Driving High Comes with Real Consequences
As marijuana becomes legal across more states, the conversation often focuses on regulation, social justice, and taxation. But one issue continues to grow in urgency — driving under the influence of THC.
A recent study from Wright State University and the Journal of the American College of Surgeons found that nearly 42% of deceased drivers in fatal crashes tested positive for THC, with an average blood level of 30.7 ng/mL — six times higher than the impairment threshold used in many states (Fox News, Science Daily).
At Simmrin Law Group, our California car accident lawyers see firsthand how drug-impaired driving devastates families. Below, we explore what the research reveals, how THC affects driving, and what legal options victims have when marijuana contributes to a serious crash.
The Ohio Study: A Sobering Wake-Up Call
Between January 2019 and September 2024, researchers analyzed toxicology data from 246 deceased drivers in Montgomery County, Ohio. The results were stunning:
- 41.9% tested positive for THC (103 drivers)
- Average blood concentration: 30.7 ng/mL
- Before legalization: 42.1% tested positive
- After legalization: 45.2% tested positive (Science Daily)
Even after marijuana became legal in Ohio, fatal crash rates involving THC did not decrease. In fact, they crept upward.
According to the study authors, the high average THC levels indicate recent use rather than leftover traces from previous consumption. The findings echo what national data already show — marijuana-impaired driving is on the rise and has become a significant factor in roadway fatalities.
How THC Affects Driving
THC (tetrahydrocannabinol) interacts with the brain’s cannabinoid receptors, impairing the parts responsible for reaction time, coordination, and judgment.
Research published in Accident Analysis & Prevention found that drivers under the influence of THC are twice as likely to cause a collision as sober drivers (ScienceDirect).
A Hazelden Betty Ford review reached similar conclusions, noting that cannabis users experience:
- Slower reaction times
- Difficulty staying in their lane
- Poor judgment of speed and distance
- Reduced ability to handle unexpected events (Hazelden Betty Ford)
When alcohol is added, the danger multiplies. According to the National Highway Traffic Safety Administration (NHTSA), mixing marijuana and alcohol increases crash risk fivefold.
Simulator Studies
Driving-simulator tests consistently show that THC-impaired drivers:
- Brake later
- Drift out of lanes more often
- Overcorrect when steering
- Underestimate impairment severity
Even frequent users — who may not “feel high” — still exhibit measurable declines in coordination and divided attention for several hours after use.
Legalization Doesn’t Equal Safety
The American College of Surgeons warns that legalization can create a false sense of security. Cannabis may be legal to possess, but driving while high remains illegal in all 50 states.
Dr. Gary LeRoy of Wright State University, who co-authored the study, told reporters, “Legalization hasn’t made people safer. It’s normalized behaviors that still lead to deadly outcomes.”
Nationwide, the NHTSA reports that cannabis use is now detected in nearly one-quarter of fatal crashes — double the rate seen a decade ago.
How States Handle Marijuana-Impaired Driving
Marijuana DUI laws vary widely. The Governors Highway Safety Association (GHSA) tracks two main legal standards:
- Zero-tolerance laws – Used in 10 states (e.g., Georgia, Iowa, Michigan). Any measurable THC in your system can result in a DUI charge.
- Per-se limits – About 8 states, including Colorado, set a numeric threshold (usually 5 ng/mL). Testing above that limit creates a legal inference of impairment.
- Behavior-based evidence – In states like California, prosecutors rely on police observations, field sobriety results, and expert toxicology testimony because no numeric limit exists. (GHSA)
Scientific and Legal Challenges
Unlike alcohol, THC doesn’t have a simple correlation between blood level and impairment. A 2014 review in Forensic Science International explained that “individual tolerance, consumption method, and metabolism make establishing fixed limits scientifically fraught” (PubMed Central).
This means both prosecutors and defense attorneys must rely heavily on expert witnesses to interpret toxicology results — an area where experienced trial lawyers make all the difference.
Civil Liability in THC-Related Crashes
For Injury Victims
When a driver causes a crash while impaired by cannabis, victims may pursue a personal injury claim under theories of negligence or recklessness.
Under California law, driving while under the influence violates the duty of reasonable care. Toxicology evidence showing THC in the driver’s blood can help establish fault, even if prosecutors never file criminal DUI charges.
Because civil cases require only a preponderance of evidence (more likely than not), the standard is easier to meet than “beyond a reasonable doubt.”
For Families in Fatal Cases
If a marijuana-impaired driver kills another motorist or pedestrian, surviving family members can pursue a wrongful death lawsuit. Key evidence may include:
- Police reports and crash reconstruction data
- Toxicology results (THC, alcohol, other drugs)
- Witness statements and traffic-camera footage
- Expert testimony connecting impairment to causation
Insurance Complications
Insurers often dispute claims when intoxication is involved. They may attempt to:
- Deny liability coverage
- Reduce settlement values
- Argue the insured was solely responsible for the crash
This is why having legal representation familiar with drug-impaired accident claims is vital. Attorneys can challenge lowball settlements and use expert evidence to secure full compensation.
Broader Research on Cannabis and Driving Risk
Beyond Ohio, data nationwide show a consistent trend.
- The AAA Foundation for Traffic Safety found that 70% of cannabis users admitted to driving within an hour of use, and nearly half believed it did not impair them (AAA Foundation).
- A 2022 University of British Columbia study observed a 4.2% rise in crash rates across Canadian provinces after legalization.
- A 2024 arXiv.org study developed an eye-tracking system capable of identifying cannabis impairment with 89% accuracy, a technology that may shape future roadside testing (arXiv).
The combined evidence leaves little doubt: marijuana use and safe driving rarely coexist.
Practical Guidance
For Drivers
- Never drive high. Even small doses affect reaction time and judgment.
- Don’t mix alcohol and marijuana. The combination greatly increases crash risk.
- Wait before driving. THC effects can last several hours depending on dose and delivery method.
- Understand your state laws. California has no numeric limit but prohibits impaired driving under any influence.
- Plan ahead. Arrange a rideshare, public transit, or a sober driver.
For Victims and Families
If you suspect marijuana contributed to your crash:
- Report the crash immediately so law enforcement can collect samples and perform sobriety testing.
- Document the scene — photos, videos, and witness contacts.
- Preserve all evidence (vehicle damage, medical records, dash-cam data).
- Request toxicology results through your attorney.
- Contact a lawyer as soon as possible. THC dissipates quickly, so early action helps preserve key evidence.
How Simmrin Law Group Can Help
THC-related accidents are complex, requiring both criminal law knowledge and personal injury expertise. The attorneys at Simmrin Law Group handle both sides of these cases.
We:
- Conduct independent investigations and preserve toxicology evidence
- Work with forensic experts in pharmacology and accident reconstruction
- Challenge weak or delayed drug testing procedures
- Represent clients in both criminal DUI defense and civil injury claims
- Fight for maximum compensation for medical expenses, lost wages, and pain & suffering
Our firm’s deep courtroom experience makes us uniquely equipped to navigate cases where marijuana impairment plays a role in serious or fatal crashes.
📞 Contact Simmrin Law Group today for a free consultation. We can help you understand your rights, build a strong case, and pursue justice.
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Conclusion
The Wright State University study revealed a shocking statistic — nearly 42% of drivers killed in crashes tested positive for THC, with average levels far exceeding typical impairment thresholds (Science Daily).
As cannabis becomes more socially accepted, public safety remains at risk when users underestimate their impairment. Whether it’s a tragic fatality or a life-changing injury, victims deserve accountability.
At Simmrin Law Group, we help families pursue justice against drug-impaired drivers and guide defendants through complex DUI accusations.
No matter which side of the case you’re on — we’re here to fight for you.