New! AI Legal Avatar — Get 24/7 Answers on Texas DWI Law, Penalties, and Defenses

Our AI Legal Avatar provides instant, plain-language answers to your questions about Texas DWI laws—like penalties, license suspension, and defense strategies—anytime, day or night. While it's a helpful starting point, it doesn't replace the clarity and advocacy of our experienced DWI attorneys.

DWI Prescription Drugs in Texas

Many Texans are surprised to learn that they can be charged with DWI for driving under the influence of medication that was legally prescribed to them by their doctor. Under Texas Penal Code §49.01, intoxication includes not having the normal use of mental or physical faculties by reason of the introduction of “a drug, a dangerous drug, a combination of two or more of those substances, or any other substance into the body.” Having a valid prescription is not a defense to DWI in Texas.

An entire chapter in Deandra’s book, The Texas DWI Manual, is devoted to drugged driving defense. In addition, Deandra has a Master’s Degree in Pharmaceutical Science.

Common Prescription Drugs That Lead to DWI Charges

• Benzodiazepines (Xanax, Valium, Klonopin, Ativan) — prescribed for anxiety, panic disorders, and insomnia. Can cause drowsiness, slowed reaction time, impaired coordination, and confusion.
• Opioid pain medications (hydrocodone, oxycodone, morphine, fentanyl patches) — can cause drowsiness, dizziness, slowed reflexes, and impaired judgment
• Sleep medications (Ambien, Lunesta, trazodone) — designed to induce sleep, and residual effects can impair driving the next morning
• Muscle relaxants (Soma, Flexeril, Robaxin) — cause drowsiness and impaired coordination
• Antihistamines (diphenhydramine/Benadryl, hydroxyzine) — cause significant drowsiness in many users
• ADHD medications (Adderall, Ritalin) — when taken in doses higher than prescribed or combined with other substances
• Antidepressants and antipsychotics — some cause drowsiness, blurred vision, or impaired coordination

Why Prescription Drug DWI Cases Are Different

No Per Se Standard

Unlike alcohol DWI, there is no concentration level of any prescription drug that automatically establishes intoxication in Texas. The prosecution must prove that the drug caused you to lose the normal use of your mental or physical faculties which is a subjective standard that depends on the officer’s observations, your performance on field sobriety tests, and toxicology results.

Therapeutic vs. Impairing Levels

A blood test showing the presence of a prescription drug does not prove impairment. Most prescription drugs have a therapeutic range which is a concentration range at which the drug provides its intended medical benefit without causing impairment. If your blood concentration is within the therapeutic range prescribed by your doctor, you may not have been impaired even though the drug was present in your system.

Drug Tolerance

Patients who take prescription medications regularly develop tolerance to the sedating or impairing side effects over time. A dose that would impair a first-time user may have no impairing effect on a long-term patient. The prosecution often fails to account for this tolerance when arguing impairment.

Defense Strategies

• Challenge the officer’s basis for suspecting drug impairment. Officers are trained primarily in alcohol detection. Their observations of “impairment” may actually reflect your medical condition, fatigue, or anxiety rather than drug effects.
• Challenge the DRE evaluation. Drug Recognition Expert protocols have known limitations and are subject to officer subjectivity. The signs attributed to drug impairment often overlap with symptoms of medical conditions or normal variations in physical presentation.
• Present therapeutic use evidence. Your prescribing physician can testify about the medication’s intended effects at your prescribed dose and whether impairment would be expected.
• Challenge the toxicology results. Blood tests may detect the presence of a drug without establishing an impairing concentration. Our forensic training allows us to evaluate whether the detected levels are consistent with therapeutic use or with impairment.
• Raise the “involuntary intoxication” defense. If you were not warned by your doctor or pharmacist that the medication could impair driving, you may argue a lack of knowledge of the impairing effects.

Defend Your DWI Case with Science — Contact Deandra Grant Law

If you are facing DWI charges in Texas, contact Deandra Grant Law for a free, confidential consultation. Our attorneys hold ACS-CHAL Forensic Lawyer-Scientist designations and Deandra has a Master’s Degree in Pharmaceutical Science which gives us the scientific training to challenge the prosecution’s evidence at a level most defense attorneys cannot match. Lead attorney Deandra Grant has defended thousands of DWI cases over 30+ years.