Not Only Alcohol
Drug DWI and Prescription Medication
A Texas DWI does not require alcohol. The definition of intoxicated covers a controlled substance, a drug, a dangerous drug, or any combination of substances.
That includes medication prescribed to you. Section 49.10 states plainly that being entitled to use the substance is not a defense.
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Two ways to be intoxicated, and only one involves a number
Section 49.01(2) defines intoxicated two independent ways. The first is not having the normal use of mental or physical faculties by reason of a substance. The second is an alcohol concentration of 0.08 or more.
A drug case runs entirely on the first theory. There is no equivalent of the 0.08 line for medication, no threshold concentration to exceed, and no chemical shortcut for the State. It has to prove loss of normal faculties.
That cuts both ways. It removes the number that makes an alcohol case look objective, and it puts the officer's observations and the video at the center of the case. What loss of normal use looks like, and whether the recorded behavior actually shows it, becomes the whole argument.
Section 49.11 removes any culpable mental state requirement, so not realizing the medication would affect you is not a defense either. But there is a difference between not intending an effect and not having one.
The broader Texas intoxication guide explains how this loss-of-faculties theory fits beside alcohol concentration, operation, and public-place elements.
Where drug DWI cases are contested
Evaluating drug-intoxication evidence
A drug recognition evaluation records an officer's observations and conclusions; it does not create a statutory concentration threshold for drugs. The report should be compared with the complete video, the instructions actually given, the person's medical history, and documented conditions that may affect speech, balance, eye appearance, coordination, or alertness. The legal question remains whether the State can prove loss of normal mental or physical faculties under section 49.01(2).
Toxicology must also be read in context. The identified substance and metabolites, prescribed dose, refill history, time of the last dose, collection time, reported concentration, and any combination of substances can bear on the analysis. A prescription is not a defense under section 49.10, but prescription and timing evidence can still help evaluate whether the substance caused the alleged loss of faculties when the vehicle was operated.
A blood test shows presence, not impairment
Many substances remain detectable long after any effect has passed. A positive result establishes that something was in your system, which is not the same as establishing loss of normal faculties at the time of driving.
Roadside tests were built for alcohol
The standardized battery was developed and validated against alcohol impairment. Applying the same scoring to a suspected drug case imports assumptions that were never tested for it.
Medical conditions look like impairment
Neurological conditions, injuries, fatigue and the underlying condition the medication treats can each produce what an officer describes as impairment.
Related pages
Drug DWI questions
I had a valid prescription. Is that a defense?
No. Section 49.10 states that entitlement to use the substance is not a defense. What matters is whether you had the normal use of your mental and physical faculties.
Is there a legal limit for drugs like the 0.08 for alcohol?
No. There is no threshold concentration for medication or controlled substances. The State has to prove loss of normal faculties, which is why these cases turn heavily on observation and video.
A blood test found the drug in my system. Does that prove impairment?
Not by itself. Many substances stay detectable well after any effect has worn off. Presence and impairment at the time of driving are different questions.
What if I did not know the medication would affect me?
Section 49.11 removes any culpable mental state requirement, so intention is not the issue. Whether you actually lost the normal use of your faculties still is.