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The Polypharmacy Problem

Many drug DWI arrests involve multiple substances (ex. an antidepressant combined with a benzodiazepine; marijuana combined with alcohol; opioid medication combined with muscle relaxants). When the state’s blood testing reveals multiple substances, the causation analysis becomes significantly more difficult:

• Which substance caused which observed effect?
• Were any of the substances present at impairment-level concentrations?
• Did interactions between substances produce effects that neither would have caused alone?
• Was the driver’s impairment caused by one specific substance, a combination, or neither?

The state bears the burden of proving impairment “by reason of” the drug (meaning specific causation). In polypharmacy cases, that burden is often hard to meet.

Drug Recognition Expert (DRE) Evidence and Its Limits

Many drug DWI arrests in Collin County involve a Drug Recognition Expert which is a police officer trained in a 12-step drug evaluation protocol developed by the International Association of Chiefs of Police. The DRE testifies at trial as an “expert” about the category of drug present and the impairment observed.

The DRE protocol includes breath alcohol testing, interview with the arresting officer, preliminary examination and first pulse, eye examinations (HGN, Lack of Convergence, VGN), divided attention psychophysical tests, vital signs and second pulse, dark room examinations, muscle tone, injection sites and third pulse, subject statements, opinion of the evaluator, and toxicological examination.

Key defense issues with DRE evidence:

• The 12-step protocol is subject to substantial operator error and subjective interpretation.
• Research on DRE accuracy has shown error rates ranging roughly 30–56% across various drug categories in validation studies.
• The DRE is trained to identify seven drug categories, not specific drugs. The identification is based on physiological observations, not chemistry.
• DRE testimony is often admitted without a Daubert-style reliability hearing, despite known accuracy limits.
• Cross-examination on the specific steps, the protocol’s empirical basis, and the officer’s training and experience is central to challenging DRE testimony.

Forensic Defense — LC-MS/MS and Screening vs Confirmation

Drug identification in Texas DUID cases generally proceeds in two stages: a screening test (typically immunoassay) followed by a confirmatory test (typically liquid chromatography-tandem mass spectrometry, or LC-MS/MS). McKinney-area DUID blood specimens are typically submitted to the DPS Crime Lab in Garland. The distinction between screening and confirmation matters:

• Immunoassay screens produce false positives. Cross-reactivity with legal substances is well documented. A positive screen alone is not a reliable basis for a DUID conviction.
• LC-MS/MS confirmation is the gold standard. But LC-MS/MS has its own methodological requirements (calibration, internal standards, matrix effects, quantification limits) that are all contestable. Measurement uncertainty at low concentrations is often substantial.
• Chain of custody. Every transfer of the blood sample from collection through analysis must be documented without interruption. Breaks in chain of custody create grounds to challenge identification of the sample.
• ACS-CHAL-level review. As Texas’s first ACS-CHAL Forensic Lawyer-Scientist, Deandra Grant reads the underlying laboratory packet — chromatograms, calibration curves, quality control data, method validation — not just the summary report. Douglas Huff holds the same ACS-CHAL credential.

Defense Strategies in Collin County DUID Cases

Challenging the loss-of-faculties element. Because there is no per se threshold, the state must prove loss of normal mental or physical faculties. Video of the stop, field sobriety performance, speech and coordination observations, and driving behavior are all relevant and all contestable. Conduct consistent with normal faculties despite drug presence is the core reasonable-doubt narrative in appropriate cases.

Separating presence from impairment. Drug presence in blood proves only that the drug was used at some point in the detection window. For substances with long detection windows (THC, benzodiazepines, long-acting opioids), presence does not equal current impairment. This is a jury-comprehensible distinction that matters.

SFST limitations on DUID cases. Standard Field Sobriety Tests are validated for alcohol impairment detection. Their reliability for drug impairment detection is materially weaker. HGN, in particular, is not reliable for many drug categories. As a trained SFST instructor, Deandra Grant addresses these limitations in every DUID case.

Forensic and methodological challenges. Calibration, chain of custody, screening vs confirmation methodology, measurement uncertainty, and analyst qualifications are all contestable at the chemistry level.

Article 38.23 — no good faith exception. Stops, field sobriety investigations, arrests, and blood warrants are all subject to constitutional review. Texas’s exclusionary rule carries no good faith exception so evidence from an unlawful stop or search is suppressible regardless of what it shows.

ALR as discovery. Requesting the ALR hearing produces sworn officer testimony and early discovery that shapes the criminal defense strategy. The ALR deadline is 15 days from the date of notice of suspension.

Why Deandra Grant Law for McKinney DUID Defense

• • Office in Allen — minutes from McKinney. 30+ years in Collin County courts. 500+ trials to verdict. The Collin County Courthouse is in McKinney itself, and the Collin County DA’s office is familiar ground.
  • Trained SFST Instructor — Deandra Grant. Field sobriety test administration, scoring, and interpretation challenged in every case — including the limitations of SFSTs for drug impairment detection.
  • ACS-CHAL Forensic Lawyer-Scientist — Deandra Grant and Douglas Huff. LC-MS/MS methodology, immunoassay cross-reactivity, chain of custody, and the State’s forensic evidence evaluated at the chemistry level.
  • Master of Science in Pharmaceutical Science + Graduate Certificate in Forensic Toxicology. Drug metabolism, detection windows, dose-response relationships, and the pharmacology of impairment — credentials that matter more in DUID cases than in standard alcohol DWIs.
  • Article 38.23 — no good faith exception. Every DUID case begins with the lawfulness of the stop, search, or seizure.
  • Federal defense capability. James Lee Bright handles federal cases in the Eastern District of Texas (Sherman Division).
  • 17 published law books. Including The Texas DWI Manual
  • Texas Super Lawyer since 2011. 

• AV® Preeminent rated by Martindale-Hubbell®.

If you are facing DUID or drug-related DWI charges in Collin County, call (214) 225-7117 for a free, confidential consultation. Or schedule online at texasdwisite.com.