Alcohol impairment has a number attached to it. An alcohol concentration of 0.08 is a legal threshold, and a breath or blood machine produces a figure a jury can hold on to.
Drugs have no equivalent. There is no per se limit for prescription medication, cannabis, or a controlled substance in Texas, and no roadside device that measures impairment. What fills that gap is a 12-step evaluation performed by an officer trained as a Drug Recognition Expert, which ends in an opinion — his opinion — about whether you were impaired and by what category of drug.
If you are facing a drug-related DWI, understanding where that opinion comes from is not academic. It is the case.
Why Drug DWI Cases Work Differently
Texas Penal Code § 49.01 defines intoxication two ways: not having the normal use of mental or physical faculties by reason of a substance, or an alcohol concentration of 0.08 or more. Only the second is a number.
In a drug case the State proceeds under the first definition, which means the entire question becomes whether you had lost the normal use of your faculties — and the evidence for that is observation and opinion rather than measurement. Our article on DWI charges that do not involve alcohol covers that threshold in general terms; this one is about the procedure built on top of it.
What a Drug Recognition Expert Actually Is
The Drug Evaluation and Classification programme is coordinated by the International Association of Chiefs of Police with support from the National Highway Traffic Safety Administration. Officers complete a training and certification course and are then certified as DREs.
It is worth being precise about what that credential is and is not. A DRE is a police officer who has completed a law enforcement training programme. The title contains the word "expert," but it is not a medical qualification, and the evaluation is not a diagnosis. That distinction matters enormously when the opinion reaches a jury.
The Twelve Steps
The protocol is standardised, and knowing the sequence tells you exactly when the officer is gathering observations and when he is gathering admissions:
- Breath alcohol test. If the apparent impairment is not explained by the breath result, a DRE evaluation is requested.
- Interview of the arresting officer. The DRE discusses the driving, the behaviour, and the roadside performance before ever meeting you.
- Preliminary examination and first pulse. Standard health questions, questions about recent food, alcohol, and drugs including prescriptions, observation of attitude, coordination, speech and face, a check of pupil equality and eye tracking, an initial look for horizontal gaze nystagmus, and the first of three pulse readings.
- Eye examination. Horizontal gaze nystagmus, vertical gaze nystagmus, and lack of convergence.
- Divided attention psychophysical tests. Modified Romberg Balance, Walk and Turn, One Leg Stand, and Finger to Nose.
- Vital signs and second pulse. Blood pressure, temperature, and pulse.
- Dark room examinations. Pupil size estimated under three lighting conditions using a pupilometer.
- Examination for muscle tone. Some drug categories are associated with rigidity, others with flaccidity.
- Check for injection sites and third pulse.
- Subject's statements and other observations. Miranda is typically read here, if it has not been already, followed by questions about drug use.
- Analysis and opinions of the evaluator. The DRE forms an opinion on impairment and, if impaired, on the category or categories of drug involved.
- Toxicological examination. A chemical test intended to corroborate the opinion already formed.
Notice where the questions sit. Steps 3 and 10 are the points at which you are asked to explain yourself — and step 10 is where the warning is typically given, long after step 3 has already been recorded.
Where the Evaluation Is Vulnerable
The Indicators Are Not Unique to Drugs
Nearly every observation in the protocol has innocent explanations. Elevated pulse and blood pressure follow from anxiety — and being detained at the roadside at night is a reasonably anxiety-producing event. Pupil size varies with lighting, fatigue, and medication. Balance and coordination tests are affected by injuries, inner-ear conditions, neurological conditions, obesity, age, footwear, and the surface underfoot. Diabetes, head injury, and simple exhaustion can mimic several categories at once.
The protocol contains a screen for medical conditions at step 3. Whether that screen was performed properly, and what it recorded, is frequently the most productive line of enquiry in the whole case.
Step 11 Is an Opinion, Not a Measurement
Steps 1 through 10 gather observations. Step 11 converts them into a conclusion, and that conversion happens inside the evaluating officer's judgement. There is no instrument reading at the end of it. Two certified DREs given the same subject can reach different conclusions, and the reasoning at step 11 is exactly where cross-examination belongs.
A Positive Toxicology Result Does Not Establish Impairment
This is the most important point in a drug DWI case. Many substances remain detectable in blood or urine for days or weeks after any effect has passed. Cannabis metabolites are the clearest example, but the same principle applies to prescription medication taken exactly as directed.
The State must prove you had lost the normal use of your faculties at the time you were operating the vehicle. A laboratory result confirming that a substance was present in your body does not answer that question. It is corroboration of presence, not proof of impairment — and a lawfully held prescription, taken as prescribed, does not change the analysis in the State's favour.
The Blood Draw and the Warrant Requirement
Chapter 724 of the Texas Transportation Code sets out the implied consent scheme: by driving in Texas you are deemed to have consented to testing, and refusing carries an administrative licence suspension on its own track, separate from the criminal case.
Refusal does not, however, hand the State a blood sample. In State v. Villarreal, 475 S.W.3d 784 (Tex. Crim. App. 2014), the Court of Criminal Appeals held that a warrantless, non-consensual blood draw taken under the mandatory-blood-draw and implied consent provisions violates the Fourth Amendment absent a warrant or an applicable exception. An express refusal overrides implied consent. How the specimen in your case was obtained — and whether a valid warrant supported it — is a threshold question worth litigating before anything else.
What This Means Practically
- The step 3 questions are not medical intake. They are recorded, and answers about prescriptions and recent use become evidence.
- Bring your medical history to your lawyer, not to the officer. Conditions and prescriptions that explain the indicators are defence material, and they land very differently in a suppression hearing than in a roadside admission.
- The video matters more than the report. DRE evaluations are documented on a standard face sheet that records conclusions. Footage records performance.
- Ask how the blood was obtained. Warrant, consent, or neither.
If you are facing a drug-related DWI in Collin or Denton County, our DWI defense lawyers can review the DRE face sheet, the footage, and the blood warrant together — they are rarely as consistent with one another as the offense report suggests. Contact us for a free consultation.
Frequently Asked Questions
What is a Drug Recognition Expert in Texas?
A Drug Recognition Expert is a police officer certified through the Drug Evaluation and Classification programme, coordinated by the International Association of Chiefs of Police with support from the National Highway Traffic Safety Administration. The certification comes from a law enforcement training course; it is not a medical qualification, and the DRE evaluation is not a medical diagnosis.
Is there a legal drug limit for DWI in Texas?
No. Texas sets an alcohol concentration threshold of 0.08 but has no equivalent per se limit for drugs. In a drug DWI the State proceeds under the other half of the Penal Code § 49.01 definition, proving that the driver did not have the normal use of their mental or physical faculties — which rests on observation and opinion rather than a measurement.
Can a positive drug test alone prove a Texas DWI?
No. The State must prove impairment at the time the vehicle was being operated. Many substances remain detectable in blood or urine long after any effect has passed, so a laboratory result establishes presence rather than impairment. Holding a valid prescription and taking it as directed does not change what the State has to prove.
Can a DRE evaluation be challenged in court?
Yes. Steps 1 through 10 gather observations; step 11 is where the officer converts them into a conclusion, and that conclusion is opinion testimony. Medical conditions, injuries, fatigue, anxiety, lighting, and footwear can all produce the same indicators the protocol treats as signs of drug impairment, and how the medical screen at step 3 was conducted is often the strongest line of enquiry.
Can police take your blood without a warrant in Texas after a refusal?
Generally no. In State v. Villarreal, 475 S.W.3d 784 (Tex. Crim. App. 2014), the Court of Criminal Appeals held that a warrantless, non-consensual blood draw under the implied consent and mandatory-blood-draw provisions violates the Fourth Amendment without a warrant or an applicable exception. An express refusal overrides implied consent, though the refusal still carries a separate administrative licence suspension.