Can You Get a DWI for Prescription Medication in San Antonio? What Texas Law Actually Says

You take your medication exactly as your doctor prescribed. You’re not drinking. You’re driving home from work, running an errand, or picking up your kids. Then you see the flashing lights in your rearview mirror. A few minutes later, you’re handcuffed, your car is being towed, and you’re facing a DWI charge—even though you didn’t touch a drop of alcohol.

This scenario happens more often than many San Antonio residents realize. And when it does, the shock is overwhelming. How can Texas charge you with a DWI when you were taking legal medication? It can. But a charge is not a conviction, and a prescription medication case is often far more fightable than people think. If you’re facing a prescription medication DWI in Bexar County, here’s what you need to know about Texas law, what the prosecution must prove, and how these cases are defended.

Texas Law Doesn’t Care That the Medication Was Prescribed

Under Texas law, a person is considered intoxicated if they lack the normal use of mental or physical faculties due to the introduction of alcohol, a controlled substance, a drug, a dangerous drug, or any other substance into the body.

Notice what’s missing from that definition: there is no requirement that the substance be illegal. The Texas Court of Criminal Appeals has consistently held that a valid prescription does not exempt a driver from prosecution if the medication caused intoxication. The law is built around public safety—an impaired driver is a danger regardless of the source of the impairment. This means even if you took your medication exactly as prescribed by a licensed physician, you can still be arrested, prosecuted, and punished the same way as any other DWI defendant.

Which Prescription Medications Are Most Commonly Involved?

Several categories of prescription medication appear repeatedly in Texas DWI prosecutions. While millions of people take these medications and drive safely every day, each has documented effects that the state may use to argue impairment.

• Sleep aids like Ambien, Lunesta, and Sonata have FDA warnings about morning-after impairment, and “sleep driving”—driving without conscious memory—is a documented adverse effect.
• Benzodiazepines like Xanax, Valium, Ativan, and Klonopin can cause drowsiness, impaired coordination, slowed reaction time, and cognitive impairment.
• Opioid pain medications like Vicodin, Norco, OxyContin, and Percocet can cause sedation, slowed reaction time, and impaired judgment.
• Muscle relaxers like Flexeril and Soma can cause significant sedation and slowed reaction time.
• Antihistamines like Benadryl and Vistaril can cause significant sedation, particularly in older adults.
• Some antidepressants and ADHD medications can affect cognition and behavior in ways the state may argue produced impairment.

This list is illustrative, not exhaustive. The point is that prescription DWI is not an exotic charge—it reaches across the most commonly prescribed drug classes in American medicine.

What the Prosecution Has to Prove

In a prescription DWI case, the state must establish three elements.

• Operation of a motor vehicle in a public place. This means driving on a road, highway, or in a parking lot open to the public.
• Loss of normal use of mental or physical faculties. This is proven through driving behavior, officer observations, statements, field sobriety test performance, and witness testimony.
• Loss of faculties caused by the introduction of a substance. This is proven through chemical evidence, typically blood toxicology, the defendant’s own statements, or prescription records.

Notice what the state does not have to prove: a quantitative threshold of the medication in the blood. Texas has no per-se drug limit. The state has to prove the substance was present and that it caused loss of faculties—not that it reached a particular concentration.

This both helps and hurts defendants. It hurts because there is no safe level the defense can point to. It helps because the state has to do the harder work of connecting presence to impairment—and that connection is forensically contestable.

How Police Build Their Case

The Traffic Stop and Observations

A prescription DWI case often starts with ordinary facts that officers turn into an impairment narrative. Driving behavior like weaving, drifting, or delayed reactions can come from fatigue, distraction, pain, or stress—not just intoxication.

Once an officer decides you’re impaired, every detail gets filtered through that decision. Slow answers become delayed mental processing. Nervousness becomes confusion. A driver with pain, fatigue, or anxiety becomes unsteady.

Field Sobriety Tests

Police rely heavily on field sobriety tests because they create observations the officer can describe later. But these tests were built around alcohol detection, not medication effects. They were not designed to measure every medication effect, medical condition, or physical limitation.

If you were tired, injured, anxious, older, recovering from surgery, or taking medication that affects balance or speech, your performance may say very little about intoxication.

Drug Recognition Experts

Sometimes the state calls in a Drug Recognition Expert, an officer with additional training who performs a twelve-step evaluation. The DRE’s conclusion is still an opinion from law enforcement about whether you lost the normal use of your faculties.

Here’s the problem: DREs are not medical doctors or pharmacologists. The DRE protocol was created by police officers, not scientists. Peer-reviewed research has called the accuracy of the entire DRE protocol into question. Even the DRE training manual states that the drug influence evaluation isn’t an exact science and that DREs are not infallible.

Courts across the country have refused to allow DREs to present their opinions as evidence at trial. In Texas, a judge can prevent a DRE from giving an expert opinion if the court believes the protocol is unsupported by scientific studies.

Chemical Testing

Blood testing is the state’s primary tool in prescription medication cases. But a positive test result shows the drug was present—it does not automatically show you lost normal use of your faculties. Presence does not equal impairment.

Realistic Penalties in Bexar County

Prescription DWI penalties are the same as alcohol-related DWI offenses.

• A first offense is a Class B misdemeanor with three to one hundred eighty days in jail, a fine up to two thousand dollars, and license suspension of ninety days to one year.
• A second offense is a Class A misdemeanor with thirty days to one year in jail, a fine up to four thousand dollars, and license suspension of six months to two years.
• A third offense is a third-degree felony with two to ten years in prison, a fine up to ten thousand dollars, and license suspension of six months to two years.

Beyond these penalties, a conviction creates a permanent criminal record that can affect employment, professional licenses, housing, and insurance rates.

Common Defenses in Prescription DWI Cases

• The stop was unlawful. If the officer lacked reasonable suspicion to stop your vehicle, any evidence obtained during the stop may be inadmissible.
• The officer’s observations are wrong. Body camera and dashcam footage can show that what the officer called impairment actually had innocent explanations.
• Field sobriety tests were improperly conducted. Poor conditions like uneven ground, traffic, lighting, or weather, improper footwear, or bad instructions can invalidate test results.
• Medical conditions explain the symptoms. Fatigue, anxiety, neurological issues, vertigo, or other conditions can mimic intoxication symptoms.
• The DRE evaluation is flawed. The DRE protocol has documented reliability problems and can be challenged on cross-examination.
• The blood test is flawed. Method validation, calibration, analyst qualifications, and chain of custody are all defensible issues.
• Presence of medication doesn’t mean impairment. This is the central question in every prescription DWI case: can the state prove actual impairment, not just the presence of a drug?

What to Do If You’re Charged

In the First Twenty-Four Hours

• Exercise your right to remain silent. You are not required to answer questions about what prescription medications you have taken.
• Request an attorney immediately. Do not try to talk your way out of it.
• Remember the fifteen-day deadline. After a DWI arrest, you have only fifteen days to request an ALR hearing or your license will be automatically suspended.

Records to Preserve

• Prescription labels and dosage instructions
• Pharmacy records
• Doctor’s notes
• A timeline of when you took each dose

These details can connect the timing, dosage, and your condition to what officers observed.

The Bottom Line

Texas law does not distinguish between illegal drugs and legally prescribed medication when it comes to DWI charges. If a medication affects your ability to drive, you can be arrested and prosecuted. But a prescription DWI case is not the same as an alcohol DWI case. There’s no per-se limit to point to. The state has to prove actual impairment—and that connection is often built on subjective opinions that can be challenged.

If you’re facing a prescription DWI charge in San Antonio, Bexar County, or anywhere in Texas, the fight is usually not over whether medication was present. The real fight is whether the officer was right about impairment. And that’s a fight you can win with the right defense.

Frequently Asked Questions

1. Can I really get a DWI in Texas for taking my prescription medication exactly as prescribed?

Yes. Under Texas law, a DWI can be based on impairment from any substance, including legally prescribed medication. The law does not require the substance to be illegal—it focuses on whether you lost the normal use of your mental or physical faculties while driving.

2. Does having a valid prescription protect me from a DWI charge?

No. A valid prescription explains why the medication is in your system, but it does not prevent an arrest or prosecution if the state alleges the medication caused impairment. The Texas Court of Criminal Appeals has consistently held that a prescription is not a defense to DWI.

3. How do officers determine if prescription medication is impairing me?

Officers look at driving behavior, physical signs like slurred speech, balance issues, and slow responses, field sobriety test performance, and statements you make. They may also use a Drug Recognition Expert for a twelve-step evaluation, or request a blood test. However, these methods are subjective and can be challenged in court.

4. What are the penalties for a prescription medication DWI in Texas?

Penalties are the same as for alcohol-related DWI. A first offense is a Class B misdemeanor with up to one hundred eighty days in jail, a two thousand dollar fine, and license suspension of up to one year. A second offense is a Class A misdemeanor with up to one year in jail and a four thousand dollar fine. A third offense is a third-degree felony with two to ten years in prison and a ten thousand dollar fine.

5. What is a Drug Recognition Expert and are they reliable?

A Drug Recognition Expert is a police officer with additional training who performs a twelve-step evaluation to determine whether a person is under the influence of drugs. However, DREs are not medical doctors or pharmacologists, and the protocol was created by police, not scientists. Peer-reviewed research has called the accuracy of the DRE protocol into question, and courts across the country have refused to allow DRE testimony.

6. If my blood test shows the medication, does that prove I’m guilty?

No. A positive blood test shows the drug was present—it does not automatically show you lost normal use of your faculties. Presence does not equal impairment. The state must prove the connection between the drug and actual impairment, which is forensically contestable.

7. What should I do if I’m arrested for a prescription DWI?

Exercise your right to remain silent—you are not required to answer questions about your medications. Request an attorney immediately. And remember: you have only fifteen days to request an ALR hearing after a DWI arrest, or your license will be automatically suspended.