Can You Get a DWI for Drugs in Texas? A San Antonio DWI Lawyer Explains
- Christian Vega
- May 9
- 4 min read
If you were arrested for DWI in Bexar County and no one smelled alcohol on your breath, or you had a valid prescription for everything in your system, you may be wondering how that charge is even possible. The answer is in the statute. Texas DWI law reaches far beyond alcohol. It covers any substance that causes you to lose the normal use of your mental or physical faculties, and that includes prescription medications, marijuana, and much more.
Texas DWI law applies to drugs, not just alcohol.
There is no legal limit for drugs — no "0.08 equivalent" for marijuana or prescriptions.
Having a valid, lawfully prescribed medication is not a defense under Texas law.
Police use trained Drug Recognition Experts (DREs) and blood testing to build drug DWI cases.
If you've been charged with DWI involving drugs in San Antonio, get a defense attorney involved early.
What the Law Actually Says About Drug DWI in Texas
Section 49.01(2) of the Texas Penal Code defines "intoxicated" two ways. The first is having a blood alcohol concentration (BAC) of 0.08 or higher — the number most people know. The second is 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 those substances, or any other substance into the body.
That second definition is where drug DWI cases are built. It does not require a specific number. It does not require an illegal drug. It requires proof that whatever was in your system caused you to lose the normal use of your mental or physical faculties while you were operating a motor vehicle in a public place.
This means the same DWI statute that applies to a drunk driver also applies to someone who drove after taking prescription opioids, sleeping pills, anti-anxiety medication, or marijuana. If the substance impaired your driving, Texas law treats you as intoxicated.
One more thing: Section 49.10 of the Texas Penal Code states directly that having a legal entitlement to use a substance — a valid prescription, for example — is not a defense to DWI. That language is plain. Many people do not learn it until they are sitting across from a prosecutor.
What This Means for Drivers in Bexar County
San Antonio police officers and Bexar County law enforcement are trained to identify signs of drug impairment that go well beyond what most people associate with a DWI stop. Where an alcohol DWI investigation centers largely on breath test numbers, a drug DWI investigation involves a much broader evidentiary picture.
Officers look for behavioral indicators: slow responses to questions, difficulty following instructions, slurred speech, abnormal pupil size, and poor performance on field sobriety tests. Different drug categories cause different physiological responses. CNS depressants — which include many common prescription medications like sleep aids, muscle relaxers, and opioids — can produce signs of impairment similar to alcohol but without the odor of alcohol.
Texas certifies certain officers as Drug Recognition Experts (DREs). A DRE uses a standardized 12-step evaluation — checking blood pressure, pulse, pupil size, and additional field tests — to form an opinion about which category of drugs may be causing impairment. There are seven drug categories in the DRE protocol: CNS depressants, CNS stimulants, hallucinogens, dissociative anesthetics, narcotic analgesics, inhalants, and cannabis.
If your blood is drawn following an arrest in Bexar County, it typically goes to a crime laboratory for toxicology testing. A forensic toxicologist can then testify about what substances were found and what effects those substances are documented to have on the human body.
An important distinction: a positive blood test for a drug does not automatically establish that you were intoxicated under Texas law. The State must still prove you lost the normal use of your mental or physical faculties. Blood results are significant evidence, but not the end of the analysis.
What to Do If You Are Stopped for DWI Involving Drugs in San Antonio
Knowing your rights before this happens is always better than figuring it out at the side of a road. Here is what applies under Texas law:
Stop and provide documents. Pull over safely and provide your license, registration, and proof of insurance. You are legally required to do this.
Exercise your right to remain silent. You are not required to tell the officer what medications you take, what you used earlier, or how you are feeling. Anything you say will be documented and may be used against you. This includes explaining your prescription.
Field sobriety tests are not mandatory. Standardized field sobriety tests are voluntary in Texas. There is no automatic legal penalty for declining to perform them, though the officer may note the refusal.
Understand what a chemical test refusal costs. Refusing a blood or breath test, while it may be smart, will trigger a driver's license suspension under the Administrative License Revocation (ALR) process — a separate civil proceeding from your criminal case.
Invoke your right to counsel. Once you are under arrest, ask for a lawyer and stop talking. Do not attempt to explain your medical history or convince the officer you are not impaired.
When to Call a Bexar County DWI Defense Attorney
Drug DWI cases in San Antonio are fact-intensive and involve medical and scientific evidence that needs to be examined carefully. How the stop was conducted, how blood was obtained, how the lab processed the sample, and whether the evidence actually establishes lost normal use of faculties — these are all questions worth asking with an attorney.
By Christian O. Vega, Attorney at Law | The Law Office of Christian Vega · 130 E. Travis #425, San Antonio, TX 78205
Past results do not guarantee similar outcomes in any future case. The information here is general legal information about Texas law, not legal advice for your specific situation. Reading this post does not create an attorney-client relationship.