A marijuana DWI in Texas carries the same penalties as an alcohol DWI under Penal Code § 49.04, but the case the state has to build looks different. There is no per se THC limit in Texas, no roadside breathalyzer for marijuana, and no clean number for a prosecutor to put in front of a jury.
That changes the evidence the case turns on. Officers lean on field sobriety tests designed for alcohol, observations of behavior, and drug recognition expert evaluations that are far more subjective than a BAC reading. A positive THC blood result often reflects use days or weeks earlier, a fact most jurors don’t know unless someone in the courtroom explains it.
RJ Harber is a former prosecutor who has handled marijuana- and drug-related DWI cases across Texas for more than 15 years. If you’ve been charged with a DWI involving marijuana, contact us today for a free consultation.
Marijuana DWI Under Texas Law
Texas Penal Code §49.04 makes it an offense to operate a motor vehicle in a public place while intoxicated. The statute does not separate marijuana DWI from alcohol DWI as different offenses.
A person is considered intoxicated either by losing the use of mental or physical skills because of alcohol, a controlled substance, a drug, or another substance, such as marijuana.
Since there is no per se THC limit in Texas, section 49.10 forecloses an entitlement defense in marijuana cases: even if the defendant is or was authorized to use the substance—by prescription, medical use, or otherwise—that authorization is not a defense to DWI.
THC Levels and Impairment Under Texas DWI Law
Alcohol DWI gives the prosecution a number: 0.08 or higher; marijuana has no equivalent. A blood test that comes back positive for THC does not, by itself, establish DWI.
The state still has to prove loss of normal use at the time the driver was operating the vehicle. THC can stay detectable in blood and urine for days after use, so a positive result tells the jury the driver had used marijuana, not when or whether the driver was impaired behind the wheel.
Implied Consent and Mandatory Blood Draws in Texas
A driver can refuse a voluntary specimen request, but refusal carries consequences. Under §724.015, the officer must give written notice that refusal can be used at trial and that the driver’s license will be automatically suspended for at least 180 days.
Refusal does not end the inquiry in every case. The law requires the officer to take a specimen even on refusal in certain situations, including a collision with bodily injury, probable death of a victim, hospital transport, or a DWI-with-child-passenger arrest. Outside those scenarios, §724.012(e) bars a forced specimen without a warrant or without probable cause and exigent circumstances.
Penalties for Cannabis DWI Charges
1st DWI offense
- A fine of up to $2,000
- Between 3 and 180 days in jail
- License suspension for up to a year
- A separate $3,000 fine under Texas Transportation Code §709.001, payable on conviction
2nd DWI offense
- A fine of up to $4,000
- Between 1 month and 1 year in jail
- A separate $4,500 fine under Texas Transportation Code §709.001, payable on conviction, if the second conviction falls within a 36-month window of the first
3rd DWI offense
- A $10,000 fine
- Between 2 and 10 years in prison
- A separate $4,500 fine under Texas Transportation Code §709.001, payable on conviction, if the conviction falls within a 36-month window of a prior DWI
Aggravating Factors in Marijuana DWI Cases
Child Passenger Under 15: Texas Penal Code §49.045 makes it a state jail felony to operate a motor vehicle while intoxicated with a passenger younger than 15. The §12.35 range is 180 days to 2 years in state jail, with a fine of up to $10,000.
Accident Causing Bodily Injury or Death: A marijuana DWI that causes serious bodily injury becomes an intoxication assault under §49.07, a third-degree felony at baseline.
Accident Causing Death: If the collision causes a death, the charge becomes intoxication manslaughter under §49.08, a second-degree felony with a §12.33 range of 2 to 20 years.
School Crossing Zone: A marijuana DWI can be elevated to a state jail felony if the offense occurred in a school crossing zone while the reduced speed limit applies. The enhancement is location-specific and time-specific.
Defenses to a Marijuana DWI Charge
Officer Observations and Field Sobriety Tests: Officers usually start with observations on driving behavior, the smell of marijuana, red eyes, slow speech, and admissions at the stop. They then move to the standard field sobriety battery. However, those tests were validated for alcohol impairment. HGN does not reliably indicate marijuana use, since cannabis does not typically produce horizontal nystagmus. Which might be grounds for the defense.
Drug Recognition Expert Evaluations: When roadside testing leaves the officer uncertain, agencies often call in a Drug Recognition Expert. The DRE protocol is a 12-step evaluation in which the officer forms an opinion about which drug category caused impairment, then closes with a toxicological examination—a chemical test meant to support the opinion. The protocol is widely used in Texas, but not infallible. DRE conclusions rest on the officer’s training and judgment rather than chemical confirmation, and the methodology is open to challenge on cross-examination.
Probable Cause for a Stop: The state has to establish reasonable suspicion for the stop and probable cause for the arrest. If this cannot be established from the beginning, the whole case may be dismissed.
Problematic Test Results: Whether the blood draw was supported by a valid warrant, whether the chain of custody was intact, and whether the testing lab followed accepted methods round out the procedural challenges available to the defense.
Contact a Dallas Marijuana Attorney
A marijuana DWI charge in Texas turns on evidence that is contestable at every step, from the stop through the blood draw to the ALR hearing. Attorney RJ Harber has handled marijuana and drug DWI-related cases throughout Dallas. We work to challenge the impairment evidence, protect the license, and seek the best possible outcome. Contact a Dallas marijuana lawyer today for a free consultation.
Frequently Asked Questions
When can a police officer make a marijuana DWI arrest in Dallas?
The arresting officer needs probable cause that the driver was operating a vehicle while impaired by observable signs of impairment from driving conduct, field sobriety performance, and statements at the scene. Because marijuana doesn’t have a per se threshold like alcohol’s 0.08, the officer’s observations and any blood test results carry weight. That’s why DWI cases involving marijuana tend to be very fact-specific.
Can I be charged with both DWI and marijuana possession from the same arrest?
Yes. These are separate offenses under Texas law, and a single traffic stop can result in both. If the officer finds illegal amounts of marijuana in the vehicle, prosecutors can file a drug possession charge under the Texas Controlled Substances Act in addition to the DWI. Each count carries its own penalties, so a conviction on both can mean stacked criminal charges on your record.
What happens to my driver’s license after a marijuana DWI arrest?
You have 15 days from receipt of the suspension notice to request an ALR hearing—miss that deadline and your driver’s license is suspended automatically.
Why do I need a lawyer to defend me against a marijuana DWI charge?
Given the strict Texas laws in criminalizing marijuana, it is critical that you hire an experienced lawyer. Your lawyer will be able to critically analyze all aspects of your case, review the facts, investigate your case, and skillfully apply relevant state and federal laws.