DWI Drug Intoxication in Texas: What You Need to Know

Field Sobriety Tests Were Built for Alcohol, Not Drugs

You will likely be run through the same three roadside tests used in alcohol cases: the horizontal gaze nystagmus eye test, the walk-and-turn, and the one-leg stand. Here is the problem the state prefers not to discuss: those tests were developed and validated specifically to detect alcohol impairment. Their reliability for identifying drug impairment has been widely questioned by researchers and defense experts. Many substances affect the body in ways alcohol does not, and the physical cues officers are trained to look for may simply not apply to you.

The Drug Recognition Expert Evaluation, and Its Coin-Flip Problem

If the officer suspects drugs, a Drug Recognition Expert, or DRE, may be called in. The title sounds medical. It is not: a DRE is a police officer who has completed roughly 152 hours of dedicated training through the International Association of Chiefs of Police and the National Highway Traffic Safety Administration.

The DRE runs a 12-step evaluation: a breath test to rule out alcohol, an interview with the arresting officer, a preliminary examination, eye examinations checking pupil size and different types of nystagmus, divided attention tests, vital signs including pulse, blood pressure, and body temperature, an examination of muscle tone, a check for injection sites, and finally an opinion about whether you are impaired and which category of drugs caused it.

It sounds scientific. In practice, it is heavily subjective. The DRE must place any suspected drug into one of seven categories — central nervous system depressants, stimulants, hallucinogens, dissociative anesthetics, narcotic analgesics, inhalants, or cannabis — and the protocol does not allow "I don't know" as an answer. A Texas A&M study of DRE evaluations found a median accuracy rate of just 53.2%. That is barely better than a coin flip. Organizations including the ACLU and the National Association of Criminal Defense Lawyers have described the DRE protocol as inherently subjective and lacking rigorous scientific validation.

If a DRE evaluated you, do not assume the report is unbeatable. That opinion is often the centerpiece of the state's drug DWI case, and it can be taken apart question by question — the officer's training, shortcuts in the protocol, conclusions the observations do not support. Contact our Conroe office before you accept any plea: the earlier we see the DRE report, the more of it we can challenge.

A Blood Test Proves Presence, Not Impairment

Breath machines cannot detect drugs, so drug DWI cases turn on blood. Your sample goes to a forensic laboratory for toxicological analysis, and if the result comes back positive, the state will treat it as the heart of its case. But here is what that result actually shows: a blood test can confirm that a substance was present in your system. It cannot say whether you were impaired at the time you were driving. Our page on breath and blood tests in Texas DWI cases explains how these samples are collected and challenged.

That gap matters more in drug cases than anywhere else. THC, the psychoactive compound in marijuana, can remain detectable in blood for days or even weeks in regular users — long after any impairing effect has worn off. Benzodiazepines can remain detectable for days. The presence of a drug metabolite in your blood does not mean you were impaired behind the wheel. In our experience, jurors understand that distinction once someone explains it to them clearly. Our job is to make sure someone does.

Why Drug DWI Cases Can Be Won

Because there is no automatic legal limit, the prosecution has to prove actual impairment through circumstantial evidence: an officer's roadside observations, a subjective DRE opinion, and a blood result that shows presence rather than impairment. Every piece of that case can be attacked.

• The DRE opinion. Cross-examining the officer's training, methodology, and conclusions can expose how much of the evaluation rests on judgment calls rather than science.
• The "signs of impairment." Fatigue, stress, anxiety, medical conditions, or plain nervousness during a police encounter can produce many of the same symptoms officers attribute to drugs. A strong defense shows that what the officer saw is just as consistent with explanations that have nothing to do with intoxication.
• The blood result. Forensic toxicology experts can testify about therapeutic ranges, tolerance in regular users, detection windows, and the difference between a substance being present and a driver being impaired.
• The lab work itself. Blood collection, storage, and analysis must follow strict protocols. Chain of custody gaps, improper storage temperatures, contamination risks, and laboratory errors can all compromise the reliability of the result.
• Your prescription. If you took a legally prescribed medication at the dose your doctor ordered, your prescribing physician can testify about the medication's expected effects at therapeutic doses — and about the tolerance to sedating side effects that regular patients often build over time.

The mistake we see most often is pleading guilty because the blood test came back positive, as if that settled the question. It does not. The blood test is where the fight begins, not where it ends.

If your charge is built on medication you take every day, exactly as prescribed, call our Conroe office today. Bring the prescription bottle. Your dosage history and your doctor's perspective may become the backbone of your defense, and we want them in hand before the state locks in its theory of your case.

Drug DWI Defense in Montgomery County

Montgomery County law enforcement has made drug-impaired driving a priority, with particular attention to marijuana and opioid impairment. Local agencies are training more officers in the DRE protocol, and prosecutors here are pursuing drug DWI cases more aggressively.

That local trend is exactly why local knowledge matters. At Griffin & Cain, we know how these cases are built and tried in Montgomery County courts. We cross-examine DRE officers on their methodology and credentials, challenge the scientific reliability of their conclusions, and present testimony from forensic toxicology experts and other defense experts so the jury sees the whole picture — not just the state's version of it. Our Conroe office serves clients throughout The Woodlands, Huntsville, Magnolia, and the surrounding areas.