Last verified: April 2026
The Legal Framework
Driving while intoxicated in Texas is governed by Penal Code §49.04, which makes it an offense to operate a motor vehicle in a public place while intoxicated. The definition of "intoxicated" under §49.01 includes two pathways:
- 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 two or more of those substances, or any other substance into the body
- Having an alcohol concentration of 0.08 or more
For cannabis, there is no equivalent of the 0.08 BAC threshold. Prosecution relies entirely on the first definition — proving that the driver did not have "normal use" of their faculties due to cannabis consumption. This makes cannabis DWI cases more subjective and more dependent on officer testimony than alcohol DWI cases.
"Intoxicated" means: (A) 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 two or more of those substances, or any other substance into the body; or (B) having an alcohol concentration of 0.08 or more.
Texas Penal Code §49.01(2)
DWI Penalties
Cannabis DWI penalties follow the same escalation structure as alcohol DWI:
| Offense | Classification | Jail/Prison | Fine | License Suspension |
|---|---|---|---|---|
| 1st DWI | Class B misdemeanor | 3–180 days | Up to $2,000 | 90 days–1 year |
| 2nd DWI | Class A misdemeanor | 30 days–1 year | Up to $4,000 | 180 days–2 years |
| 3rd DWI | Third-degree felony | 2–10 years prison | Up to $10,000 | 180 days–2 years |
| DWI with child passenger | State jail felony | 180 days–2 years | Up to $10,000 | 90 days–2 years |
A first-offense DWI also carries a mandatory $3,000–$6,000 surcharge (Driver Responsibility Program fee) and typically requires completion of a DWI education program. Enhanced penalties apply if the driver's BAC was 0.15 or higher, if there was an accident causing injury (intoxication assault) or death (intoxication manslaughter), or if a child under 15 was in the vehicle.
No Per Se THC Limit
Unlike alcohol, where a blood alcohol concentration of 0.08 creates automatic legal intoxication, Texas has no per se THC limit. There is no nanogram threshold at which a driver is legally presumed to be impaired by cannabis. This is actually the majority position among U.S. states, though some states (Colorado, Washington, Montana, Ohio, Nevada) have adopted 5 ng/mL limits.
The absence of a per se limit cuts both ways. On one hand, a driver cannot be convicted based on a blood test alone. On the other, it means there is no "safe" level — any detectable THC could support a DWI charge if the officer and prosecutor argue impairment.
There is no scientifically demonstrated correlation between a specific level of THC in blood or oral fluid and driving impairment. Per se limits for THC are arbitrary and unsupported by science.
AAA Foundation for Traffic Safety, "An Evaluation of Data from Drivers Arrested for Driving Under the Influence" (2016)
The Drug Recognition Expert (DRE) Program
Because there is no chemical test for cannabis impairment comparable to the breathalyzer for alcohol, Texas relies heavily on the Drug Recognition Expert (DRE) program to build cannabis DWI cases. DREs are officers who complete 152 hours of specialized training and follow a 12-step evaluation protocol to assess suspected drug impairment.
The 12-step protocol includes breath alcohol testing, eye examinations (horizontal gaze nystagmus, vertical gaze nystagmus, lack of convergence), divided attention tests, vital signs measurement, pupil size assessment, muscle tone checks, and a toxicological examination. Based on the evaluation, the DRE renders an opinion on whether the person is impaired and by what category of drug.
DRE testimony is scientifically contested. Studies have found that DREs correctly identify cannabis impairment at varying rates, and the protocol's reliability has been challenged in courts across the country. Defense attorneys routinely argue that DRE evaluations are subjective, that the science does not support the claimed accuracy rates, and that DRE officers have an inherent confirmation bias.
Blood Draws and Consent
Implied Consent
Under Transportation Code §724.011, a person who operates a motor vehicle on Texas roads is deemed to have given consent to a chemical test (breath or blood) to determine intoxication. However, this implied consent is not absolute. A driver may refuse a blood draw, but refusal triggers an automatic 180-day driver's license suspension (2 years for repeat refusals).
Mandatory Blood Draws
Under Transportation Code §724.012(b), officers may obtain a blood draw without consent in specific circumstances:
- Any crash involving serious bodily injury or death
- The driver has a prior DWI conviction (any number)
- A child under 15 is in the vehicle
- The driver has a prior conviction for intoxication assault or manslaughter
Warrantless Blood Draws
The U.S. Supreme Court's decision in Missouri v. McNeely (2013) and the Texas Court of Criminal Appeals' decision in State v. Villarreal (2014) established that warrantless, nonconsensual blood draws are generally unconstitutional under the Fourth Amendment. The natural dissipation of THC in the bloodstream does not, by itself, create an exigent circumstance justifying a warrantless draw. Officers must typically obtain a warrant from a magistrate before drawing blood over a driver's objection.
"No Refusal" Programs
Many Texas jurisdictions run "No Refusal" programs during holidays and high-traffic weekends (Memorial Day, July 4th, Labor Day, New Year's Eve). During these programs, on-call judges or magistrates are available to issue electronic blood draw warrants within minutes of a driver's refusal. The practical effect is that refusing a blood test does not prevent testing — it merely adds a brief delay while officers obtain a warrant.
Prosecution Challenges with Cannabis DWI
Cannabis DWI cases present unique challenges for prosecutors:
- THC metabolites persist in blood for days or weeks after the psychoactive effects have worn off, meaning a positive blood test does not prove impairment at the time of driving
- No dose-response correlation — unlike alcohol, there is no established relationship between a specific blood THC level and a specific degree of impairment
- Tolerance varies widely — regular cannabis users may show high THC blood levels while exhibiting minimal impairment
- Field sobriety tests were designed and validated for alcohol impairment and may not reliably detect cannabis impairment
These challenges do not mean that cannabis DWI charges cannot result in convictions. Officers' observations of driving behavior, field sobriety performance, physical signs (red eyes, odor, delayed responses), and DRE evaluations can all be presented as evidence. But convictions are harder to secure than in alcohol DWI cases, and experienced defense attorneys can effectively challenge the evidence.