Eyelid Tremor Cannabis DRE: Unreliable Under Rule 702

Should Eyelid Tremor Be Used to Prove Cannabis Impairment in North Carolina?

For years, the Drug Recognition Evaluator (DRE) protocol has relied on a structured set of physical observations to evaluate suspected drug impairment. Among these, the presence of eyelid tremor has been taught as a supposed sign of recent cannabis use. In practice, that means law enforcement officers conducting roadside evaluations or testifying in court may point to an eyelid tremor as evidence supporting probable cause or impairment. But as a recent study published in Clinical Toxicology makes clear, the scientific foundation for this assumption is, at best, unproven. At worst, it is affirmatively misleading.

In a 2024 peer-reviewed clinical research article by George Sam Wang and colleagues, the authors conducted a carefully controlled, blinded study to evaluate whether eyelid tremor could reliably and accurately be identified as a marker of recent cannabis use. The conclusion was clear. Eyelid tremor does not correlate with cannabis ingestion in a scientifically defensible way. Inter-rater reliability was poor to moderate. Specificity was dismal. And perhaps most importantly for DWI defense lawyers, the entire protocol used by officers to “spot” this supposed indicator would not come close to passing scientific muster in any peer-reviewed laboratory setting.

This post examines what the study found, how the DRE protocol incorporates eyelid tremor into cannabis impairment evaluations, and why trial courts in North Carolina should view this evidence as inadmissible or, at the very least, unreliable under the standards of North Carolina vs. Torrence and North Carolina vs. Howard.

If you’re facing impaired driving charges in the Charlotte metro area, including Mecklenburg, Union, Iredell, Gaston, Lincoln, and Rowan Counties, Powers Law Firm PA may be available to help. For felony cases involving allegations of serious injury or death and vehicular homicide, we consider representation statewide on a case-by-case basis. To discuss your situation, TEXT or call 704-342-4357.

Understanding the Role of Eyelid Tremor in DRE Evaluations

The DRE protocol is a 12-step process designed to help officers identify impairment by drug category. Eyelid tremor is not assigned its own step in the DRE’s 12-part evaluation protocol. It appears as a subcomponent of the modified Romberg balance test, which is conducted during Step 6: Dark Room Examinations. 

While the Romberg test was originally developed to assess balance and divided attention, the DRE manual instructs officers to observe the subject’s closed eyelids during this phase and note whether any tremor is present. Despite the significance this observation can carry in court, the DRE manual provides no definition of what constitutes a tremor, no training videos to distinguish it from benign or medical eye movement, and no requirement for documentation by video or third-party verification.

What investigating officers (702 DRE Experts) are not given is a scientific framework for distinguishing normal eyelid movement from pathological tremor. Nor are they trained to differentiate eyelid tremor from other benign or non-drug-related eyelid motion disorders, such as blepharoclonus, essential myokymia, or psychogenic fluttering. The protocol offers no operationalized definitions, no calibration videos, and no training on differential diagnosis. Officers are instructed to observe the eyelids and make a binary decision, whether an eyelid tremor is present or absent.

This would be a problem in any field, but in the context of criminal prosecution, where liberty interests are at stake, it is unacceptable.

The Wang Study: Blinded, Controlled, and Damning

Wang et al (2024) conducted a rigorous study designed to test exactly what DRE officers claim to observe. Their team used infrared videography to record 30-second video segments of 103 participants’ closed eyelids before and after cannabis consumption. Participants were grouped by use frequency (daily, occasional, or non-use). All videos were reviewed by three trained clinicians, including specialists in neuro-ophthalmology and medical toxicology, who were blinded to both the timing of the video and the participant’s cannabis use group.

The results dismantled the assumption that eyelid tremor has diagnostic value for recent cannabis use. Across all post-smoking videos, there was no statistically significant association between cannabis consumption and the presence of eyelid tremor. In fact, cannabis users were slightly less likely to exhibit tremor than non-users, with an odds ratio of 0.75 and a 95% confidence interval from 0.25 to 2.40.

Even more damning were the metrics for accuracy:

• Sensitivity: 0.86
• Specificity: 0.18
• Overall accuracy: 0.64

In plain language, this means that while the test might catch some users, it fails to exclude non-users at an acceptable rate. The specificity is so low that a positive finding is functionally meaningless.

Just as importantly, the inter-observer agreement scores were poor. Kappa statistics, used to measure inter-rater reliability, ranged from 0.44 to 0.45. Intra-class correlation coefficients hovered around 0.58 to 0.61. 

These values indicate moderate agreement at best, and they were achieved under idealized conditions, in dark rooms, high-definition monitors, and trained medical observers.

The average roadside DRE evaluation offers none of those advantages.

• Drug-related impaired driving charges in North Carolina
• Expert testimony admissibility under Rule 702
• What kind of experts are used in drugged driving prosecutions?
• North Carolina’s application of Rule 702 in impaired driving prosecutions
• Standardized tests like HGN, walk-and-turn, and one-leg stand
• Evidence of impairment must be more than subjective officer impressions
• Criminal Evidence: Expert Testimony in North Carolina – Superior Court Bench Book

Real-World Implications: Unfounded Confidence in a Flawed Indicator of Impairment 

The DRE protocol is a law enforcement tool, not a clinical diagnostic instrument. Yet in practice, the veneer of structure and the use of medical-sounding terms create the impression of scientific legitimacy. 

When an officer testifies in a North Carolina courtroom that they observed eyelid tremor, the jury is likely to infer that this is an objective, validated marker of cannabis impairment. It is not.

The officer has not been trained to distinguish eyelid tremor from benign eyelid movement. They have not been instructed on differential causes. They have not measured amplitude, frequency, symmetry, or whether the movement is bilaterally synchronous. No video is taken. No calibration tools are used. No peer review or second opinion is available. 

The officer simply observes what they believe to be an eyelid tremor, and this observation is then used to support arrest, detention, and prosecution.

This is not just flawed. It is dangerous.

North Carolina Case Law: Scientific Evidence Must Be Reliable

North Carolina courts follow a version of Rule 702 that incorporates the Daubert standard. In North Carolina vs. Torrence, the Court of Appeals reiterated that expert testimony must be both relevant and reliable. 

When it comes to scientific evidence, this means the method must be based on sufficient facts or data and must be the product of reliable principles and methods. Moreover, the witness must have applied those principles and methods reliably to the facts of the case.

In North Carolina vs. Howard, the court evaluated the admissibility of horizontal gaze nystagmus (HGN) testing in the absence of scientific proof of reliability. The court emphasized that expert testimony based on subjective observations must be grounded in some demonstrable scientific foundation.

That same reasoning applies with even more force to the claimed observation of eyelid tremor. 

There is no data supporting its reliability as an indicator of impairment. 

Under Rule 702, this fails.

The study’s failure to show a reliable link between cannabis use and eyelid tremor directly undermines its evidentiary value in court. 

When the presence or absence of an eyelid tremor depends more on who’s watching than what the subject consumed, and when specificity drops below any meaningful forensic threshold, the result is not just scientific weakness. It’s legal unreliability. 

That distinction matters in the courtroom, where even trained officers operate without the benefit of high-resolution video, controlled lighting, or consensus scoring.

Jury Misperception and the Problem of Pseudo-Science

It is easy to imagine how a prosecutor might use an officer’s testimony about eyelid tremor to bolster their case. 

It sounds like something only trained professionals could see. It sounds like a subtle neurological tell, something that reflects real-time impairment. And it is often listed in conjunction with other physical signs, giving the appearance of a pattern.

But the scientific literature tells a different story. 

Eyelid tremor is not reliably observed, not well defined, and not specific to cannabis impairment. 

Its presence is neither predictive nor probative. Its absence tells us little, and its presence tells us nothing more.

This is not evidence. It is speculation.

What DWI Lawyers Should Do

If you’re defending a client facing drugged driving charges in North Carolina and the DRE officer mentions eyelid tremor, DWI lawyers may want to consider filing a motion in limine to exclude that testimony. 

Demand a voir dire of the officer on their training, methodology, and experience identifying neurological signs as part of the legal strategy when defending drug-related DWI cases. 

Use the Wang study to confront the scientific foundation of the observation. If the court excludes it, make a formal offer of proof. Whether through voir dire or cross-examination, be ready to show that the claimed indicator does not satisfy the evidentiary demands of Rule 702 and lacks the reliability necessary for admissibility.

You should also prepare to address the risk of prejudice. 

Jurors tend to overvalue science-sounding claims. Without a firm rebuttal, the idea of “eyelid tremor” can take on an aura of legitimacy that it does not deserve.

Flawed SFST Science Should Not Be the Basis for Criminal Prosecution

The inclusion of eyelid tremor in the DRE protocol may have originated from genuine, if anecdotal, observation. Anecdote is not science. Science now indicates that this particular indicator is highly unreliable.

Courts must serve as gatekeepers. Officers deserve better training. Jurors deserve better evidence. And defendants deserve a system that is grounded in fact, not myth.

The continued use of eyelid tremor as an indicator of cannabis impairment, particularly without video documentation or scientific substantiation, does not serve justice. It undermines it.

If you’re facing impaired driving charges in the Charlotte metro region, including Mecklenburg, Union, Iredell, Gaston, Lincoln, and Rowan Counties, the Powers Law Firm PA, may be available for legal representation. For felony allegations involving serious injury, death, or vehicular homicide, we evaluate statewide representation on a case-by-case basis. Call now 704-342-4357 to schedule a confidential consultation that is free of charge.  Learn more about our approach to impaired driving defense at Powers Law Firm PA, or browse our recent DWI defense articles.