Unveiling the Truth: Can Police Accurately Detect THC Impairment Through Field Sobriety Tests?

In the intricate dance between law enforcement and the ever-changing landscape of marijuana legalization, a new spotlight is being cast on a critical question: Can police officers accurately identify impairment caused by THC, the active component of cannabis, through the use of field sobriety tests? A recent study published in the Journal of the American Medical Association (JAMA) Psychiatry has turned this question into a focal point of discussion, revealing unsettling results that challenge conventional wisdom. As we delve into the intricacies of this study's findings, it becomes evident that the efficacy of field sobriety tests in pinpointing THC impairment might not be as solid as once thought, raising important concerns about road safety and fair law enforcement practices.

What is a Field Sobriety Test?

field sobriety test for thc

A field sobriety test (FST) is a set of standardized physical and cognitive assessments administered by law enforcement officers to determine if a person is impaired by alcohol or drugs, typically when operating a vehicle. These tests are conducted during traffic stops and are intended to help officers evaluate a driver's coordination, balance, cognitive function, and overall ability to safely operate a vehicle. FSTs are often used to gather evidence of impairment, which can then be used in legal proceedings related to driving under the influence (DUI) or driving while impaired (DWI) charges.

Common Examples of Field Sobriety Tests

can police detect thc while driving?

Horizontal Gaze Nystagmus (HGN)

In this test, an officer observes the driver's eyes as they follow a moving object, usually a pen or flashlight. Nystagmus is an involuntary jerking of the eyes, and its presence can indicate alcohol or drug impairment.


The driver is asked to take a series of steps in a straight line, touching heel-to-toe with each step. After a set number of steps, they must turn and return in the same manner. This test assesses balance, coordination, and the ability to follow instructions.

One-Leg Stand

The driver is asked to stand on one leg while counting aloud for a specified duration. This test evaluates balance and the ability to multitask.


In this test, the driver is instructed to touch their nose with their fingertip while their eyes are closed. The officer observes their ability to accurately complete the task and maintain balance.

Romberg Balance Test

The driver is asked to stand with their feet together, head tilted back, and eyes closed. The officer measures the driver's ability to maintain balance and assesses whether they can estimate the passage of a specific amount of time.

Alphabet or Counting Test

The driver may be asked to recite the alphabet or count backward, testing cognitive functions under stress.

Unveiling the Study's Findings

thc detection by police study results

The study included 184 adult cannabis users between the ages of 21 and 55. During the experiment, 63 participants received a placebo cannabis cigarette while 121 participants received a THC cannabis cigarette. Participants who consumed the THC reported a median highness level of 64 on a scale of 0 to 100, suggesting the content was sufficient to achieve significant intoxication.

Highly trained law enforcement officers then performed field sobriety tests to examine abilities such as balance, coordination, divided attention and eye movements. These include the Walk and Turn, One Leg Stand, Finger to Nose, Lack of Convergence and Modified Romberg tests. The tests were performed at four different time intervals, roughly one, two, three and four hours after smoking. Remarkably, the study uncovered that officers consistently misinterpreted FST performance, wrongly categorizing 49.2 percent of the placebo group as impaired.

The implications of these findings are far-reaching, as they question the reliability of FSTs in identifying cannabis-induced impairment. The study's authors emphasized that FSTs provide only supplementary evidence of impairment and are not robust indicators of THC-specific impairment.

A Flawed Approach to Detection

An accompanying editorial in JAMA Psychiatry pointedly criticizes the traditional reliance on FSTs as an insufficient method to detect cannabis-induced impairment. The editorial highlights that even highly trained officers struggle to accurately identify such impairment through FSTs. This revelation has potential legal consequences, given that FSTs are currently a standard evaluation protocol in North America to identify cannabis-impaired drivers.

The Promise of Technological Innovation

The inadequacies of FSTs have sparked interest in alternative methods for accurately assessing cannabis-induced impairment. The study's results resonate with those of a 2021 John Hopkins University study, which highlighted the limited sensitivity of key FST elements, such as the 'walk-and-turn' test and the one leg stand, in detecting impairment caused by THC. However, the same study acknowledged the efficacy of the mobile device performance application called DRUID, which demonstrated sensitivity to cannabis-induced changes in performance.

The advocacy group NORML has repeatedly emphasized the value of performance testing technology as a more dependable indicator of cannabis-induced impairment. This technology could provide law enforcement with effective tools to identify impairment more accurately and objectively than traditional FSTs.

Legal Precedents and Future Directions

how will the law handle thc detection during traffic stops?

The debate over FSTs and their reliability in detecting cannabis-induced impairment is not new. As far back as 2017, the Massachusetts Supreme Judicial Court ruled in Commonwealth v. Gerhardt that standard roadside FSTs cannot be treated as scientific tests for marijuana impairment. This landmark decision highlights the growing acknowledgment of the limitations of FSTs in this context.

The recent study underscores the urgent need for law enforcement agencies to reconsider their reliance on FSTs as a sole method for detecting cannabis-induced impairment. It also emphasizes the importance of investing in innovative technologies, like DRUID, which show promise in providing more accurate and objective assessments.

In conclusion, as the conversation around marijuana legalization continues to unfold, the shortcomings of traditional field sobriety tests have come to the forefront. The study's findings and the broader body of research challenge us to reevaluate our approaches to identifying cannabis-induced impairment on the road. It's clear that we need more sophisticated and reliable methods to ensure both public safety and the fair treatment of individuals in this evolving landscape.

So, What About CBD?

While field sobriety test are proving to be unreliable in accurately detecting THC impairment, it is still not recommended to drive while under the influence of cannabis. The issue of cannabis and driving may have consumers wondering about how CBD can affect driving and the legality of driving while taking CBD. 

CBD, known as cannabidiol, is a non-psychoactive compound found in cannabis, celebrated for its potential therapeutic advantages. Unlike THC, CBD doesn't induce the typical "high" or impairment associated with cannabis use.

Although research exploring the effects of CBD consumption on driving performance is limited, the available data suggests that CBD is unlikely to hinder driving abilities. A recent study highlighted in the Journal of Psychopharmacology demonstrated that even at high doses of up to 1500 mg, CBD didn't impede motor or cognitive functions in a group of healthy participants.

Nonetheless, it's crucial to acknowledge that certain CBD products might contain minute traces of THC, which could cause impairment if ingested in substantial amounts. Moreover, using CBD concurrently with other substances like drugs or alcohol could heighten the risk of impairment and should be avoided while operating a vehicle.

In a nutshell, while CBD is not assumed to impact driving negatively, it's imperative to practice prudence and responsible usage, particularly when dealing with CBD items that include THC or when paired with other substances. As with any substance, if there's even a sliver of uncertainty about your level of impairment, it's always wise to refrain from driving.

CBD and E1011 Labs

cbd heat not burn product

Those looking to explore the world of CBD can check out the products here at E1011 Labs. E1011 Labs has emerged as a vanguard in the cannabis industry, driven by a passion for reimagining the cannabis experience through technological ingenuity. At the heart of our innovation lies the elon®, a revolutionary dry herb vaporizer device that harmonizes modern technology with traditional herb consumption. The elon transcends conventional methods, utilizing heat-not-burn technology to preserve the essential compounds found in herbal materials while avoiding the harmful byproducts of combustion. This forward-thinking approach not only ensures a cleaner and more flavorful experience for users but also exemplifies our commitment to merging science and sustainability.

Central to E1011 Labs' vision is our stelo™ flower pod, a breakthrough in convenience and precision. Our stelo encapsulate the essence of carefully curated botanicals, providing users with a consistent and controlled consumption experience. Crafted with a deep understanding of nature's offerings, each stelo contains premium full spectrum hemp flower blends designed to deliver distinct effects and flavors. This innovative system empowers individuals to explore the diverse spectrum of botanical benefits with ease, embracing the future of cannabis consumption while respecting its rich heritage. E1011 Labs' dedication to pushing boundaries and their emphasis on user-centric design shine brightly through the elon device and stelo, signaling a harmonious union of tradition and technology in the cannabis realm.