IMPORTANCE Expanding cannabis medicalization and legalization increases the urgency to understand the factors associated with acute driving impairment. OBJECTIVE To determine, in a large sample of regular cannabis users, the magnitude and time course of driving impairment produced by smoked cannabis of different Δ9-tetrahydrocannabinol (THC) content, the effects of use history, and concordance between perceived impairment and observed performance. DESIGN, SETTING, AND PARTICIPANTS This double-blind, placebo-controlled parallel randomized clinical trial took place from February 2017 to June 2019 at the Center for Medicinal Cannabis Research, University of California San Diego. Cannabis users were recruited for this study, and analysis took place between April 2020 and September 2021. INTERVENTIONS Placebo or 5.9% or 13.4% THC cannabis smoked ad libitum. MAIN OUTCOMES AND MEASURES The primary end point was the Composite Drive Score (CDS), which comprised key driving simulator variables, assessed prior to smoking and at multiple time points postsmoking. Additional measures included self-perceptions of driving impairment and cannabis use history. RESULTS Of 191 cannabis users, 118 (61.8%) were male, the mean (SD) age was 29.9 (8.3) years, and the mean (SD) days of use in the past month was 16.7 (9.8). Participants were randomized to the placebo group (63 [33.0%]), 5.9% THC (66 [34.6%]), and 13.4% THC (62 [32.5%]). Compared with placebo, the THC group significantly declined on the Composite Drive Score at 30 minutes (Cohen d = 0.59 [95% CI, 0.28-0.90]; P < .001) and 1 hour 30 minutes (Cohen d = 0.55 [95% CI, 0.24-0.86]; P < .001), with borderline differences at 3 hours 30 minutes (Cohen d = 0.29 [95% CI, -0.02 to 0.60]; P = .07) and no differences at 4 hours 30 minutes (Cohen d = -0.03 [95% CI, -0.33 to 0.28]; P = .87). The Composite Drive Score did not differ based on THC content (likelihood ratio χ24 = 3.83; P = .43) or use intensity (quantity × frequency) in the past 6 months (likelihood ratio χ24 = 1.41; P = .49), despite postsmoking blood THC concentrations being higher in those with the highest use intensity. Although there was hesitancy to drive immediately postsmoking, increasing numbers (81 [68.6%]) of participants reported readiness to drive at 1 hour 30 minutes despite performance not improving from initial postsmoking levels. CONCLUSIONS AND RELEVANCE Smoking cannabis ad libitum by regular users resulted in simulated driving decrements. However, when experienced users control their own intake, driving impairment cannot be inferred based on THC content of the cigarette, behavioral tolerance, or THC blood concentrations. Participants' increasing willingness to drive at 1 hour 30 minutes may indicate a false sense of driving safety. Worse driving performance is evident for several hours postsmoking in many users but appears to resolve by 4 hours 30 minutes in most individuals. Further research is needed on the impact of individual biologic differences, cannabis use history, and administration methods on driving performance. TRIAL REGISTRATION ClinicalTrials.gov Identifier: NCT02849587.

中文翻译：

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驾驶性能和大麻使用者对安全性的认知：一项随机临床试验。

重要性 扩大大麻医疗化和合法化增加了了解与急性驾驶障碍相关的因素的紧迫性。目的 确定在大量常规大麻使用者中，不同 Δ9-四氢大麻酚 (THC) 含量的吸食大麻产生的驾驶障碍的幅度和时间过程、使用历史的影响以及感知障碍与观察到的表现之间的一致性。设计、设置和参与者这项双盲、安慰剂对照的平行随机临床试验于 2017 年 2 月至 2019 年 6 月在加州大学圣地亚哥分校药用大麻研究中心进行。这项研究招募了大麻使用者，分析发生在 2020 年 4 月至 2021 年 9 月之间。干预安慰剂或 5.9% 或 13。4% THC 大麻随意吸食。主要结果和测量 主要终点是综合驾驶评分（CDS），它包括关键驾驶模拟器变量，在吸烟前和吸烟后的多个时间点进行评估。其他措施包括对驾驶障碍和大麻使用历史的自我认知。结果 191 名大麻使用者中，118 名（61.8%）为男性，平均（SD）年龄为 29.9（8.3）岁，过去一个月平均（SD）使用天数为 16.7（9.8）天。参与者被随机分配到安慰剂组 (63 [33.0%])、5.9% THC (66 [34.6%]) 和 13.4% THC (62 [32.5%])。与安慰剂相比，THC 组在 30 分钟（Cohen d = 0.59 [95% CI，0.28-0.90]；P < .001）和 1 小时 30 分钟（Cohen d = 0.55 [95% CI，0.24-0.86]；P < .001)，在 3 小时 30 分钟时有临界差异（Cohen d = 0.29 [95% CI，-0.02 至 0.60]；P = .07），在 4 小时 30 分钟时没有差异（Cohen d = -0.03 [95% CI，-0.33 0.28]；P = .87)。尽管过去 6 个月的 THC 含量（似然比 χ24 = 3.83；P = .43）或使用强度（数量 × 频率）（似然比 χ24 = 1.41；P = .49），综合驱动评分没有差异吸烟后血液中 THC 浓度在使用强度最高的人群中更高。尽管在吸烟后立即开车犹豫不决，但越来越多的参与者 (81 [68.6%]) 报告说，尽管表现没有从最初的吸烟后水平改善，但他们愿意在 1 小时 30 分钟后开车。结论和相关性 普通用户随意吸食大麻会导致模拟驾驶减量。然而，当有经验的用户控制自己的摄入量时，不能根据香烟的 THC 含量、行为耐受性或 THC 血液浓度来推断驾驶障碍。参与者越来越愿意在 1 小时 30 分钟内开车，这可能表明对驾驶安全的错误认识。许多用户在吸烟后几个小时内的驾驶性能明显下降，但在大多数人中似乎在 4 小时 30 分钟后消失。需要进一步研究个体生物学差异、大麻使用历史和给药方法对驾驶性能的影响。试验注册 ClinicalTrials.gov 标识符：NCT02849587。在 1 小时 30 分钟内驾驶的意愿增加可能表明对驾驶安全的错误认识。许多用户在吸烟后几个小时内的驾驶性能明显下降，但在大多数人中似乎在 4 小时 30 分钟后消失。需要进一步研究个体生物学差异、大麻使用历史和给药方法对驾驶性能的影响。试验注册 ClinicalTrials.gov 标识符：NCT02849587。在 1 小时 30 分钟内驾驶的意愿增加可能表明对驾驶安全的错误认识。许多用户在吸烟后几个小时内的驾驶性能明显下降，但在大多数人中似乎在 4 小时 30 分钟后消失。需要进一步研究个体生物学差异、大麻使用历史和给药方法对驾驶性能的影响。试验注册 ClinicalTrials.gov 标识符：NCT02849587。