Jose Ceja, a former prosecutor and Board-Certified Criminal Law Specialist, has received extensive training in blood testing and toxicology. He defends individuals charged with drug-based DWI throughout Houston and Harris County. Ceja Law Firm uses expert analysis, toxicology review, and aggressive legal strategy to challenge every aspect of the case.

What Counts as a Drug in a Texas DWI Case?

Under Texas law, any substance that impairs your mental or physical faculties can support a DWI charge. This includes:

  • Prescription medications: Xanax, Ambien, Adderall, painkillers, etc.
  • Over-the-counter drugs: Diphenhydramine (Benadryl), NyQuil, sleep aids
  • Illegal drugs: THC (marijuana), cocaine, methamphetamine, ecstasy
  • Combination of substances: Even small amounts of alcohol + drugs can lead to charges

The legal issue is not whether the drug was legal, but whether it impaired your ability to safely operate a vehicle.

What Is the Legal Definition of Drug-Based Intoxication in Texas?

Texas Penal Code §49.01(2) defines intoxication as:

“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.”

There is no defined quantity or legal limit for most drugs in Texas. Unlike alcohol (which has a 0.08 BAC threshold), drug-based DWI cases rely heavily on officer opinion, field sobriety tests, and blood testing—all of which can be challenged.

Drug DWIs Are Handled Differently Than Alcohol-Based DWIs

Unlike alcohol, drugs do not metabolize in the body in a consistent or predictable way. The presence of a drug in your system does not necessarily mean you were impaired at the time of driving. For example:

  • THC can remain in the bloodstream for days or weeks after use, long after any impairing effect has worn off.
  • Benzodiazepines and opioids may show up at therapeutic levels that do not cause impairment.

That’s why Ceja Law Firm frequently retains independent toxicologists to challenge the State’s conclusions and explain how drug metabolism differs from alcohol. We also evaluate whether law enforcement followed proper testing protocols and whether any signs of actual impairment were present.

How Are Drug DWIs Investigated?

Officers who suspect drug use typically follow a different investigative process:

  • Field sobriety tests (FSTs), often not designed for drug impairment
  • Questioning about recent drug use or prescriptions
  • Drug Recognition Expert (DRE) evaluations (in some cases)
  • Blood draw (typically via warrant)
  • Lab toxicology screening

Each of these steps presents opportunities to challenge the case. DREs, for example, often lack medical training and rely on subjective observations. Their conclusions can be inconsistent and unscientific.

What Is a Drug Recognition Expert (DRE)?

A Drug Recognition Expert (DRE) is a specially trained police officer who conducts evaluations to determine whether a person is under the influence of drugs. These evaluations follow a 12-step protocol that includes vital signs, pupil measurements, muscle tone, and divided attention tests.

While DREs are often portrayed as experts, their conclusions are subjective, based on non-medical training, and often not backed by scientific evidence. Courts do not always treat DRE findings as reliable, especially when:

  • The DRE did not complete the full 12-step evaluation
  • The evaluation was based on guesswork or bias
  • Medical explanations (fatigue, illness, anxiety) were ignored

At Ceja Law Firm, we challenge DRE reports by highlighting procedural flaws, using expert testimony, and pointing out contradictions between the DRE’s findings and the blood test results.

How Is Blood Tested for Drugs?

Blood samples in drug DWI cases are typically analyzed using gas chromatography-mass spectrometry (GC-MS) or liquid chromatography-mass spectrometry (LC-MS/MS). These methods can detect minute levels of substances but do not indicate actual impairment.

Key issues Ceja Law Firm investigates include:

  • Whether the blood draw was properly authorized (warrant or valid consent)
  • How long after driving the blood was drawn (timing can affect accuracy)
  • Chain of custody and contamination risks
  • Whether detected drugs are active or inactive metabolites
  • If a toxicologist was involved in interpreting the results

What types of DWI charges can be based on drugs?

Almost any type of DWI charge in Texas can be based on drug intoxication—not just alcohol. If prosecutors believe that a person lost the normal use of their mental or physical faculties due to drugs (even prescribed medications), they may pursue charges such as:

  • First-time DWI – Even a first offense can be based solely on drugs like THC, Xanax, or Ambien.
  • DWI with a child passenger – Driving while impaired by drugs with a child in the vehicle is a felony in Texas.
  • DWI second offense or Felony DWI – Prior alcohol-related convictions don’t stop prosecutors from alleging drug intoxication in later cases.
  • Intoxication assault – Causing serious injury while driving under the influence of drugs may lead to a second- or third-degree felony.
  • Intoxication manslaughter – If a fatal accident occurs, drug intoxication can lead to a second-degree or even enhanced first-degree felony.

Drug-based DWI charges are highly fact-specific and often defensible. Ceja Law Firm evaluates every aspect of the case—including toxicology, officer observations, and causation—to build the strongest possible defense.

How Drug DWIs Are Prosecuted in Houston

In Harris County, prosecutors take drug-related DWIs seriously—even for first-time offenders. These cases are typically filed by the Harris County District Attorney’s Office and assigned to experienced misdemeanor or felony prosecutors, depending on the charge. Prosecutors may rely heavily on lab results and DRE opinions, which makes it critical to retain an attorney who understands how to challenge both.

Common Defenses in Drug DWI Cases

Some of the most effective defenses include:

  • No evidence of actual impairment (despite presence of a substance)
  • Medical condition mistaken for impairment (e.g., fatigue, anxiety, diabetes)
  • Contaminated or mishandled blood samples
  • Improper field sobriety test administration
  • Unqualified DRE conclusions
  • Invalid traffic stop or lack of probable cause

Drug-based DWIs are often more defensible than alcohol-based cases because they rely on subjective evidence and disputed science. Our firm regularly works with forensic toxicologists to identify weaknesses in the State’s theory.

Penalties for Drug DWIs in Texas

Penalties are similar to alcohol-based DWIs and increase with aggravating factors:

  • First Offense (Misdemeanor): Up to 180 days in jail, up to $2,000 fine, 1-year license suspension
  • Second Offense: Up to 1 year in jail, up to $4,000 fine, mandatory ignition interlock
  • Third or More (Felony): 2 to 10 years in prison, up to $10,000 fine
  • With Child Passenger: State jail felony (6 months to 2 years)
  • Causing Serious Injury or Death: Intoxication assault or manslaughter (2 to 20+ years)

Drug DWIs can also lead to ALR driver’s license suspension, even before conviction.

Immigration Consequences of Drug DWIs

Drug-related DWIs can be especially dangerous for non-citizens. They may be classified as:

  • Crimes involving moral turpitude
  • Controlled substance violations
  • Aggravated felonies (if injury or death involved)

These can result in removal proceedings, inadmissibility, or denial of adjustment of status. Ceja Law Firm works with immigration counsel when necessary to protect your immigration future.

Frequently Asked Questions (FAQs)

Can I get a DWI for taking my prescription medication?

Yes. Even if prescribed, if the drug impairs your ability to drive, you can be charged. However, prescription use may provide a valid defense, especially if taken as directed.

Is there a legal limit for THC or other drugs in Texas?

No. Texas does not have a “per se” limit for THC or most other drugs. Prosecutors must prove actual impairment—not just presence.

Do I have to be “high” to be charged with a drug DWI?

Not necessarily. If the officer believes you lacked normal use of your faculties due to drug influence, even without signs of euphoria or visible intoxication, you can be charged.

Can I refuse a blood test?

You can refuse, but police may obtain a search warrant for your blood. Refusal can also lead to administrative penalties like license suspension.

What if a drug is detected but I wasn’t impaired?

This is a common issue. Many drugs stay in your system after effects have worn off. Expert testimony from a toxicologist can help challenge the assumption that you were impaired.

Is it easier to prove intoxication by alcohol or drugs?

It is generally easier for the State to prove alcohol-related DWIs because of the 0.08 BAC standard. Drug-based DWIs are often harder to prove because they rely on subjective officer observations, questionable DRE evaluations, and the presence of drugs that may not have caused impairment. This is why drug DWI charges are often more defensible with a skilled attorney.

Speak with a Houston Drug DWI Defense Lawyer Today

If you’ve been charged with driving while intoxicated by drugs, it’s critical to work with a defense lawyer who understands the science behind the charge. Ceja Law Firm regularly defends clients in complex drug DWI cases and works with toxicologists and forensic experts to uncover the truth and protect your future. Contact us today for a free consultation with a Board-Certified Houston criminal lawyer.