Lewisville DUID Lawyers

A drug DWI in Texas is still a DWI. There is no separate “DUID” statute. Texas Penal Code § 49.04 covers alcohol, drugs, and everything in between. But drug DWI cases operate differently at the forensic and investigative level than alcohol cases. There is no per se drug limit the way there is a 0.08 BAC. The state relies on blood toxicology, Drug Recognition Evaluations, and circumstantial evidence to prove impairment. And because many drugs produce metabolites that linger long after the psychoactive effects have ended, the gap between what the lab report says and what actually happened on the road is often larger than the state’s case suggests.

DUID charges arising in Lewisville are prosecuted by the Denton County District Attorney’s Office at the Denton County Courthouse, 1450 E. McKinney Street, Denton, TX 76209. Many Lewisville-area DUID arrests originate from traffic stops on I-35E, SH-121 (Sam Rayburn Tollway), FM-3040, and the western terminus of the President George Bush Turnpike.

Deandra Grant Law has defended DUID charges in Denton County for more than 30 years. Managing Partner Deandra Grant is a trained SFST instructor and holds the ACS-CHAL Forensic Lawyer-Scientist designation along with a Master of Science in Pharmaceutical Science and a Graduate Certificate in Forensic Toxicology. Partner Douglas Huff holds the same ACS-CHAL designation.

Drug DWI in Texas — Penal Code § 49.04 and § 49.01

Under Penal Code § 49.04(a), a person commits DWI if the person is intoxicated while operating a motor vehicle in a public place. “Intoxicated” is defined in § 49.01(2):

• (A) 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; or
• (B) Having an alcohol concentration of 0.08 or more.

The (B) per se prong applies only to alcohol. There is no per se drug concentration in Texas DWI law. Every drug DWI case requires the state to prove actual impairment under the (A) prong.

The State’s Impairment Burden — And Why It Is Contestable

In an alcohol DWI case with a 0.08 BAC result, the state can secure a conviction on the per se prong regardless of how the defendant behaved or performed on field sobriety tests. In a drug DWI case, there is no per se shortcut. The state must establish:

• That the defendant was not in normal use of mental or physical faculties at the time of driving;
• That the loss of normal use was caused by a drug, controlled substance, dangerous drug, or other substance (not by fatigue, medical condition, or other factors);
• That the substance was in fact present in the defendant’s system at impairing concentrations at the time of driving.

Each of these elements is contestable. A driver who was fatigued, had a medical episode, or was under stress may exhibit impairment signs without drug involvement. Even where a drug is detected, whether it was present at impairing concentrations (and whether it in fact caused the observed impairment) is rarely as clear-cut as the state presents it.

Common DUID Substance Categories

Marijuana and THC

The most-prosecuted DUID category in North Texas. Several structural features of cannabis pharmacology make these cases particularly defensible:

• No per se THC threshold. Texas has no statutory cutoff for THC blood concentration. A number standing alone cannot prove impairment.
• THC is lipid-soluble and persists long after impairment ends. Active THC can remain detectable in blood for days to weeks in regular users, far beyond the typical 3-to-4-hour impairment window after consumption.
• THC metabolites (11-nor-9-carboxy-THC, or “carboxy-THC”) are not psychoactive. Lab results often report carboxy-THC alongside active THC. A positive carboxy-THC result alone indicates past use, not current impairment.
• Hemp-derived products with trace THC. Legal hemp products containing less than 0.3% Δ9-THC can contribute to blood THC readings in the low nanogram range without causing impairment.

Prescription Medications

Opioids (hydrocodone, oxycodone, tramadol), benzodiazepines (alprazolam, diazepam, clonazepam), sleep aids (zolpidem, eszopiclone), ADHD medications, and various SSRI/SNRI antidepressants all appear in DUID cases. The critical legal point:

• A valid prescription is not a defense under §49.10. Penal Code §49.10 expressly bars the fact of a valid prescription from serving as a defense to a DUID charge. Even a patient taking a medication exactly as prescribed can be convicted of DUID if the state proves loss of faculties caused by that medication.
• “Took as directed” is relevant to mitigation, not to guilt. Prescription compliance does not defeat the charge, but it may affect how the DA’s office approaches resolution and how a jury views culpability.
• Polypharmacy interaction. Combinations of prescribed medications (often prescribed by different doctors with no cross-awareness) can produce impairment that none of the individual medications would cause. This is a genuine defense complication and a jury-comprehensible narrative in appropriate cases.

Controlled Substances

Methamphetamine, cocaine, heroin, MDMA, and other Penalty Group substances appear in DUID cases. Special defense considerations:

• Methamphetamine: d-meth vs l-meth. Standard immunoassay screens do not distinguish illegal d-methamphetamine from l-methamphetamine, the active ingredient in legal OTC products such as Vicks inhalers. Only LC-MS/MS confirmatory testing with chiral separation distinguishes the two. A positive methamphetamine screen alone does not establish illegal methamphetamine use.
• Cocaine metabolites. Benzoylecgonine (a cocaine metabolite) can persist long after cocaine itself is cleared. A positive benzoylecgonine result alone indicates past exposure, not current impairment.

Polydrug Cases

Combinations of alcohol with controlled substances, or multiple controlled substances together, are common in DUID cases. The statute permits prosecution based on “a combination of two or more of those substances,” which gives the state flexibility but also creates forensic challenges. Quantifying the contribution of each substance to observed impairment is scientifically difficult, and the state’s expert testimony on combined-substance impairment is frequently contestable.