cannabis users split into High THC and low THC groups, based on a median split at 7.3 ng/mL blood THC concentration at +30 min (the beginning of the driving trials) Route: smoked	Simulated driving test, 3 total, at baseline (pre-consumption) and at 30 min, 24 h, and 48 h post-dose Single task condition: participants were instructed to drive as they normally would on a straightaway (i.e., straight stretch of road without any traffic control signals or other moving vehicles) with 80 km/h speed limit Dual-task condition: participants counted backward from a number between 700 and 999 × 3′s while driving	Mean speed and lateral control3 Single task condition, 30-min post-dose ↑ Mean speed differed between high THC, low THC, and placebo groups ⇔ High THC and low THC groups decreased their speed relative to placebo ⇔ High THC or low THC did not alter lateral control ⇔ No group differences at 24 h and 48 h post-dose Dual-task condition, 30-min post-dose ⇔ Mean speed and lateral control differed between high THC and low THC groups differed from placebo but not from one another ⇔ o group differences at 24 h and 48 h post-dose
Hartley et al. (2019) [16] Randomized, double-blind, crossover trial France	Healthy chronic cannabis (CC) users, (n = 15) and occasional cannabis (OC) users (n = 30) Mean age 21.5 (3.26) Chronic (CC) use defined: 1-2 joints/day Occasional (OC) use defined: 1-2 joints/week Hair sampling was performed to confirm declarative OC or CC consumption	10 mg or 30 mg THC cannabis-containing cigarette (9.8% THC mixed with 1 g of tobacco and textile-grade hemp) Route: smoked	Simulated driving test, 30-min each, 7 total A monotonous 4-lane highway, with occasional passing vehicles, speed limit signs that the participants were encouraged to observe, and gusts of wind pushing the car and requiring corrective maneuvers	To examine the relationship between the dose and concentration of inhaled THC, reaction time, and driving ability Whole blood peak THC was 2 times higher in CC than in OC for a same dose and occurred 5 min after the end of consumption. THC remained detectable only in CC after 24 h, but CC consumed more than OC. Maximal effect for reaction time was dose- and group-dependent and only group-dependent for driving performance, both being decreased and more marked in OC than in CC. Delayed decrease in vigilance and driving performance, more pronounced and lasting longer in OC than in CC.
Ogourtsova et al. (2018) [15] Randomized, within-subjects trial (assessors blinded to time since cannabis use, participants blinded to randomization sequence) Canada	Young adult recreational cannabis users, (N = 45) Mean age 20.6 (1.3) years Recreational use defined: current use at least once within past 3 months and ≤4 days/ week	100 mg THC cannabis (12.5% THC) Route: smoked	Simulated driving test? duration not stated, 4 total Four randomized sequences of driving tests: (1) no cannabis (2) 1 h post-dose (3) 3 h post-dose (4) 5 h post-dose	Performance on three Useful Field of View (UFOV) measures UFOV-1: a simple processing-speed task UFOV-2: a complex divided-attention task UFOV-3: a complex selective-attention task Up to 5 h post-dose ⇔ No effect on simple driving-related tasks (UFOV-1) ↑ Significant impairment on complex tasks (UFOV-2, UFOV-3) ⇔ Lower self-perceived driving ability and safety
Micallef et al. (2018) [28] Randomized, placebo-controlled, double-blind, crossover trial France	Moderate tobacco smokers and occasional cannabis users Simulated driving (n = 15 completed) Real driving (n = 11 completed) Occasional use defined: self-reported smoking THC <1 time/ month	20 mg THC (8% THC) and tobacco total, cannabis-containing cigarette versus Placebo cigarette (contained strong tobacco) Cigarette smoked as completely as possible (˜20 min) Route: smoked	Simulated driving test, 2 h, 2 total versus Real (on-road) driving test, 2 h, 2 total Professional driving instructor with dual access to accelerator and brake present for real driving	Inappropriate line crossings (ILC) and SDLP Simulated driving condition ↑ THC impaired driving stability ↑ THC increased ILC Real driving condition ↑ THC impaired driving stability ⇔ THC did not significantly alter ILC Simulated driving was proven to be more sensitive for demonstrating THC-induced effects on driving performances
Bosker et al. (2012) [29] Randomized, placebo-controlled, double-blind, three-way crossover trial The Netherlands	Occasional cannabis users (n = 12) and heavy cannabis users (n = 12) Occasional use defined 5-36 times/year Heavy use defined: >160 times/year	10 mg dronabinol versus 20 mg of dronabinol versus Placebo Dronabinol and placebo were given only when occasional users tested negative and heavy users positive on THC and negative on other drugs (alcohol breath test and urine drug screen) Route: oral	On-road driving test, 3 total, between 2 and 4 h post-dose Road-tracking test (1 h): subjects had to maintain a constant speed of 95 km/h (60 miles/hr) and drive as straight as possible on the right-hand lane of a primary highway Car-following test (25 min): subjects drove behind a leading vehicle on a primary highway maintaining a constant distance between vehicles during a series of speed decelerations/acceleration initiated by the experimenter in the leading vehicle	SDLP, time to speed adaptation (TSA), and performance on Standard Field Sobriety Test (SFST) Road-tracking ↑ Dronabinol increased SDLP in occasional users (relative to heavy users) Car-following ⇔ Dronabinol did not significantly increase TSA in occasional users (relative to heavy users) SFST ⇔ No significant effects of dronabinol or cannabis use history

¹A composite of standard deviation of lateral position (SDLP), standard deviation of speed, number of correct divided attention stimuli identified while driving (first task); and coherence between the participant and lead car, a correlation ranging from 0 to 1 (second task).

²Standard deviation of lateral position (SDLP) is a measure of lane weaving.

³Lateral control operationalized as the standard deviation of the absolute distance between the center of the simulated vehicle and the center of the lane in which the participant was driving.

^*Peak plasma concentrations and ranges of blood concentrations were reported inconsistently in reviewed studies and so are excluded from this summary.