In Colorado, where marijuana is legal for recreational use, many drivers mistakenly assume that getting behind the wheel after using cannabis—or other substances—isn’t a major offense. However, driving under the influence of drugs (DUID) is taken just as seriously as driving under the influence of alcohol. Whether you've used marijuana, prescription medication, or illegal drugs, you can be charged with a DUID if law enforcement believes your ability to drive safely is impaired.
But unlike alcohol, there’s no straightforward measurement such as blood alcohol content to determine impairment. That leaves many people wondering: how can police tell if you’re high while driving? At Datz Law Firm, we help clients throughout Louisville and beyond who are facing drug-related driving charges understand how impairment is assessed—and how to defend against it.
What Officers Observe at the Traffic Stop
The process typically begins with a traffic stop. You might be pulled over for a minor violation—swerving within your lane, driving too slowly, or forgetting to signal a turn. These simple errors can trigger an investigation if the officer suspects drug impairment.
Once contact is made, police are trained to assess your demeanor, appearance, and behavior. Some of the initial red flags that officers look for include:
- Bloodshot or watery eyes
- Unusual pupil dilation or constriction
- Slurred or delayed speech
- Erratic or overly slow movements
- Inappropriate or exaggerated emotional responses
- The scent of marijuana or other substances
These observations are used to justify further testing. While the signs might seem obvious to police, they are highly subjective—and there are many non-drug-related explanations for similar symptoms, such as fatigue, allergies, or medical conditions.
Field Sobriety Tests and Their Limitations
After initial contact, an officer may ask you to step out of the vehicle and perform a set of field sobriety tests (FSTs). These tests are meant to assess coordination, balance, and the ability to follow instructions. The three standardized tests are:
- Horizontal Gaze Nystagmus (HGN): Following a moving object with your eyes
- Walk-and-Turn: Walking heel-to-toe in a straight line and turning as instructed
- One-Leg Stand: Balancing on one leg while counting aloud
While these tests are widely used for alcohol-related DUIs, they’re not always reliable for identifying drug impairment. Cannabis, for instance, affects individuals differently and may not hinder balance or motor coordination in the same way alcohol does. Additionally, some medications can impact a person’s ability to perform these tests despite not causing actual impairment.
The Drug Recognition Expert (DRE) Evaluation
If an officer believes you’re under the influence but needs further confirmation, a Drug Recognition Expert (DRE) may be brought in. A DRE is a law enforcement officer with specialized training to evaluate impairment from various categories of drugs. Their evaluation follows a detailed 12-step process, which may include:
- Taking your pulse and blood pressure
- Checking pupil size under different lighting conditions
- Assessing muscle tone and checking for injection sites
- Conducting a second round of field sobriety tests
- Interviewing the arresting officer for background context
- Asking about your medical and drug use history
Based on these factors, the DRE provides an opinion on what type of substance may be impairing you. However, DRE assessments are not foolproof. Their conclusions are based heavily on observation and interpretation, which opens the door for bias or error.
Blood Tests and THC Levels: A Legal Gray Zone
In Colorado, a blood test showing 5 nanograms or more of delta-9 THC per milliliter can create a presumption of impairment. But this is not a definitive threshold. THC affects each person differently, and frequent cannabis users may carry elevated THC levels long after the intoxicating effects have worn off.
Other drugs, including prescription medications, do not have an established numeric limit. This means prosecutors must rely on a combination of the officer’s observations, the DRE’s report, and toxicology results to make their case. Blood test results alone may not prove actual impairment at the time of driving—especially in the absence of poor performance on physical or cognitive tests.
It’s also worth noting that blood draws must follow strict legal procedures. If a sample is taken without proper consent or outside required timelines, that evidence may be challenged in court.
Your Rights During a DUID Investigation
Even during a routine traffic stop, you have rights that should be respected. You are not required to answer questions about drug use or where you’ve been. Politely declining to provide this information is within your legal rights and can prevent you from unintentionally incriminating yourself.
You can also decline roadside sobriety tests, although doing so may lead to arrest based on the officer’s observations. If you refuse a chemical test (blood or urine), Colorado’s express consent law allows for the automatic suspension of your driver’s license. That said, this may limit the prosecution’s ability to introduce toxicology results in court, depending on the circumstances.
If you're unsure what to do during a DUID investigation, the safest move is to request legal counsel. Asking to speak to an attorney is not an admission of guilt—it’s a smart way to protect your rights and ensure you’re treated fairly.
Contact Us Today If You’ve Been Charged With Driving Under the Influence of Drugs
A DUID charge in Colorado carries serious consequences, including license suspension, fines, probation, and potential jail time. But not every arrest leads to a conviction. At Datz Law Firm, we analyze every aspect of your case—starting with the initial stop, through field evaluations, to how your blood was drawn and tested.
If you’ve been accused of driving under the influence of drugs in Louisville or the surrounding areas, you need an experienced defense attorney who understands the unique challenges of DUID cases. Contact us today for a confidential consultation and let us help you protect your future and fight for your rights.
