Can Field Sobriety Tests Prove Marijuana Impairment in Colorado?

When a Colorado police officer suspects drunk driving, field sobriety tests may be used to look for signs of impairment. Marijuana DUI investigations can be more complicated. Cannabis affects the body differently from alcohol, and a driver’s performance on roadside exercises does not necessarily provide a simple answer about whether marijuana impaired the person’s ability to drive.

At the Law Office of James Colgan, we defend drivers in Northglenn, Denver, and surrounding Colorado communities against DUI and DWAI charges involving marijuana and other drugs. When field sobriety tests become part of the prosecution’s evidence, we examine what the tests actually show and what other factors may explain the driver’s performance.

What Are Field Sobriety Tests?

During a DUI investigation, an officer may ask a driver to perform standardized field sobriety tests, commonly called SFSTs.

These roadside exercises can include:

Officers may observe balance, coordination, ability to follow instructions, and other behaviors while administering the tests.

Field sobriety testing is commonly associated with alcohol DUI investigations. When marijuana is suspected, however, interpreting the results can raise additional questions.

Our Denver DUI attorneys examine field sobriety tests along with chemical testing, driving behavior, officer observations, and other evidence used to support DUI or DWAI charges.

Can You Get a DUI for Marijuana in Colorado?

Yes.

Legal recreational marijuana does not make it legal to drive while impaired by marijuana.

Colorado law prohibits driving under the influence of drugs as well as alcohol. A person may therefore face DUI or DWAI allegations based on marijuana even though possessing and consuming cannabis may otherwise be lawful.

The central issue is impairment.

That distinction matters because evidence showing that someone consumed marijuana is not necessarily the same as evidence establishing how the substance affected that person's ability to operate a vehicle at the relevant time.

Are Field Sobriety Tests Designed to Detect Marijuana?

Standardized field sobriety tests have a long association with alcohol impairment investigations. Applying roadside observations to suspected cannabis impairment presents different challenges.

For example, alcohol and THC do not produce identical physiological effects.

An officer may still consider a driver's coordination, ability to follow instructions, behavior, speech, and physical appearance when investigating a suspected marijuana DUI in Northglenn.

But no individual observation should necessarily be viewed in isolation.

A driver who performs poorly on a balance exercise may have difficulty for reasons completely unrelated to marijuana.

What Else Can Cause Poor Field Sobriety Test Performance?

Roadside testing does not take place in a controlled laboratory.

Drivers may be standing beside moving traffic at night while experiencing stress from being stopped by law enforcement. Weather, lighting, pavement, physical limitations, and footwear can potentially affect performance.

Alternative explanations for poor performance can include:

The circumstances under which the officer administered the tests should therefore be examined.

Body-camera and dash-camera footage may be particularly important because the video can show the actual testing environment rather than relying solely on a written police report.

What Does the Officer Look for During a Marijuana DUI Stop?

Field sobriety exercises are only one part of a marijuana DUI investigation.

An officer may also document observations such as:

The prosecution may later attempt to combine these observations into an argument that the driver was impaired.

Each piece of evidence can also be examined individually.

For example, the presence of marijuana in a vehicle does not establish that the driver recently consumed it. Similarly, admitting to lawful marijuana use at some earlier time does not necessarily establish impairment while driving.

What Does Colorado’s 5 Nanogram THC Rule Mean?

Colorado law provides that when a driver's blood contains 5 nanograms or more of delta-9 THC per milliliter of whole blood, the fact gives rise to a permissible inference that the driver was under the influence of one or more drugs.

That is different from saying that every driver at or above 5 ng/mL is automatically impaired.

THC cases present issues that differ from alcohol cases because marijuana consumption, metabolism, frequency of use, and blood concentration do not necessarily correspond with impairment in the same straightforward way people often associate with blood alcohol concentration.

This makes the complete evidentiary picture important.

A Northglenn marijuana DUI case may involve both a blood result and the officer's observations, including field sobriety test performance.

Can You Be Charged if Your THC Level Is Below 5 ng/mL?

Potentially, yes.

A result below the 5 ng/mL threshold does not necessarily prevent prosecutors from pursuing a DUI or DWAI theory based on other evidence of impairment.

That evidence might include driving behavior, statements, officer observations, field sobriety test performance, or other circumstances.

Likewise, a THC result at or above 5 ng/mL does not mean the defense should ignore the remaining evidence.

The question remains whether the government can prove the charged offense under Colorado law.

How Can Body-Camera Video Affect a Marijuana DUI Case?

Video evidence can be particularly useful when field sobriety tests are disputed.

A police report may describe a driver as unsteady, confused, or unable to follow instructions. Body-camera footage may provide a more complete view of what happened.

Video could show whether:

Sometimes the footage supports the officer's account. In other cases, it may reveal differences between the written characterization and the driver's actual performance.

Reviewing the video rather than relying solely on the report can therefore be important in a Colorado marijuana DUI defense.

Does Having Red Eyes Prove Marijuana Impairment?

No single physical observation necessarily proves impairment.

An officer may document red or watery eyes during a suspected marijuana DUI investigation, but there can be other explanations.

Fatigue, allergies, contact lenses, dry air, smoke, and environmental irritation can all affect someone's eyes.

The same principle applies to many observations made during a traffic stop.

A driver's nervousness may reflect impairment, but it may also reflect the stress of interacting with police and worrying about arrest.

A strong DUI analysis considers alternative explanations rather than assuming every observation has only one possible cause.

What if You Use Marijuana Regularly?

Frequent marijuana use can add another issue to a Colorado DUI investigation.

THC can remain detectable after the intoxicating effects associated with consumption have diminished. Patterns of use and individual metabolism can affect test results.

This is one reason chemical evidence in marijuana cases needs to be considered in context.

The defense may examine when the blood sample was obtained, how it was collected and tested, what the result actually measured, and how prosecutors intend to connect that result to impairment while driving.

The field sobriety evidence can then be evaluated alongside those chemical results.

Can Prescription or Medical Conditions Affect the Tests?

Yes.

A driver may have legitimate physical or medical limitations that affect balance, coordination, or ability to complete roadside exercises.

Someone with an old knee injury may struggle with the one-leg stand. A person with back or hip problems may have difficulty performing the walk-and-turn. Certain neurological or balance conditions may also affect performance.

Officers may ask about physical limitations before administering tests.

Drivers charged with marijuana DUI should tell their attorney about relevant medical conditions or injuries, particularly when those conditions existed before the traffic stop.

Medical records may help document an alternative explanation for alleged signs of impairment.

What Evidence Can Be Challenged in a Marijuana DUI Case?

A marijuana DUI defense can involve much more than field sobriety tests.

Depending on the facts, we may examine:

No two Northglenn marijuana DUI cases are identical.

A driver with a high THC result but little observable evidence of impairment presents different issues from someone accused primarily because of driving behavior and roadside observations.

Why Marijuana DUI Evidence Requires Careful Review

Marijuana DUI cases can be particularly fact-dependent because there is no single roadside observation that conclusively establishes cannabis impairment.

Field sobriety tests may become part of the government's evidence, but their significance should be evaluated alongside the driver's physical condition, testing environment, officer's administration of the exercises, video footage, chemical results, and other evidence.

At the Law Office of James Colgan, we scrutinize the details rather than assuming that poor performance on a roadside exercise automatically establishes marijuana impairment.

Contact the Law Office of James Colgan About a Marijuana DUI

Field sobriety tests can provide evidence in a Colorado marijuana DUI investigation, but they do not necessarily prove by themselves that a driver was impaired by cannabis. The circumstances surrounding the testing and the rest of the prosecution's evidence matter.

If you are dealing with a marijuana DUI or DWAI charge in Northglenn, Denver, or a surrounding Colorado community, our attorneys are here to help. Call us today or connect with us online to schedule a consultation.