A Texas DWI does not have to involve alcohol.
Under Texas law, a person may be accused of driving while intoxicated when alcohol, a controlled substance, a drug, a dangerous drug, a combination of substances, or another substance allegedly causes the loss of normal mental or physical abilities while operating a motor vehicle in a public place. Texas Penal Code §§ 49.01 and 49.04 establish the basic definitions and elements of DWI.
That means marijuana, THC, prescription medications, cocaine, methamphetamine, opioids, fentanyl, and other substances can become part of a Texas DWI case.
For drivers, this can make a traffic stop involving drugs much more complicated. Police may investigate whether a substance was illegally possessed while also looking for evidence that the driver was impaired. In some cases, the same traffic stop may result in both a DWI allegation and a separate drug charge.
Those allegations need to be examined separately.
If you have been arrested or are under investigation for a drug-related DWI anywhere in Texas, Dr. Lloyd A. Newton can review the traffic stop, vehicle search, officer observations, video evidence, blood testing, toxicology, and any related drug possession allegations.
Why Can a Drug Traffic Stop Turn Into a DWI Investigation?
An officer who encounters suspected drugs during a traffic stop may be dealing with several different questions.
What is the substance?
Was it legally possessed?
Who possessed it?
Was it consumed?
When was it consumed?
Did it affect the driver’s mental or physical abilities?
Those questions are not always answered at the roadside.
Consider a traffic stop involving a THC vape cartridge. Laboratory testing may eventually be needed to determine exactly what the cartridge contains. At the same time, the officer may be making observations about the driver’s speech, balance, coordination, eyes, driving behavior, responses to questions, or performance on field sobriety tests.
The possession investigation and the DWI investigation can therefore develop along separate paths.
This distinction has become especially important with THC products. Laboratory testing of cannabis products and biological specimens continues to evolve. Texas DPS issued updated guidance concerning cannabinoid toxicology testing in 2026 and confirmed that blood is its preferred specimen when drugs are suspected in a DWI investigation.
A person should not assume that uncertainty about the legality or contents of a product automatically prevents police from pursuing a DWI allegation.
At the same time, the presence of a drug does not automatically prove that the driver was intoxicated.
What Does Texas Law Mean by “Intoxicated”?
Texas Penal Code § 49.01 provides two basic ways a person may be considered intoxicated.
One is having an alcohol concentration of 0.08 or more.
The other is not having the normal use of mental or physical faculties because of alcohol, a controlled substance, a drug, a dangerous drug, a combination of two or more of those substances, or another substance.
That second definition is especially important in drug-related DWI cases.
There is no requirement that alcohol be involved. Police and prosecutors may attempt to prove intoxication based on marijuana, THC, prescription medication, illegal drugs, or a combination of substances.
But the prosecution still has to prove the required elements of the DWI charge. Simply showing that a substance was present is not necessarily the same as proving that the substance caused the loss of normal mental or physical abilities.
What Does the Prosecution Have to Prove in a Texas Drug DWI Case?
Under Texas Penal Code § 49.04, the prosecution generally must prove that the accused:
- Operated a motor vehicle
- In a public place
- While intoxicated
In a drug-related case based on loss of normal faculties, an important question may be whether the evidence establishes that the alleged impairment resulted from the introduction of a drug or other substance into the body.
The evidence used to make that argument may include officer observations, video, driving behavior, field sobriety testing, statements, blood toxicology results, prescription medications, drugs allegedly found in the vehicle, or a Drug Recognition Expert evaluation.
A defense should examine how those pieces of evidence fit together and whether they actually support the prosecution’s theory.
Is a Drug DWI Different From a Drug Possession Charge?
Yes.
Drug possession and drug-related DWI involve different legal questions.
| Drug Possession | Drug-Related DWI |
|---|---|
| Focuses on whether a person knowingly possessed or controlled a prohibited substance | Focuses on whether a person was intoxicated while operating a motor vehicle in a public place |
| Identity and classification of the substance may determine the charge | Evidence of impairment and its connection to a substance may be central |
| Quantity may affect the offense level | Quantity possessed does not necessarily establish impairment |
| Actual or constructive possession may be disputed | Officer observations, toxicology, and driving behavior may be disputed |
| Testing may identify the substance found | Blood testing may identify substances present in the body |
| Search and seizure issues may determine whether evidence can be used | The traffic stop, detention, arrest, blood draw, and vehicle search may all need review |
A driver can potentially face both allegations from the same incident.
For example, an officer may claim that a THC vape found in the center console was possessed by the driver and also claim that the driver was impaired by THC.
Neither allegation automatically proves the other.
Can You Get a DWI for Marijuana or THC in Texas?
Yes. Texas DWI law can apply when marijuana or THC allegedly causes a driver to lose the normal use of mental or physical abilities.
But a THC DWI does not work the same way as an alcohol DWI.
Texas law does not currently establish a THC concentration that automatically equals intoxication in the way an alcohol concentration of 0.08 does.
That distinction matters.
Research reviewed by the National Highway Traffic Safety Administration has found that THC concentration in blood does not correlate with impairment in the same predictable manner as alcohol concentration. NHTSA has reported that people can show different degrees of impairment at similar THC concentrations and that blood THC levels alone are not a reliable measure of driving impairment.
As a result, a THC-related DWI case may depend heavily on the complete circumstances surrounding the stop.
Those circumstances can include:
- How the vehicle was being driven
- The reason for the traffic stop
- When THC was allegedly consumed
- How it was consumed
- Officer observations
- Body camera and dash camera footage
- Field sobriety testing
- Statements made by the driver
- When blood was collected
- The substances detected in the blood
- Other medications or substances present
- Whether the observed behavior has another explanation
A positive THC result is evidence that deserves careful review. It is not the same thing as a 0.08 alcohol result.
Does THC in Your Blood Prove You Were Impaired?
Not by itself.
THC behaves differently in the body than alcohol. NHTSA has documented that THC levels can decline rapidly after consumption and that the relationship between the concentration found in blood and actual impairment is poor. The timing of a blood draw can therefore be particularly important.
Someone’s THC level when blood is eventually collected may not neatly show how that person was functioning when the vehicle was being driven.
The defense may need to examine:
- When driving occurred
- When the traffic stop occurred
- When THC was allegedly consumed
- The form of THC allegedly consumed
- When the blood sample was collected
- What cannabinoids or metabolites were detected
- The concentration reported
- Laboratory methods
- Officer observations
- Video of the driver
- Other possible explanations for the officer’s observations
The scientific evidence should be considered along with the rest of the case rather than treated as an automatic answer to the question of impairment.
What If the THC Product Was Purchased Legally?
The legality of possessing a product and the question of impaired driving are separate issues.
A driver may have purchased a hemp-derived product, cannabis product, prescription product, or other substance from a store or authorized provider. Whether possession was legal may depend on the substance, concentration, product, labeling, testing, and other facts.
That does not automatically answer the DWI question.
A legally possessed substance may still become part of a DWI allegation if police claim it caused the driver to lose the normal use of mental or physical faculties.
The opposite distinction is also important. Finding a THC product in a vehicle does not automatically establish that the driver consumed it or that it caused impairment.
When marijuana, hemp, THC concentrates, vape cartridges, or other cannabis products are involved, both the product itself and the alleged impairment should be examined carefully.
Can Prescription Medication Cause a DWI in Texas?
Yes.
A valid prescription does not automatically prevent a Texas DWI allegation.
Texas law defines intoxication broadly enough to include a “drug” or “dangerous drug.” The question in a DWI case can therefore be whether medication caused the loss of normal mental or physical abilities, not simply whether the person was legally allowed to possess the medication.
Drug-related DWI investigations can involve medications such as:
- Xanax
- Hydrocodone
- Oxycodone
- Codeine
- Prescription sleep medications
- Certain anxiety medications
- Some pain medications
- Other medications that may affect alertness, coordination, reaction time, or judgment
The circumstances matter.
A defense may examine what medication was taken, the prescribed dose, when it was taken, whether other substances were involved, the driver’s medical condition, the officer’s observations, and whether the evidence actually demonstrates impairment.
Being prescribed a medication and being intoxicated are not the same factual question.
What If Alcohol and Drugs Were Both Involved?
Texas law also allows intoxication to be based on a combination of substances.
For example, a DWI investigation might involve allegations concerning:
- Alcohol and THC
- Alcohol and prescription medication
- Alcohol and cocaine
- Alcohol and opioids
- Multiple prescription medications
- More than one controlled substance
In these cases, prosecutors may argue that the substances worked together to cause impairment.
The defense should examine the evidence supporting that conclusion, including toxicology, timing, dosage when known, officer observations, and whether other explanations exist for the behavior described by police.
What Evidence May Police Use in a Drug-Related DWI Case?
Drug DWI cases can involve much more than a laboratory report.
Police and prosecutors may rely on evidence such as:
- Driving behavior before the stop
- The reason the vehicle was stopped
- Body camera footage
- Dash camera footage
- Statements by the driver
- Speech
- Balance and coordination
- Eye appearance or pupil observations
- Field sobriety testing
- Drugs or medications found in the vehicle
- Vape cartridges or cannabis products
- Prescription bottles
- Drug paraphernalia
- Blood testing
- Toxicology reports
- A Drug Recognition Expert evaluation
- Witness testimony
- Medical information when lawfully obtained
Each piece of evidence should be viewed in context.
Video, for example, may support an officer’s written description of impairment, or it may show something different.
A toxicology report may identify a substance, but additional analysis may be needed to determine what the result does and does not establish about impairment.
What Is a Drug Recognition Expert?
A Drug Recognition Expert, commonly called a DRE, is a law enforcement officer who has received specialized training in recognizing possible drug impairment.
The Drug Evaluation and Classification program uses a structured 12-step evaluation. According to NHTSA, the process is intended to help a DRE assess whether a person appears impaired, whether the impairment may be related to drugs or a medical condition, and what category of drug may be involved.
A DRE evaluation may involve observations of physical signs, divided-attention testing, vital signs, eye examinations, muscle tone, interviews, and toxicological testing.
A DRE’s conclusion is still evidence that can be examined and challenged. NHTSA has acknowledged that research concerning a DRE’s ability to correctly classify the drug involved has produced mixed results and that accuracy can depend on factors such as experience, drug category, and the presence of multiple substances.
The report, training, procedures followed, body camera footage, toxicology findings, and other evidence may all be relevant when evaluating a DRE opinion.
How Does Blood Testing Work in a Drug DWI Case?
Blood testing can play a major role when drugs are suspected.
Texas DPS states that blood is the preferred specimen for DWI investigations when drug testing is required. DPS explains that blood provides a better connection to the time of the suspected offense than urine, which can reflect past drug use without necessarily indicating current impairment.
The DPS Toxicology Section analyzes biological specimens in DWI investigations. Its testing may include an initial screening for classes of drugs followed by confirmation testing designed to identify specific substances. DPS states that confirmation may use gas chromatography mass spectrometry or liquid chromatography mass spectrometry, and blood concentrations may be determined for interpretive purposes.
A defense attorney may examine questions such as:
- Was the blood collected lawfully?
- Was a warrant required and, if so, was it valid?
- When was the blood collected?
- Who collected it?
- Was the sample properly labeled and stored?
- Was chain of custody maintained?
- What testing methods were used?
- What substances were actually identified?
- Were metabolites detected?
- What concentrations were reported?
- What does the laboratory result establish about the time of driving?
- Does the toxicology result match the officer’s description of impairment?
Laboratory evidence can be important, but laboratory evidence should not be separated from the facts surrounding the stop.
Why Is THC Blood Testing Different From Alcohol Testing?
Alcohol and THC behave differently in the body.
Alcohol concentration generally has a more predictable relationship with impairment. That relationship is one reason Texas law can use a numerical alcohol concentration of 0.08 as a definition of intoxication.
THC is different.
NHTSA has reported that THC concentrations rise and fall differently from alcohol and that blood THC concentration has a poor correlation with the degree of impairment. THC levels may fall substantially during the time between consumption, driving, a traffic stop, an arrest, obtaining a warrant, and collecting a blood sample.
This is why a THC toxicology result should not simply be interpreted as though it were an alcohol BAC result.
Texas DPS also continues to update its cannabinoid testing procedures. In June 2026, DPS temporarily stopped THC testing in urine while validating new methods and again stated that blood is the preferred specimen when drugs are suspected in a DWI investigation.
Can Police Search Your Vehicle During a Drug DWI Investigation?
A DWI investigation does not automatically give police unlimited authority to search a vehicle.
A vehicle search must still be supported by a lawful basis.
Depending on the circumstances, police may claim authority to search based on consent, probable cause, a warrant, an exception to the warrant requirement, or other legally recognized grounds.
That issue can become especially important when a DWI investigation leads to the discovery of:
- Marijuana
- THC vape cartridges
- Prescription pills
- Cocaine
- Methamphetamine
- Fentanyl
- Other controlled substances
- Paraphernalia
- Bags, containers, or other items allegedly connected to drugs
The defense may need to examine the original reason for the traffic stop, how long the driver was detained, what the officer observed before the search, what the driver was asked, whether consent was actually given, and the legal justification claimed for searching the vehicle.
Evidence obtained through an unlawful search may be subject to a motion to suppress depending on the circumstances.
For more information, see Vehicle Searches and Drug Charges and Illegal Search and Seizure.
Can You Be Charged With Both DWI and Drug Possession?
Potentially, yes.
The same traffic stop can lead to multiple allegations.
Common examples might include:
- A THC vape found during a DWI investigation
- Marijuana found after a traffic stop
- Cocaine or methamphetamine discovered during a vehicle search
- Prescription medication found in circumstances police believe are unlawful
- Fentanyl or another controlled substance discovered after an arrest
- Drugs found in a vehicle occupied by several people
The DWI allegation and possession allegation should each be analyzed independently.
If drugs were found in a shared vehicle, prosecutors may still need to establish that the accused knowingly exercised care, custody, control, or management over the substance.
At the same time, possession of a substance does not automatically prove that the person consumed it or was impaired by it.
That distinction can be critical when defending both charges.
What If Several People Were in the Vehicle?
Finding drugs inside a vehicle does not necessarily establish who possessed them.
This issue often arises when drugs are allegedly found:
- In a center console
- Under a seat
- In a door pocket
- In the back seat
- Inside a backpack or purse
- In the trunk
- In a container accessible to several occupants
Texas possession cases may involve the concept of constructive possession. Prosecutors generally need evidence connecting the accused to the substance rather than relying solely on the person’s presence near it.
A separate DWI investigation may create additional questions about whether police can establish that the driver actually consumed the particular substance found in the vehicle.
See Drug Possession Defense in Texas for more information about actual possession, constructive possession, and shared vehicle allegations.
What Defense Issues May Arise in a Drug-Related DWI Case?
There is no single defense that applies to every drug DWI case.
The appropriate strategy depends on the facts, evidence, substance involved, laboratory findings, criminal history, and circumstances of the traffic stop.
Issues that may require investigation include:
- Whether the traffic stop was lawful
- Whether the detention became unlawfully prolonged
- Whether police had probable cause for the arrest
- Whether a vehicle search was lawful
- Whether a blood warrant was legally sufficient
- Whether the blood was collected and stored properly
- Whether chain of custody can be established
- Whether laboratory methods were properly followed
- Whether a drug was detected but impairment was not established
- Whether THC concentration is being overstated as evidence of impairment
- Whether the timing of THC consumption and blood collection matters
- Whether prescription medication was taken as directed
- Whether illness, fatigue, injury, anxiety, or another condition affected field sobriety testing
- Whether video contradicts the officer’s description
- Whether the DRE evaluation was performed properly
- Whether multiple drugs make the prosecution’s impairment theory uncertain
- Whether the accused actually possessed drugs found in the vehicle
- Whether statements were obtained lawfully
A possible defense is not a promised result. The evidence must be reviewed before anyone can determine which issues may matter in a particular case.
What Are the Possible Penalties for a Drug-Related DWI in Texas?
Drug-related DWI is prosecuted under the same Texas DWI statutes that apply when alcohol is alleged.
A basic DWI under Texas Penal Code § 49.04 is generally a Class B misdemeanor with a statutory minimum confinement period of 72 hours. Certain circumstances can increase the offense level.
A prior qualifying intoxication conviction can raise a later DWI to a Class A misdemeanor with a minimum confinement period of 30 days. Two prior qualifying intoxication convictions can make a later DWI a third-degree felony.
Other circumstances can also affect the charge. For example, DWI with a passenger younger than 15 is a state jail felony. Since September 1, 2025, Texas law also makes DWI committed while operating a vehicle in an active school crossing zone a state jail felony.
The possible consequences may also include:
- Fines and court costs
- Jail or prison depending on the offense level
- Community supervision
- Driver’s license consequences
- Drug or alcohol testing
- Treatment or education requirements
- Bond conditions
- Ignition interlock requirements in some cases
- Employment consequences
- Professional licensing concerns
- Increased insurance costs
- Consequences for commercial drivers
- A criminal record
Not every consequence applies to every person or every case.
What If the Toxicology Results Have Not Come Back Yet?
Drug toxicology testing is not instantaneous.
A person may therefore be dealing with a pending DWI case while important laboratory questions remain unanswered.
Those questions may include:
- What substances were detected?
- Was THC detected?
- Were prescription drugs detected?
- Were multiple substances present?
- What concentrations were reported?
- Do the results support what the officer claimed to observe?
- Does the testing raise additional scientific or legal issues?
Texas DPS has taken steps in recent years to address a substantial drug toxicology workload. DPS reported that its toxicology drug backlog was reduced by more than 50 percent during 2024, and the agency continued updating cannabinoid toxicology procedures in 2026.
A pending laboratory report should not be treated as though its conclusions are already known.
What Should You Do After a Drug-Related DWI Arrest?
The hours and days after an arrest can be confusing, especially when you do not yet know whether the case involves DWI, drug possession, or both.
Start by focusing on three steps.
Tell Us What Happened
Write down what you remember about the stop while the details are fresh.
Important information can include:
- Why the officer said you were stopped
- What questions you were asked
- Whether you were asked about drugs or medication
- What field sobriety tests were performed
- Whether another officer or DRE arrived
- Whether your vehicle was searched
- What police claimed to find
- Whether you consented to a search
- Whether blood was requested
- Whether a warrant was obtained
- Where and when blood was collected
- Who else was in the vehicle
Do not guess about facts you do not remember.
Understand the Case
Next, determine exactly what the government is alleging.
You may be facing:
- DWI
- Drug possession
- Both DWI and possession
- A prescription drug allegation
- A THC concentrate charge
- Marijuana possession
- Another drug offense discovered during the vehicle search
The elements and evidence may be different for each charge.
Build a Path Forward
A defense can then focus on the actual evidence.
That may include police reports, body camera footage, dash camera footage, search warrants, blood draw records, laboratory reports, toxicology evidence, photographs, vehicle evidence, prescription records, and witness information.
For additional guidance, see What to Do After a Drug Arrest.
How Dr. Newton Can Help With a Drug-Related DWI Case
A drug-related DWI case may require more than simply asking whether a blood test was positive.
The entire investigation matters.
Dr. Lloyd A. Newton can examine the traffic stop, officer observations, field sobriety testing, DRE evaluation, vehicle search, alleged drug possession, blood collection, search warrant, toxicology report, and the legal connection between any detected substance and the prosecution’s claim of impairment.
When DWI and drug charges arise from the same incident, he can also evaluate how the evidence supporting one allegation affects the other.
The goal is to understand what the government can prove, identify weaknesses or legal issues in the evidence, and build a defense strategy based on the facts.
Dr. Newton represents people facing drug-related DWI and drug charges throughout Texas.
Tell Us What Happened
Explain what happened during the stop, search, arrest, and blood collection.
Understand the Case
Identify the charges, evidence, laboratory issues, and legal questions that may affect the case.
Build a Path Forward
Develop a defense strategy based on the facts and the law.
Frequently Asked Questions About Drug-Related DWI in Texas
Can you get a DWI for marijuana in Texas?
Yes. Texas DWI law is not limited to alcohol. A person may be accused of DWI if marijuana or THC allegedly caused the loss of normal mental or physical abilities while operating a motor vehicle in a public place. The prosecution still must prove the required elements of DWI.
Is there a legal THC limit for driving in Texas?
Texas does not currently use a numerical THC concentration that automatically establishes intoxication in the same way that an alcohol concentration of 0.08 can. THC-related DWI cases generally require examination of impairment evidence along with toxicology and the surrounding circumstances. NHTSA research has found that blood THC concentration does not correlate with impairment as predictably as alcohol concentration.
Can you get a DWI for prescription medication?
Yes. Having a valid prescription does not automatically prevent a DWI allegation. Texas law can treat a person as intoxicated when a drug causes the loss of normal mental or physical abilities. Whether the medication actually caused impairment depends on the evidence and circumstances.
Can I be charged with DWI if I did not drink alcohol?
Yes. Texas DWI can be based on controlled substances, drugs, dangerous drugs, combinations of substances, or other substances. Alcohol is not required.
Does THC in my blood prove I was impaired?
Not automatically. A blood test can be important evidence, but NHTSA has found a poor correlation between THC blood concentration and the degree of impairment. Timing, consumption method, officer observations, toxicology results, and other evidence may all matter.
Can I be charged with both DWI and drug possession?
Yes, depending on the circumstances. Drugs found during a DWI investigation may lead to a separate possession allegation. However, evidence of possession does not automatically establish impairment, and a DWI allegation does not automatically establish possession.
Can police search my car after a drug DWI arrest?
Not automatically. Police still need a lawful basis for the search. The legality of the traffic stop, detention, arrest, consent, probable cause, warrant, and any claimed exception to the warrant requirement may need to be examined.
What happens if the blood test takes a long time to come back?
The case may remain pending while toxicology testing is completed. Until the report is available, important questions about which substances were detected and what the results may mean can remain unresolved. The eventual laboratory report should be reviewed together with the traffic stop, video, officer observations, blood collection records, and other evidence.
Get Help With a Texas Drug-Related DWI Charge
A traffic stop involving THC, prescription medication, marijuana, or another drug can become more complicated than expected. You may be facing questions about impairment, possession, a vehicle search, a blood test, or several of those issues at the same time.
You do not have to guess what the evidence means or what happens next.
Dr. Lloyd A. Newton represents clients facing drug-related DWI and drug charges throughout Texas. He can review what happened, explain what the prosecution may need to prove, and help you understand the options available based on the facts of your case.
This page provides general information about Texas law and is not legal advice. Laws and procedures may change, and the outcome of any case depends on its individual facts. Viewing this website or contacting the firm does not by itself create an attorney-client relationship.
Last reviewed: September 3, 2026