Countermeasures and Strategies to Address Cannabis-Impaired Driving; A Multi-State Survey Study

October 23, 2025

At the October CMCR Investigators’ Meeting, Dr. Linda Hill, Distinguished Professor at UC San Diego and Director of the Transportation Research and Education for Driving Safety (TREDS) program, and Sarah Hacker, Research Program Manager and Data Analyst at the Herbert Wertheim School of Public Health, presented findings from a multi-state study conducted by UC San Diego’s TREDS team in collaboration with the AAA Foundation for Traffic Safety to understand how to reach drivers who use cannabis and still get behind the wheel.

The project unfolded in three parts: interviews with national subject-matter experts; a broad, anonymous survey of 2,000 adults from eight states spanning fully legal, medicinal-only, and illegal cannabis laws; and a second survey (n ≈ 846) testing specific public-safety messages among medium- to ultra-high-risk same-day users.

Key patterns emerged. First, legality didn’t neatly predict use: self-reported cannabis prevalence was similar across legal and illegal states. Risky driving behavior was common—about half of users reported driving within an hour of use. Many believed cannabis did not worsen their driving, and a sizeable minority believed it improved it. Knowledge gaps were striking: in medicinal-only and illegal states, many participants misunderstood their state’s legal status and driving restrictions, and few cited fear of being stopped by police as influencing wait times before driving.

Message testing offered practical direction. Three messages consistently resonated: “Driving high is driving impaired,” “If you feel different, you drive different,” and “THC slows reaction time.” Pairing messages with images emphasizing consequences and community safety—along with clear alternatives such as rideshares—enhanced impact. Trust mattered: safe-driving advocates, healthcare providers, and science organizations were more credible than influencers or polarizing law-enforcement imagery. The toughest audience was the ultra-high-risk group (often younger, male, frequent users), who tended to be less trusting and more likely to feel “immune” to impairment; however, medium-risk users showed meaningful openness to changing behavior.

Bottom line: Broad, evidence-based campaigns already in use work, especially when they highlight impairment, promote alternatives to driving, and come from trusted messengers. To reduce cannabis-related crashes, prioritize targeted education in lower-knowledge states and tailor outreach to move medium-risk drivers toward safer choices.

Dr. Linda L Hill, MD, MPH
Dr. Linda L Hill, MD, MPH, is a Distinguished Professor and Founding Faculty of the Herbert Wertheim School of Public Health, where she is also Associate Dean. Dr. Hill obtained her MD from the University of Ottawa, in Ottawa, Canada in 1978 and completed a transitional internship at McGill University in 1979. She completed her residency in Preventive Medicine from the University of California San Diego (UCSD)/San Diego State University (SDSU) General Preventive Medicine Residency in 1985. She is a Fellow of the American College of Preventive Medicine. She was the founding Medical Director of the Exercise and Physical Activity Resource Center at UCSD at Qualcomm Institute. She is Faculty and immediate past Program Director of the UCSD/SDSU General Preventive Medicine Residency since 1989. San Diego Family Care, a Federal 330 Community Health Center, is the site of her clinical activities, as Medical Director 1980 to 2001, and Senior Staff Physician since 2001. She is the Director of the UCSD Training, Research and Education for Driving Safety (treds.ucsd.edu) and Co-Director of the UCSD Center for Human and Urban Mobility. She is the Executive Director of the Asylum-Seeker Shelter Health Assessment Program. Dr. Hill is engaged in prevention research and teaching, with current and past support from the NIH, the California Office of Traffic Safety, Robert Wood Johnson, American Cancer Society, Health Services Resource Administration, Caltrans, Federal Motor Carriers Service Association, and AAA Foundation for Traffic Safety, Caltrans, and the Bureau of Cannabis Control and is the author of 110+ peer reviewed papers, 4 book chapters, and 140+ abstracts. Her hobbies include classical piano and ocean sports.

Sarah Hacker 
Sarah Hacker is currently a Research Program Manager and Data Analyst at the Herbert Wertheim School of Public Health at UC San Diego. Sarah currently works with Dr. Linda Hill and TREDS (Transportation Research and Education for Driving Safety) on a variety of transportation safety projects. Her educational background is in psychology (cognition and neuroscience) and statistics, and she has used this to study driving behavior in a variety of populations. She has produced several grants, technical reports, and presentations on impaired driving, including cannabis-impaired driving.   

Resource Center for Cannabis & Cannabinoid Research
(R3CR): A Newly Funded Center

August 28, 2025

At the August CMCR Investigators’ Meeting, Mahmoud A. ElSohly, PhD, Research Professor and Professor of Pharmaceutics and Drug Delivery at the National Center for Natural Products Research in the School of Pharmacy at the University of Mississippi, and Director of the NIDA Marijuana Project, as well as President and Laboratory Director of ElSohly Laboratories Inc., introduced the newly funded Resource Center for Cannabis and Cannabinoid Research (R3CR). Supported through the NIH’s National Center for Complementary and Integrative Health (NCCIH) and in partnership with the National Institute on Drug Abuse (NIDA), the National Institute on Aging (NIA), and the National Cancer Institute (NCI), the R3CR is designed to help overcome longstanding barriers to cannabis research.

The center brings together the University of Mississippi, Washington State University, and the U.S. Pharmacopeia to provide coordinated expertise across three “cores”: regulatory guidance, research standards, and research support. Together, these groups will generate best practices, provide regulatory clarity, and disseminate resources through workshops, webinars, and an interactive website (R3CR.org).

A central feature of R3CR is its seed funding program, offering up to $50,000 annually to help investigators navigate regulatory hurdles, secure compliant infrastructure, and prepare grant applications. While funds cannot support direct clinical or laboratory research, they are intended to remove logistical roadblocks that often prevent studies from moving forward.

Dr. ElSohly emphasized that NIH created the center in response to widespread concerns from researchers about the difficulty of conducting cannabis studies—particularly with Schedule I restrictions, supply limitations, and inconsistent standards. By fostering collaboration across federally funded cannabis research centers, R3CR aims to expand access to high-quality materials, streamline compliance, and support rigorous, mechanism-driven science.

Dr. ElSohly stressed that the ultimate goal is service to the research community, ensuring that cannabis and cannabinoid science can advance with clarity, credibility, and impact.

Mahmoud A. ElSohly, PhD

Dr. ElSohly is a Research Professor and Professor of Pharmaceutics and Drug Delivery at the National Center for Natural Products Research in the School of Pharmacy at the University of Mississippi. He is the Director of the NIDA Marijuana Project and the President and Laboratory Director of ElSohly Laboratories Inc. He received his undergraduate and master’s degrees from Cairo University in Egypt and his PhD from the University of Pittsburgh School of Pharmacy. He has spent more than 50 years working on the isolation of natural products and has over 40 patents and more than 400 publications, mainly on cannabis and cannabinoids.

Dose-dependent effects of cannabidiol in social anxiety disorder:
A randomized experimental therapeutics trial 

July 24, 2025

At the July CMCR Investigators’ Meeting, Charles Taylor, PhD, Associate Professor of Psychiatry and Director, Positive Emotion & Anxiety Research Laboratory (PEARL) at UCSD presented findings from a novel randomized controlled trial that investigated the dose-dependent effects of cannabidiol (CBD) on social anxiety disorder. This Phase 2 study, funded by the NIH National Center for Complementary and Integrative Health (NCCIH), evaluated whether CBD could decrease threat reactivity and modulate plasma anandamide levels in adults with Social Anxiety Disorder (SAD).

Fifty-seven participants were randomized to receive either 300 mg or 900 mg of oral CBD or placebo for four days. Using a standardized public speaking challenge, the team measured anxiety responses through subjective distress ratings, state anxiety inventories, and self-reported negative cognitions. CBD plasma concentrations and anandamide levels were also assessed.

Findings showed that both doses of CBD reduced anxiety relative to placebo, with the 900 mg dose demonstrating more robust and consistent effects across anticipation, performance, and exploratory outcomes. A dose-response relationship was supported by both group comparisons and plasma CBD levels. However, contrary to hypotheses, CBD reduced – rather than increased – plasma anandamide levels, prompting post hoc considerations around sympathetic nervous system activity and context-dependent stress responses.

The study highlights the importance of dose selection in CBD research and provides preliminary support for advancing the 900 mg dose to longer-term trials. Although the anandamide findings were unexpected, the trial offers valuable insight into CBD’s anxiolytic potential and the complexity of cannabinoid biomarker interpretation.

This work represents one of the most rigorous trials of CBD for anxiety to date and underscores the need for targeted, mechanism-driven research in the cannabinoid space.

Charles T Taylor, PhD

Dr. Taylor is an Associate Professor of Psychiatry at UC San Diego and the Director of the Positive Emotion & Anxiety Research Laboratory (PEARL). His research over the past 20 years combines experimental psychopathology and clinical trials approaches to anxiety and depressive disorders to identify and target processes that give rise to negative emotional states or inhibit the experience of positive emotional states, with a focus on developing and optimizing intervention approaches designed to enhance social connections and well-being.

Terpenes Attenuate Pain Hypersensitivity via Indirect Engagement of CB1 Receptors Through Release of Endocannabinoids  

May 24, 2025

At the May CMCR Investigators’ Meeting, Catherine Cahill, Ph.D., a neuropharmacologist at UCLA supported by NIH funding including HEAL drug development initiatives, presented her research on the potential of cannabis-derived compounds for the treatment of chronic pain. Chronic pain affects approximately 20% of the U.S. population, and current therapies often fail to provide adequate relief, underscoring a critical unmet medical need. Dr. Cahill highlighted the high prevalence of cannabis use among individuals with chronic pain, referencing clinical data in which patients reported a 64% reduction in opioid use following cannabis substitution. Her presentation focused specifically on myrcene, a dominant terpene found in cannabis. Preclinical findings demonstrated that myrcene produced significant analgesic effects in rodent models of neuropathic pain, with anti-allodynic efficacy observed at doses of 100–200 mg/kg in males and as low as 10 mg/kg in females. Further mechanistic studies suggested that myrcene’s effects were mediated via CB1 receptor signaling, despite lacking direct receptor binding affinity. Notably, myrcene elicited sex-specific responses, producing aversive effects in females but not in males, pointing to the complexity of cannabinoid–terpene interactions in pain modulation. Ongoing investigations aim to further elucidate the pharmacodynamics of myrcene and β-caryophyllene and assess their translational potential as a non-opioid analgesic.

Catherine Cahill, Ph.D
Dr. Cahill is a neuropharmacologist who aims to advance understanding of the neurobiological mechanisms of substance use disorder and chronic pain. Her research is funded by various NIH grants including HEAL drug development proposals.