Most DWI cases I handle involve alcohol. But I also see cases where the client was completely sober — no alcohol whatsoever — and still got arrested for driving while intoxicated. If that sounds impossible, it isn’t. Texas law has two separate definitions of “intoxicated,” and only one of them requires alcohol. The other covers drugs, prescription medications, controlled substances, and essentially anything else that can affect how your brain and body function.
If you’ve been charged with DWI and your breath test came back clean — or you weren’t given one — that doesn’t mean the case disappears. It means the fight looks different. The penalties are the same as a standard alcohol DWI — including the risk of a permanent conviction, license suspension, and jail time. What changes is how the State tries to prove it, and where the defense lives.
The Two Definitions of “Intoxicated” Under Texas Law
Under §49.01(2) of the Texas Penal Code, “intoxicated” means one of two things. Both definitions can support a DWI conviction. Only one of them involves alcohol.
Not having the normal use of mental or physical faculties by reason of the introduction of alcohol, a controlled substance, a drug, a dangerous drug, a combination of two or more of those substances, or any other substance into the body. This is the prong drug DWI cases are charged under.
Having an alcohol concentration of 0.08 or more. This is the “per se” standard most people are familiar with — if your BAC is at or above 0.08, you’re legally intoxicated regardless of how you appear or perform on field sobriety tests.
Drug DWI cases live entirely under Prong A. The State doesn’t need a number — they need to prove that some substance caused you to lose the normal use of your mental or physical faculties. “Any other substance” is deliberately broad language. It covers prescription drugs, over-the-counter medications, herbal supplements, and substances the legislature didn’t specifically name. If a police officer believes a substance — whatever it is — impaired your driving, that’s enough to make an arrest.
What Substances Can Trigger a DWI Charge
Marijuana
Marijuana is the most common substance in the non-alcohol DWI cases I see. Texas has not legalized recreational marijuana, and a valid medical prescription doesn’t protect you from a DWI charge. What makes marijuana cases particularly complicated is the detection window — THC metabolites can show up in a blood test weeks after the last use, long after any actual impairment has passed. A positive blood test for THC does not prove you were impaired while you were driving. That distinction is critical, and it’s where the defense often lives in marijuana DWI cases.
Prescription Medications
Benzodiazepines like Xanax and Klonopin, opioids like Hydrocodone and Oxycodone, sleep aids, muscle relaxers, and certain antidepressants can all form the basis of a drug DWI charge. The fact that your doctor prescribed the medication is not a defense — more on that below. If the State can argue the drug caused you to lose normal use of your faculties while driving, the prescription doesn’t change the charge.
Illicit Drugs
Cocaine, methamphetamine, heroin, and other controlled substances can all support a DWI charge under Prong A. These cases tend to involve more aggressive prosecution, and the presence of the substance in a blood draw often comes packaged with additional drug possession charges.
Combinations
The statute explicitly covers “a combination of two or more” substances. Someone who had two drinks — well below 0.08 — combined with a prescribed sedative could still be charged under Prong A if the combination caused impaired driving. The State doesn’t need either substance alone to hit a threshold. The combination itself is enough.
Fatigue, Medical Conditions, and Mistaken Arrests
Police are trained to spot signs of intoxication — slurred speech, glassy eyes, unsteady balance, slow reactions. They are not trained to rule out other causes of those same signs before making an arrest. Diabetic episodes, seizure disorders, severe fatigue, anxiety attacks, and other medical conditions can look almost identical to drug intoxication to an untrained officer. I’ve seen clients arrested for DWI who had no substance in their system at all — just a medical event the officer didn’t recognize.
Having a Prescription Is Not a Defense
This is the part that shocks most people. Under §49.10 of the Texas Penal Code, the fact that you were legally entitled to use the substance — that your doctor prescribed it, that you filled it at a pharmacy, that you took it exactly as directed — is explicitly not a defense to a DWI charge.
Texas Penal Code §49.10 states directly that a defendant’s legal entitlement to use a substance is not a defense to DWI. Taking your prescribed Xanax or Hydrocodone exactly as your doctor instructed does not insulate you from prosecution if the State can argue the medication impaired your driving. The only question the law cares about is whether the substance caused you to lose normal use of your mental or physical faculties — not whether you had permission to take it.
This doesn’t mean these cases are unwinnable. It means the defense strategy shifts. Instead of arguing “I had a prescription,” we focus on whether the substance actually caused impairment at the level the statute requires — and whether the State can actually prove that beyond a reasonable doubt.
The DRE Problem — Why Drug DWI Cases Are Hard to Prove
Here’s where these cases get interesting from a defense standpoint.
The three standard field sobriety tests — the Horizontal Gaze Nystagmus (HGN), the walk-and-turn, and the one-leg-stand — were studied, designed, and validated by the National Highway Traffic Safety Administration specifically to detect alcohol impairment. They were built around how alcohol affects the human body. They were not designed to detect impairment from marijuana, opioids, benzodiazepines, or any other substance.
There is a formal training program — Drug Recognition Expert (DRE) certification, offered through the International Association of Chiefs of Police — that trains officers to evaluate drug impairment using a 12-step protocol. It’s a significant investment of time and training, and the reality is that very few patrol officers in Collin County are certified DREs. When the arresting officer in your case isn’t a DRE, they’re applying alcohol-based evaluation tools to a drug case — and their ability to offer an expert opinion on drug impairment at trial is something I’m going to challenge.
The second problem is that there’s no legal limit for drugs the way there is for alcohol. The State can’t just point to a number and say “that’s over the limit.” They have to prove — through officer testimony, blood test results, and often a forensic toxicologist — that the substance actually caused impairment while you were driving. That’s a harder case to build than a 0.08 breath test, and it’s a harder case for the State to sell to a jury.
How I Defend Drug DWI Cases
Drug DWI cases require a different approach than alcohol DWI cases. The defense points are different, the evidence is different, and the experts matter more. Here’s where I look first.
Detection Is Not Impairment
A positive blood test tells you a substance was present in someone’s system. It does not tell you whether that person was impaired while they were driving. This is especially true with marijuana, where THC metabolites persist in blood for days or weeks after any impairment has passed. I push hard on what the test actually proves — and what it doesn’t.
The Officer’s Qualifications
If the arresting officer isn’t a certified DRE, I’ll challenge whether they’re qualified to offer an expert opinion on drug impairment. Performing a walk-and-turn test and deciding someone is “on something” is not the same as a trained, systematic evaluation. An officer who isn’t qualified to render that opinion shouldn’t be permitted to offer one at trial.
The Field Sobriety Tests
The standard tests were not validated for drug impairment. If the State is relying on HGN, walk-and-turn, or one-leg-stand as evidence of drug intoxication, I’ll address the foundation of that evidence — what those tests were actually designed to measure, and why a “failure” on an alcohol test doesn’t prove drug impairment.
Blood Test Challenges
The chain of custody for a blood draw, the qualifications of the analyst, the testing methodology, and what the actual results mean in terms of impairment are all areas I examine carefully. A toxicologist testifying that a certain concentration of a substance was found is not the same as a toxicologist testifying that concentration caused impairment. Those are two different claims, and I’ll hold the State to proving the right one.
Alternative Explanations
Medical conditions, severe fatigue, anxiety, and other factors can produce signs that look like drug intoxication to an officer who wasn’t trained to distinguish them. If there’s a legitimate alternative explanation for what the officer observed, I’ll build that into the defense.
Frequently Asked Questions About Drug DWI in Texas
Can I get a DWI for marijuana even if I’m not high anymore?
Yes — you can be arrested and charged based on a positive blood test even if you haven’t smoked in days or weeks. THC metabolites stay in your system long after any impairment is gone. Whether that charge results in a conviction is a different question. The State still has to prove you were actually impaired while you were driving, not just that marijuana was detectable in your blood. That’s a meaningful distinction, and it’s one of the primary defense angles in marijuana DWI cases.
My doctor prescribed the medication. How can I be charged with DWI?
Because the Texas Penal Code says the prescription doesn’t matter. §49.10 explicitly makes your legal entitlement to use the substance irrelevant to whether you committed DWI. The only question is whether the substance caused you to lose normal use of your mental or physical faculties while driving. Taking your medication exactly as prescribed is not a defense — but it doesn’t mean the case is unwinnable. It means the fight is over whether the State can actually prove impairment.
Is there a legal limit for drugs in a DWI case like the 0.08 BAC for alcohol?
No. Texas has no per se drug limit — no threshold concentration for any substance that automatically equals DWI the way 0.08 does for alcohol. The State has to prove impairment through officer observations, test results, and expert testimony. That’s both harder to prosecute and harder to defend against, because there’s no bright line. It means the outcome depends heavily on the specific evidence in your case.
What’s a Drug Recognition Expert, and does it matter if the officer wasn’t one?
A Drug Recognition Expert (DRE) is a police officer who has completed a formal certification program specifically designed to identify drug impairment. The standard field sobriety tests that most officers use were designed to detect alcohol impairment — not drug impairment. If the officer who arrested you isn’t a certified DRE, their ability to offer an expert opinion on whether you were impaired by drugs is something I’ll challenge. It’s one of the most significant defense issues in drug DWI cases.
Can a medical condition or fatigue cause a false DWI arrest?
Yes. Diabetic episodes, seizures, anxiety attacks, stroke symptoms, severe fatigue, and other medical conditions can produce signs — slurred speech, unsteady gait, slow reactions, glassy eyes — that look like intoxication to an officer who wasn’t trained to rule out other causes. Police are trained to identify signs of intoxication. They’re not trained to diagnose medical conditions or eliminate other explanations before making an arrest. If a medical condition was involved in your arrest, that matters to your defense.
What should I do if I was charged with DWI but hadn’t been drinking?
Don’t try to explain yourself to the police — anything you say about what you took, when you took it, or how you felt will be used against you. These cases require a defense attorney who has actually handled drug DWI cases, because the strategy is different from an alcohol DWI and the evidence issues are different. I’ve handled these cases in Collin County, and I know where the State’s case is typically weakest. Call me and we’ll talk through what happened — free consultation, no obligation.
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