Under Texas Penal Code Section 49.04, a person commits the offense of driving while intoxicated if they operate a motor vehicle in a public place while intoxicated. Texas defines intoxication as either having a blood alcohol concentration of 0.08 or higher or not having the normal use of mental or physical faculties due to the introduction of alcohol, a controlled substance, a drug, a dangerous drug, a combination of substances, or any other substance into the body.

That final clause is doing a lot of legal work. It means any substance — including a lawfully prescribed medication — can form the basis of a DWI charge if an officer believes it impaired your ability to drive.

Which Prescription Medications Most Often Are Linked to DWI Charges Due to Impairment?

Several legal prescription drugs can impair driving ability and commonly appear in Texas DWI arrests, including opioids, benzodiazepines, sleep aids, and muscle relaxers.

Knowing which medications raise red flags can help you understand why you were stopped and what the prosecution may argue. The categories below appear frequently in prescription drug DWI cases across Texas.

Opioid Pain Relievers

Medications like hydrocodone, oxycodone, codeine, and tramadol are prescribed regularly for pain management. They can cause drowsiness, slowed reaction time, and impaired judgment — all of which affect driving. Officers are trained to look for small, constricted pupils, slowed speech, and droopy eyelids as potential indicators of opioid use, though these signs alone are not conclusive proof of driving impairment.

Benzodiazepines

Drugs like Xanax (alprazolam), Valium (diazepam), Klonopin (clonazepam), and Ativan (lorazepam) are prescribed for anxiety, panic disorders, and seizures. They slow the central nervous system. Behind the wheel, that translates to poor coordination, delayed response, and difficulty tracking moving objects — all behaviors a Drug Recognition Expert (DRE) officer is trained to identify.

Sleep Medications

Zolpidem (Ambien) is one of the more commonly cited drugs in Texas DWI cases involving sleep aids. According to official FDA warnings [insert direct link/citation to FDA safety communication for authority], residual impairment can persist into the following morning, meaning a person who took the medication as prescribed the night before may still face impairment — and an arrest — the next day.

Muscle Relaxers

Medications such as cyclobenzaprine (Flexeril) and carisoprodol (Soma) are prescribed for muscle spasms and pain. They cause sedation and cognitive slowing that can significantly affect a driver’s ability to respond to traffic conditions.

Stimulants and ADHD Medications

Though stimulants like Adderall and Ritalin work differently from the drugs above, they carry their own risks. At certain doses or when combined with other substances, they can cause agitation, irregular heart rate, and tunnel vision that affects driving.

How Do Police Detect Prescription Drug Impairment?

Officers use roadside observations, field sobriety tests, and Drug Recognition Experts to build a DWI case when alcohol is absent but impairment is suspected.

Standard breath tests do not detect prescription drugs. When an officer suspects a driver is impaired by something other than alcohol, they may call in a certified Drug Recognition Expert. A DRE follows a 12-step evaluation process that examines eye responses, vital signs, muscle tone, and other indicators to identify a category of drug. Their opinion can be submitted as evidence in court.

Blood draws are also common in these cases. Texas law allows officers to obtain a warrant for a blood sample if you refuse, and while the results may show the presence and concentration of prescription medications in your system, a blood result alone does not automatically prove a DWI without independent evidence of actual impairment.

Does Having a Valid Prescription Help Your Case?

A valid prescription is not a legal defense to DWI in Texas, but it is relevant context that a skilled defense attorney can use strategically.

The existence of a lawful prescription tells the court you were not using a substance illegally — but it does not establish that you were unimpaired. What it does do is open the door to arguments about dosage, physician instruction, and whether the observed behavior was truly consistent with impairment. That nuance matters in front of a jury.

What to Do If You Were Arrested for a Prescription Drug DWI?

Do not assume this charge will resolve itself because your medication was legal. Texas prosecutors pursue these cases aggressively, and the consequences of a conviction — including license suspension, fines, and a permanent criminal record —are broadly the same as a first-offense alcohol-related DWI, though exact penalties can vary based on prior offenses and specific aggravating factors.

The most important step you can take is to speak with a defense attorney before you say anything further to law enforcement or accept any plea offers. Evidence in prescription drug DWI cases can be challenged on multiple grounds, from the reliability of the DRE evaluation to the handling and testing of your blood sample.

Talk to Shane Phelps Law About Your Case

At Shane Phelps Law, we understand how disorienting it feels to face criminal charges for taking medication your doctor prescribed. Our team represents clients in Bryan and throughout the surrounding area, and we approach every case with the same attention and dedication we would want for ourselves or our families. If you are facing a prescription drug DWI, call us at 979-596-6843 or contact us to discuss your situation. What you share with us stays confidential.