A growing number of fatal crash investigations now include toxicology results that show THC in a driver’s system. Recent research shared through the American College of Surgeons reports that more than 40% of drivers who died in crashes had detectable THC, often at levels well above per se thresholds used in some states. In South Carolina, those results can also trigger criminal exposure for DUI under drugs even though the state does not use a marijuana number to presume impairment. Prosecutors can proceed if the state claims your ability to drive was materially and appreciably impaired by cannabis or any other substance.

If you are stopped or involved in a crash anywhere along the I-85 corridor or on US-123 near Clemson, the choices you make in the next hour shape your case. This guide explains how THC relates to fatal crash investigations, what South Carolina law actually requires, and the smart steps to protect yourself and your rights.

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What the New Study Adds to the Conversation

A Wright State University team reviewed 246 deceased Ohio drivers and found that nearly 42% tested positive for THC, with an average value of about 30.7 ng/mL. The authors noted that such levels strongly suggest recent use close to the time of driving. The findings are being discussed around the 2025 American College of Surgeons Clinical Congress in Chicago, which is scheduled for October 4 to October 7, 2025.

THC Numbers and “Legal Limits” Outside South Carolina

Several states use per se thresholds for THC in blood. Examples include 2 ng/mL in Ohio and Nevada and 5 ng/mL in Washington. Some jurisdictions apply zero-tolerance or a “permissible inference” approach. South Carolina does not follow a per se model for marijuana. The focus remains whether cannabis impaired driving at the time of the incident.

How THC Shows Up in Crash Investigations

• Toxicology often occurs hours after a wreck during medical care or as part of a post-incident investigation.
• THC is fat-soluble and metabolites can remain detectable long after any feeling of being “high” fades.
• A lab number does not equal impairment at the time of driving. Officers and prosecutors still have to connect the dots between the number, the timing, and real-world driving behavior.

What South Carolina Law Requires the State to Prove

South Carolina does not use a marijuana “legal limit.” Instead, the question is whether cannabis or a combination of substances impaired your driving. That means the government must rely on observations, video, timelines, field sobriety performance, and testing. You can read more about how marijuana and other drugs are treated in DUI cases here: DUI and Drug Use in South Carolina: Legal Implications

Key Evidence Points Officers Look for in a THC DUI

• Driving behavior: drifting, delayed starts, inappropriate speed, or failure to respond to traffic signals.
• Contact clues: slow speech, red or glassy eyes, odor, or admissions about recent use.
• Field sobriety tests: one-leg stand, walk-and-turn, and horizontal gaze nystagmus. Performance can be influenced by fatigue, injuries, footwear, roadside conditions, and stress.
• Chemical testing: blood or urine draws to look for THC and metabolites. The context matters, including collection time, chain of custody, storage, and the exact method the lab uses.

Implied Consent in South Carolina and What a “Refusal” Means

If an officer believes you are impaired, implied consent rules kick in. Saying no to a breath, blood, or urine test can trigger a license suspension. You have the right to challenge that suspension on tight deadlines. Learn how implied consent works and the defenses that may apply here.

Why THC Numbers Are Not the Whole Story

Unlike alcohol, THC numbers do not move in a neat, predictable curve. People absorb and eliminate cannabis differently. Regular users can show measurable levels even when sober. Edibles hit later and last longer than smoke or vapor. Without a true per se limit, South Carolina cases rise or fall on the state’s evidence of actual impairment. That is why an experienced DUI defense uses more than one angle, including video review, independent expert analysis, and rigorous lab scrutiny.

Common Issues We See in THC-Related Crash Cases

Collection Timing

If a blood draw occurs long after driving, the state must bridge that time gap with credible evidence. Delays can weaken the connection between a number and the way you were driving.

Chain of Custody and Lab Handling

Lab paperwork must be airtight. Improper labeling, storage temperature swings, or incorrect method validation can undermine results.

Video and Third-Party Witnesses

Body-cam, dash-cam, and independent witnesses often tell a fuller story. Calm, coordinated behavior can contradict a blanket claim of impairment.

Medical Explanations

Head injuries, shock, dehydration, and certain medications can mimic signs officers attribute to cannabis. Medical records and testimony can help separate symptoms from impairment.

Metabolites vs. Active THC

Some screens flag non-impairing metabolites. The details matter. An expert can explain the difference between active THC and breakdown products that say nothing about your ability to drive at the time of the crash.

What to Do After a Stop, Wreck, or Arrest in Upstate South Carolina

Stay Safe and Seek Medical Care Your health comes first. If you are injured, accept care. Medical documentation can later explain symptoms the officer wrote down as “impairment.”
Be Polite and Concise Provide license, registration, and insurance. You have the right to remain silent about drug use or where you were and what you consumed. Ask for a lawyer before answering questions about substances.
Understand Testing Decisions If an officer requests blood or urine, implied consent rules apply. Ask if the request is voluntary or mandatory, and whether a warrant exists. If a test is given, consider an independent test as soon as feasible.
Write Down Details While Fresh Note the time you last consumed any substance, when the stop occurred, road and weather conditions, and any statements made. These specifics help your lawyer reconstruct the timeline.
Protect Your License and Your Record Deadlines arrive fast. You may need to request a hearing to challenge a suspension or to seek a temporary license. Read this for an overview of penalties and timelines.

How This Differs from Alcohol DUIs

Alcohol cases often hinge on a number. Drugged driving cases rely on context. That difference creates more room to defend the case, but it also means you should act quickly to preserve evidence and get advice that fits your facts. Read this for a broader look at how South Carolina treats marijuana and other drugs in DUI cases and this overview of drug and alcohol DUI law.

What Families Should Know in Fatal-Crash Investigations

When a wreck involves serious injury or death, investigations expand. Multiple agencies may be involved. Phones, vehicles, and medical records can be examined. Loved ones should avoid speaking about substances, timing, or fault without counsel present. A respectful, careful approach helps protect your family’s rights while the legal process unfolds.

If you or someone you care about was stopped or involved in a crash where THC is suspected, get focused help now. The Bateman Law Firm defends clients in Greenville, Spartanburg, Clemson, and nearby communities. We will review the timeline, the testing, and your options so you can move forward with clarity. Contact us today.