What topics does this cannabis study cover?

This study covers research on: THC.

Where was this research published?

Published in Journal of analytical toxicology on August 28, 2026.

What blood tests reveal about cannabis, alcohol and driving

Q: What did this research study find?

Blood *THC* concentrations in cases where *THC* was the only detected substance ranged from **1.1 to 72 ng/mL**.

Three-year review of tetrahydrocannabinol and alcohol blood concentrations and effects in impaired driving investigations in Ontario, Canada.

Journal of analytical toxicology • August 28, 2026 • Highly Relevant

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AI Summary

This retrospective review examined blood-test results from suspected impaired-driving investigations in Ontario between 2021 and 2023. The cases involved THC alone or THC together with alcohol, with no other findings reported in the blood samples. When THC was the only substance detected, concentrations ranged from 1.1 to 72 ng/mL, with a mean of 12 ng/mL and a median of 9.5 ng/mL.

In cases involving both substances, the mean blood THC concentration was 13 ng/mL, while the mean blood alcohol concentration was 145 mg/100 mL. Common observations included collisions, erratic driving, eyelid tremors, poor balance and coordination, and bloodshot eyes. Signs of driving impairment were observed more often when both THC and alcohol were present, underscoring the importance of considering blood results alongside Drug Recognition Expert observations rather than interpreting THC concentration in isolation.

💡 Key Findings

Blood THC concentrations in cases where THC was the only detected substance ranged from 1.1 to 72 ng/mL.

Good

70%

When THC and alcohol were both detected, the mean concentrations were 13 ng/mL of THC and 145 mg/100 mL of alcohol.

Good

70%

Impairment-related observations were more frequent when THC and alcohol were combined than when THC was detected alone.

Good

75%

Common observations included collisions, erratic driving, eyelid tremors, poor balance and coordination, and bloodshot eyes.

Good

65%

📄 Original Abstract

Driving under the influence of cannabis is a significant public safety issue. Tetrahydrocannabinol (THC), the main psychoactive compound in cannabis, can impair driving ability and when used in combination with alcohol, the level of impairment can increase. Case studies documenting blood concentrations of THC and associated observations of impairment in individuals suspected of impaired driving continue to provide important contributions to the scientific literature. Retrospective analysis was performed using data from impaired driving investigations in which THC alone, and in combination with alcohol, were the only findings in blood samples submitted to the Centre of Forensic Sciences between 2021 and 2023, inclusive. In cases where only THC was present, blood concentrations ranged from 1.1 to 72 ng/mL (mean 12 ng/mL, median 9.5 ng/mL). When both THC and alcohol were present, the mean blood THC concentration was 13 ng/mL, and the mean blood alcohol concentration was 145 mg/100 mL. The most common driving and Drug Recognition Expert (DRE) observations included collisions, erratic driving, eyelid tremors, poor balance and coordination, and bloodshot eyes. Observations of driving impairment were more frequently observed in cases where both THC and alcohol were detected in the blood. These findings provide additional data to inform the interpretation of blood THC concentrations in the context of DRE observations and suspected impaired driving investigations.