Texas's intoxication definition reaches beyond alcohol: it covers the loss of normal use of mental or physical faculties from any substance — including lawfully prescribed medication taken as directed. Drivers are arrested for DWI on painkillers, anxiety medications, sleep aids, muscle relaxants, and combinations with a single glass of wine.
A valid prescription is not a defense
The statute doesn't care whether the substance was legal for you to possess — only whether it impaired you behind the wheel. "My doctor prescribed it" explains the situation; it doesn't answer the charge. Ambien-type sleep medications are a recurring example, including cases where drivers insist they have no memory of driving at all.
How the state builds these cases
Without alcohol, there's no BAC shortcut. Officers lean on driving behavior, performance on field sobriety tests, a Drug Recognition Expert (DRE) evaluation, and a blood draw analyzed for the medication and its metabolites. Each link has known weaknesses: DRE opinions are subjective, lab detection of a substance is not proof of impairment at the time of driving, and therapeutic blood levels don't map neatly onto impairment the way alcohol levels claim to.
Where the defense lives
Medication cases are fought on pharmacology and procedure: whether the blood level was within the prescribed therapeutic range, whether the timing of the dose matches the timing of driving, whether the DRE followed the 12-step protocol, and whether a medical condition explains the observed "impairment" better than the drug. Medical records and prescribing history become central evidence — gather them early.
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