Field sobriety tests display insufficient accuracy for detecting THC-specific driving impairment

What is the accuracy of FSTs in identifying THC impairment? With increasing medicinal and recreational cannabis legalization, there is a public health need for effective and unbiased evaluations to determine whether a driver is impaired due to THC exposure. Though FSTs are a vital component of the gold standard law enforcement officer–based evaluations, more research must be conducted to determine their efficacy in detecting whether a person is under the influence of THC.

The critical points of the study are:

• The trial location was the Center for Medicinal Cannabis Research, University of California, San Diego.
• There were 117 men and 67 women. The adults were aged 21-55 years with cannabis use greater than or equal to 4 times in the past months. The mean age of participants was 30 years.
• A total of 184 participants were analyzed.
• Participants were randomized 1:1:1 to placebo, THC cannabis and THC cannabis smoked ad libitum.
• The primary endpoint was the law enforcement officer's determination of FST impairment at four-time points after smoking.
• One hundred twenty-one participants received THC, and 63 received a placebo.
• Officers classified 98 and 31 participants in the THC and placebo group as FST impaired at 70 minutes after smoking.
• The THC group performed significantly worse on 8 of 27 individual FST components (29.6%) and all FST summary scores compared to the placebo.
• Out Of 128 participants classified as FST impaired, officers suspected 127 (99.2%) as having received THC.
• There was a significant association between Driving simulator performance and with results of select FSTs.

Further reading:

Marcotte TD, Umlauf A, Grelotti DJ, et al. Evaluation of Field Sobriety Tests for Identifying Drivers Under the Influence of Cannabis: A Randomized Clinical Trial. JAMA Psychiatry. Published online August 02, 2023. doi:10.1001/jamapsychiatry.2023.2345