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 Marijuana in Texas — Driving While High

You can be charged with DWI in Texas for driving under the influence of marijuana even if you have a legal prescription for medical cannabis under the Texas Compassionate Use Program. Unlike alcohol, where a BAC of 0.08 creates a per se presumption of intoxication, there is no legal THC limit in Texas. The prosecution must prove that you did not have the normal use of your mental or physical faculties due to marijuana use. This creates both challenges and opportunities for the defense.

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.

How Marijuana DWI Differs from Alcohol DWI

No Per Se THC Limit

Texas has no statute establishing a specific THC blood concentration that constitutes intoxication. This means the prosecution cannot simply point to a number on a lab report the way it can with a 0.08 BAC result. Instead, the prosecution must prove impairment through the officer’s observations, field sobriety test performance, Drug Recognition Expert (DRE) evaluations, and/or toxicology results that are inherently more ambiguous than alcohol testing.

THC Blood Levels Do Not Correlate Reliably with Impairment

Scientific research has consistently shown that THC blood concentrations do not correlate with impairment the same way BAC does with alcohol. THC is fat-soluble, meaning it is absorbed into fatty tissues and released slowly over time. A regular cannabis user may have detectable THC levels in their blood for days or weeks after last use, long after any impairing effects have dissipated. A positive THC blood test does not prove the person was impaired at the time of driving.

Drug Recognition Expert (DRE) Evaluations

When an officer suspects marijuana impairment, they may request a Drug Recognition Expert evaluation. DRE officers follow a 12-step protocol designed to identify drug-induced impairment. However, the DRE protocol is subjective. It relies on the officer’s interpretation of physical signs and symptoms, many of which can be caused by medical conditions, fatigue, anxiety, or other factors unrelated to drug use. Our attorneys challenge DRE evaluations by examining the officer’s training, the specific observations documented, and whether the conclusions are supported by the evidence.

Defense Strategies

• Challenge the traffic stop. The officer must have reasonable suspicion of a traffic violation or criminal activity to initiate the stop. If the stop was unlawful, all evidence obtained as a result is subject to suppression.
• Challenge the basis for suspecting marijuana. The smell of marijuana alone, without more, is increasingly challenged as a basis for expanded searches. Officers may claim to smell marijuana to justify further investigation, but the presence of hemp (which is legal) can produce the same odor.
• Challenge the blood test timeline. There is no retrograde extrapolation for THC values.
• Challenge the DRE evaluation. DRE protocols are subjective and officer-dependent. The scientific community has raised significant questions about DRE reliability, and our attorneys are prepared to challenge every step of the evaluation.
• Present alternative explanations. Physical signs the officer attributed to marijuana such as red eyes, elevated pulse, dry mouth and pupil dilation can be caused by allergies, contact lens wear, fatigue, anxiety, medication, or medical conditions.

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.