New study reveals that THC is involved in over 40% of fatal crashes in the U.S.

Nearly half of deadly crashes involve high-THC driving, new data reveals, according to The Texas Law Dog, a law firm.

• 41.9% of deceased drivers were THC positive; mean THC 30.7 ng/mL.
• THC positivity did not decline after legalization from 2019 to 2024.
• Concentrations often exceeded the per se lines of 1–5 ng/mL used by several states.
• Legalization links to injury crashes up 6.5% and fatal crashes up 2.3%; legalization plus retail averages 5.8% injury and 4.1% fatal increases.
• Washington reports 55.1% of THC-positive fatals at or above 5 ng/mL, and about 44% also BAC 0.08 or higher; Colorado shows 15.0–18.6% drive within two to three hours of use.

If one number could change road safety coverage, it is 41.9. That is the percentage of fatally injured drivers who tested positive for THC in a new national study. Their average concentration was 30.7 ng/mL. 

The Texas Law Dog reveals these results because those levels are much higher than the common legal limits of 1 to 5 ng/mL. This means the drivers had recently and significantly used cannabis, aka marijuana.

Legalization did not reduce THC positivity during the study period. After legalization, injury crashes increased by about 6.5%. Fatal crashes increased by about 2.3%.

In Washington, 55.1% of THC-positive fatalities showed 5 ng/mL or higher. About 44% of these cases also involved a blood alcohol concentration of 0.08 or more. 

In Colorado, surveys show that 15 to 18.6% of users still drive within 2 to 3 hours of using cannabis.

High-THC Fatal Crash Analysis:

THC-positive among deceased drivers:

A new ACS Clinical Congress analysis found that 41.9% of fatally injured drivers tested positive for active THC between 2019 and 2024. The share did not decline after recreational legalization. This shows that legalization alone did not reduce cannabis-related driving risk. For reporters, tracking “THC positivity over time” is an important metric to request from county medical examiners and state crash units.

Mean THC concentration in fatal cases:

Among THC-positive drivers, the average concentration was 30.7 ng/mL. This is far above the common legal limits of 1–5 ng/mL and Colorado’s 5 ng/mL standard. Such high levels suggest recent and meaningful cannabis use, not leftover traces. Reporters can shift coverage from a simple “positive or negative” test to a story focused on both concentration and context.

Injury crash change after legalization:

Multi-state studies by IIHS and HLDI show that recreational legalization is linked to a 6.5% average increase in injury crashes. The change varies by state, from a 7% decrease to an 18% increase. This gives reporters a local angle; why did some states manage the risk better? Factors may include stronger testing, more trained officers, and better public education.

Fatal crash change after legalization:

The same research shows fatal crashes increased by about 2.3% after legalization. The rise is small but steady. Reporters should track these fatal crashes every quarter, especially during nights and weekends when impaired driving is most common.

Legalization plus retail effect:

When legalization and retail sales began together, injury crashes rose by 5.8% and fatal crashes by 4.1%. Retail markets appear to increase risk more than law changes alone. Reporters can compare crash data before and after retail openings in their state. They can also check if enforcement or public health campaigns grew at the same time.

Driving within two to three hours of use:

Colorado surveys show that 15–18.6% of cannabis users drove within 2 to 3 hours of using. This pattern stayed stable from 2019 to 2023. That 2 to 3 hour window is the key prevention target for messages, rideshare offers, or event-night campaigns.

THC ≥5 ng/mL among THC-positive fatals:

In Washington, 55.1% of THC-positive fatal crashes involved levels of 5 ng/mL or higher. Reporting on these concentrations, not just positive results, helps explain the difference between small traces and impairment-level use. Policymakers and prosecutors can use this data to refine laws and outreach.

Alcohol + THC co-positives:

About 44% of THC-positive fatal crashes in Washington also involved a blood alcohol level of 0.08 or higher. Mixing alcohol and THC greatly increases crash severity. This is a clear enforcement and messaging target, especially for nights and weekends.

The risk is no longer hypothetical. It is real, measurable, and growing where it concentrates. A 41.9% THC positivity rate with a 30.7 ng/mL average shows clear cannabis exposure in fatal crashes. After legalization, injury crashes rose by 6.5% and fatal crashes rose by 2.3%. These increases confirm that legalization adds a population-level risk.

The decision window for driving after use remains short. About 15–18.6% of users still drive within 2 to 3 hours of using cannabis. The most dangerous pattern is mixing alcohol and THC. Around 44% of THC-positive fatal crashes also involved a blood alcohol level of 0.08 or higher.

Newsrooms should press agencies for detailed toxicology data and co-positive reporting. Without this, the public will only see basic dashboards that hide where the real harm occurs. Early coverage can create a strong advantage. Reporters can secure exclusive datasets, highlight cases with THC levels of 5 ng/mL or high-density share credits, or point-of-sale safety prompts.

Quote from Texas Law Dog:

“When we see a mean THC concentration of 30.7 ng/mL in fatal crash cases, 6 to 30 times higher than most state per se limits, we’re not talking about residual metabolites or incidental exposure. We’re looking at recent, substantial impairment that directly undermines a driver’s ability to perceive hazards, maintain lane position, and execute emergency maneuvers. Under tort law, these concentration levels become critical evidence of negligence per se in wrongful death and catastrophic injury claims, particularly when paired with the 44% co-occurrence of alcohol at or above 0.08 BAC.

From a liability standpoint, the 6.5% increase in injury crashes and 4.1% rise in fatal crashes post-legalization and retail expansion creates a clear foreseeability argument that courts will recognize. Plaintiffs’ attorneys can now demonstrate that both individual defendants and potentially retail operators knew or should have known that high-concentration THC products, combined with inadequate point-of-sale warnings and the absence of reliable roadside impairment testing, would proximately cause these preventable tragedies. These aren’t just statistics; they’re admissible evidence of a public safety crisis that shifts the burden of proof in personal injury litigation and strengthens statutory violation claims under state vehicle codes.”

Methodology:

• ACS Clinical Congress / Wright State: Fatal-crash toxicology, 2019–2024, n=246; THC-positive 41.9%; mean THC 30.7 ng/mL; no post-legalization decline.
• IIHS/HLDI: Multi-state comparisons; post-legalization changes +6.5% injury, +2.3% fatal; legalization+retail +5.8% injury, +4.1% fatal.
• CDC: Evidence on cannabis-related driving impairment in reaction time, coordination, attention, and decision-making.
• Colorado DOT: Statewide surveys; 15.0–18.6% of users report driving within 2–3 hours of use (2019–2023).
• Washington Traffic Safety Commission: Public dashboard