THC in Blood Is Hard to Detect After Death in Car Accidents

The role of marijuana in car accidents remains one of the most controversial aspects of legalization. A new study conducted in Colorado challenges a common belief about the dangers of marijuana on the road. Andrea Tully, a graduate researcher at the University of Colorado in El Paso County, Colorado Springs, examined blood sampling methods and THC analysis results in a hundred recently deceased individuals.

Every subject tested positive for THC, but when comparing blood drawn from different parts of the body, Tully found significant differences. She also discovered variations in THC levels between blood taken almost immediately after death and blood drawn hours or days later from the same individual.

Her findings call into question the growing body of U.S. data on fatal vehicle accidents allegedly caused by elevated THC levels.

“Reaching a verdict that people lose control on the road due to THC in their blood may be risky and reckless because of the many uncontrolled variables found in postmortem blood analyses,” Tully writes.

This Could Become a Politically Explosive Statement

Organizations fighting against legalization have done everything possible to report a supposed increase in fatal accidents due to high THC levels. This data is often based on postmortem blood samples taken from drivers after such accidents. When a driver killed in a car crash is suspected of being impaired, blood is drawn for analysis, sometimes hours or even days after death.

THC Migrates as the Body Decomposes

In her study, Tully found that delays distorted the data. The longer the interval between death and blood sampling, the higher the THC level in the blood. She explained this as a phenomenon called postmortem redistribution.

“Postmortem redistribution describes the movement of drugs in the body after death,” Tully notes, “resulting in much higher drug concentrations in the blood at autopsy than immediately after death.”

This redistribution occurs partly because organs with high concentrations of THC, such as the lungs and liver, release it into nearby blood vessels after death. THC levels also vary greatly depending on where in the body the blood is drawn. Tully found that blood samples from a single subject ranged from 2.1 ng/mL (below the legal limit) to 6.6 ng/mL (above the legal limit), depending on the sampling site. Another subject’s THC levels ranged from 2.9 ng/mL to 40.9 ng/mL.

Blood Sample Quality Affects THC Levels

The researcher also learned that the lower the quality of the blood sample, the higher the THC concentration. One poor-quality sample contained a large amount of fat, resulting in a high THC level. This is likely because THC tends to concentrate in fat cells. This fatty sample had almost three times the THC level compared to a clean blood sample taken from the same subject.

Tully’s research does not draw any conclusions about living drivers, only about the accuracy of THC levels in blood obtained from postmortem analyses. However, these findings raise questions about whether fatal accidents are truly caused by high levels of marijuana intoxication.