What Is Drug DWI (DUID) Under Texas Law?
Under Texas Penal Code §49.04, a person is intoxicated when they lack "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." There is no legal threshold for drugs the way there is a .08 BAC limit for alcohol. Impairment, not concentration, is what the state must prove. A drug DWI lawyer Houston builds every defense around this single evidentiary gap between presence and impairment.
Substances That Can Lead to DUID Charges
What Is a Drug Recognition Evaluation and How Can It Be Challenged?
A Drug Recognition Evaluation is a 12-step NHTSA-standardized protocol administered by a certified Drug Recognition Expert (DRE) — an officer trained to identify drug impairment categories without a chemical test. The DRE protocol was developed in the 1970s and produces an officer's subjective opinion about which drug category is impairing the suspect, not an objective measurement. DRE evaluations include pupil size measurement in three lighting conditions, pulse rate, blood pressure, muscle tone, and behavioral observation. Herman challenges DRE evaluations aggressively. A drug DWI lawyer Houston challenges DRE evidence as aggressively as any breath or blood test result:
DRE evaluation results are based on subjective officer interpretation. The protocol has known error rates, and studies show DREs incorrectly classify drug category in a significant percentage of cases. Herman cross-examines DRE officers on their training, methodology, and case-specific findings.
Many symptoms the DRE protocol associates with drug use have innocent explanations: fatigue, medical conditions, anxiety, contact lenses, or medication taken days ago. Herman documents alternative explanations for every observation noted in the DRE report.
Drug DUID typically requires a blood test to confirm substance presence. Herman challenges the warrant (if obtained), chain of custody, lab procedures, and the critical distinction between drug presence and actual impairment at the time of driving. A drug DWI lawyer Houston reviews every stage of the blood draw process for defects that can suppress the result entirely.
Can You Be Charged with DWI for Taking Prescription Medication in Texas?
Texas law explicitly includes "dangerous drugs" in the DWI statute, and this includes legally prescribed medications. Even if you are taking medication exactly as prescribed by a doctor, you can be charged with DWI if those medications impair your normal faculties. Herman identifies and documents your prescription history, dosage, and medical condition to contextualize the evidence the state will present. A drug DWI lawyer Houston uses prescription and medical history as core evidence, not a footnote.
Drug DWI cases almost always involve a blood draw. See how Herman challenges blood test evidence in Texas DWI cases. The 15-day ALR deadline to contest your license suspension applies to drug DWI arrests exactly as it does to alcohol cases. A drug DWI lawyer Houston handles the ALR fight and the criminal defense together from the first phone call. This page covers drug and DUID-specific defenses; for the full Texas DWI process that applies alongside them, see the Houston DWI lawyer overview and the Harris County DWI page. If your arrest specifically involved a legally prescribed medication — opioids, benzodiazepines, sleep aids, or muscle relaxants — see the dedicated prescription drug DWI page for the tolerance and therapeutic-dose defenses specific to prescription medication cases.
Page last reviewed for accuracy against current Texas Penal Code and Texas hemp law provisions: August 2026.
How Does an Opioid or Fentanyl-Related DWI Differ From Other Drug DWI Cases?
Opioid-related DUID arrests present a unique defense profile because so many defendants are taking the medication under a valid, current prescription for a legitimate medical condition. Officers frequently misread ordinary side effects — drowsiness, slowed speech, slight unsteadiness — as impairment, when those same symptoms may simply reflect a patient's baseline on a stable, long-term dosage. Tolerance is a critical factor the DRE protocol does not account for: a patient who has taken the same opioid dose for months functions very differently than someone taking it for the first time, yet a DRE evaluation treats both cases identically. Fentanyl cases carry additional urgency because trace amounts can appear in blood tests from lawful medical treatment, including hospital procedures, and the state must still connect a specific blood concentration to impairment at the moment of driving. A drug DWI lawyer Houston builds these prescription-tolerance and medical-history defenses specifically for opioid and fentanyl DUID cases, where the gap between chemical presence and genuine impairment is often widest.
Can Legal Hemp, Delta-8, or CBD Products Still Lead to a DWI Charge?
Texas's 2019 hemp law legalized products with 0.3% or less delta-9 THC by dry weight, which is why delta-8 THC, CBD oils, and other hemp-derived products are sold openly in Houston. That legal status does not extend to driving: the same "no per se limit, impairment is what matters" rule covered above applies just as fully to delta-8 and CBD as it does to marijuana or any controlled substance. A blood test showing THC metabolites does not distinguish between marijuana, legal delta-8, or a CBD product that was cross-contaminated with THC during manufacturing — a real and documented problem in an industry with inconsistent lab testing standards. A drug DWI lawyer Houston clients rely on for these cases obtains the product's certificate of analysis where available and uses it to show the client had no reason to believe a legal hemp product would trigger any impairment or any positive test at all.
Drug DWI Defense Questions
No. Unlike alcohol's .08 per se limit, there is no legal THC concentration threshold in Texas. The state must prove you were actually impaired at the time of driving. THC metabolites can remain in blood for days or weeks after use without causing impairment. Herman's defense specifically challenges whether the THC level detected correlates with impairment at the relevant time, not just recent use. A drug DWI lawyer Houston can request lab retesting to separate recent use from lingering metabolites.
You can refuse, but officers will typically seek a warrant for a blood draw in suspected drug DWI cases. A warrant-authorized blood draw is legally compelled, and refusal at that point can lead to additional legal problems. The blood evidence itself can often be challenged — Herman's focus is on suppression motions and lab result challenges, not the refusal itself.
Yes. Texas DWI law covers all substances that impair normal mental or physical faculties — including legally prescribed medications. Even taking medication exactly as directed by your doctor can result in a DWI charge if an officer believes your driving was impaired. Herman builds a defense around your prescription history, dosage, duration of use, and expert testimony about how the medication affects driving ability versus the officer's lay observations.
A DRE is an officer trained in a 12-step evaluation protocol to identify drug impairment categories. The protocol includes pulse rate checks, pupil measurement in different light conditions, muscle tone assessment, and observation of vital signs. Herman cross-examines DRE officers on their training records, calibration of instruments used, case-specific findings, and the known error rates of the DRE protocol — which studies show misclassifies drug category in a significant percentage of evaluations.
Without a per se limit, the state relies on: (1) officer observations of driving behavior and field sobriety test performance, (2) DRE evaluation results, and (3) blood or urine test results showing substance presence. Herman challenges each component — the reliability of officer observations, the validity of the DRE protocol, and the lab procedures for the chemical test. Proving impairment without a legal threshold is harder for the state than an alcohol case, and Herman exploits that evidentiary gap. A drug DWI lawyer Houston exploits exactly this evidentiary gap in every DUID case.
The penalties for DUID are identical to alcohol DWI — a first offense is a Class B misdemeanor with a minimum 72 hours in jail, up to 180 days, and a fine up to $2,000 plus surcharges. A second DUID is a Class A misdemeanor; a third is a felony. If you also possessed a controlled substance, you face a separate drug possession charge layered on top of the DWI. Herman addresses both the DUID charge and any accompanying possession charge simultaneously.
Yes — marijuana DUID cases are among the most defensible drug DWI cases because there is no per se impairment threshold and because THC metabolites persist in blood long after any actual impairment. Herman challenges the temporal link between the positive blood test result and the time of driving, presents alternative explanations for driving behavior, and cross-examines officer observations. Many marijuana DUID cases result in dismissal when challenged by an experienced DWI attorney. A drug DWI lawyer Houston sees marijuana DUID cases dismissed more often than almost any other DWI charge type.
Yes — the ALR license suspension process applies to all DWI charges, including DUID. You have 15 days from arrest to request an ALR hearing to contest the suspension. Failing to request the hearing results in automatic suspension 40 days after the arrest date. Herman files the ALR hearing request immediately upon being retained and defends both the criminal case and the administrative license action simultaneously.
Multiple substances complicate the state's case in some ways — each substance must be shown to have contributed to impairment, and the combined effect argument requires toxicological expert testimony. Herman retains independent toxicology experts in polydrug DWI cases to challenge the state's expert on the specific impairment profile of each detected substance, the absence of correlation between blood levels and driving impairment, and any alternative causes for the driving behavior observed. A drug DWI lawyer Houston retains the same caliber of toxicology experts the state itself relies on.
Yes — and Herman does this routinely in DUID cases. Blood draw challenges include: whether a valid warrant was obtained; whether the phlebotomist was properly licensed; whether the sample was properly preserved with anticoagulant and preservative; whether the chain of custody was maintained; and whether the lab followed required testing protocols. A procedural defect in any of these steps can result in suppression of the blood test result, often leading to dismissal of the entire case. A drug DWI lawyer Houston walks through every one of these procedural steps before deciding on a defense strategy.
Yes. Legal hemp status under Texas's 2019 hemp law does not protect against a DWI charge — impairment is what matters, not whether the product was legal to purchase. A standard blood test also cannot distinguish delta-8 or CBD-derived THC metabolites from marijuana, and cross-contamination in unregulated hemp products is common. Herman uses the product's certificate of analysis, purchase records, and dosage history to challenge whether a legal product could plausibly have caused impairment.