A prescription is not a defense, and that surprises people
Under Texas law you can be charged with DWI while taking medication exactly as prescribed. The question is not whether the drug was legal. The question is whether you lost the normal use of your mental or physical faculties. Sleep aids, muscle relaxers, anti-anxiety medication, and pain medication all show up in these cases in Orange County.
That is a harsh rule and juries do not always like it. It is also an opening, because the State still has to prove impairment at the time of driving, not just presence of a substance.
Why drug DWI cases are weaker than they look
In an alcohol case the State has a number and a well established relationship between that number and impairment. In a drug case it has neither.
- Blood tests detect metabolites that can remain long after any effect has ended. THC-COOH is the clearest example. Its presence says you used, not when.
- Standard field sobriety tests were developed and validated for alcohol. Their accuracy for other substances is far less established.
- A Drug Recognition Expert evaluation is a twelve step protocol producing an opinion, not a measurement. Whether the officer followed all twelve steps is checkable.
- Polypharmacy cases, where two or more substances are present, produce interaction claims that frequently go beyond what the toxicology can actually support.
I look at whether the DRE was current on certification, whether the rolling log was maintained, whether the opinion was formed before or after the toxicology came back, and whether the lab quantified anything or only reported presence.
The toxicology itself
Drug panels run on LC-MS/MS or GC-MS rather than the headspace GC used for alcohol. Different instrument, same principle: it is a measurement with a method behind it, and the method has validation records, calibrators, controls, and limits of detection and quantitation.
A result reported near the limit of quantitation carries far more uncertainty than the single number on the report suggests. That uncertainty rarely makes it into the State's presentation unless somebody puts it there.
See also: alcohol DWI defense in Orange.
Questions people ask
Can I be charged with DWI for legally prescribed medication?
Yes. Texas law does not carve out prescriptions. The State must still prove you lost the normal use of your faculties, which is where these cases are won and lost.
How long does marijuana stay in a blood test?
Active THC clears relatively fast, often within hours. The inactive metabolite can be detected for days or weeks in regular users. If the State's evidence is metabolite only, it is evidence of past use, not of impairment behind the wheel.
What is a DRE and does it hold up?
A Drug Recognition Expert is an officer trained in a twelve step evaluation protocol. It produces an opinion about drug category. It holds up better when every step was documented and worse when the officer skipped steps or knew the toxicology first.