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Drug Impairment

Most people associate driving while intoxicated (DWI) offenses with alcohol. However, Texas law states this isn’t always the case. Driving while impaired on drugs is also a criminal offense in the state of Texas. A person charged with a DWI may have to face large fines and possible incarceration.

The law has created a standardized way to determine how drunk a person is, but there is no way to calculate if a person is impaired by drugs. Law enforcement rely on field sobriety tests and chemical testing to assess a person’s level of impairment. These tactics aren’t always accurate and can give skewed results.

If you or someone you know has been charged with a DWI, it’s vital that you gain trusted legal representation.

Houston Attorney for Drug-Impaired DWI in Texas

A DWI conviction can result in multiple penalties including expensive fines and possible jail or prison time. Chemical or field sobriety tests results may paint a picture for the jury that you were under the influence of drugs. It’s important that you confront your DWI charges with a strong defense. Call Matthew Horak now at (713) 225-8000 and start the first plans to your defense plan today. 

Attorney Matthew Horak has years of experience defending those with drug-impaired driving charges. He is passionate about defending Texas residents and approaches each case with renewed vigor. Gain not just an attorney but a legal partner with Horak Law.

Contact Matthew Horak at (713) 225-8000 and set up a free consultation today. Horak Law has offices located in Houston and The Woodlands. Horak Law serves communities throughout the greater Harris County area including surrounding counties such as Liberty County, Fort Bend County, Montgomery County, and Waller County.

Overview of Drug-Impaired DWIs in Texas

Driving While Impaired on Drugs Laws in Texas

It’s unlawful in Texas to operate a motor vehicle while impaired on drugs or alcohol. Texas law defines impairment in two different ways. One is that the alleged offender is unable to retain or has difficulty using their full mental and physical faculties due to the use of drugs or alcohol. The second way to determine intoxication is by measuring blood-alcohol concentration (BAC). 

For alcohol, the law can easily interpret whether a person is impaired or not. A person who has a BAC of .08 or higher is considered intoxicated under Texas law. On the other hand, drugs such as marijuana are harder to calculate impairment.

Currently there is no standardized way to measure the level of drugs in an impaired driver’s system. In fact, it may be impossible due to the variety of effects that different drugs can have. Law enforcement and district attorneys are forced to use chemical testing, field sobriety tests, and objective evidence to convict a person of drug-impaired driving. These tests are arguably questionable and can give misleading results.

Penalties for Drug-Related DWIs in Texas

The legal consequences for drug-impaired driving are the same as a DWI for alcohol. If the alleged offender has a controlled substance on his or her person, they may have added possession charges. The following chart details the penalties a person may face if he or she was convicted of a drug-related DWI.


Number of Offenses:

Offense Level:

Jail/Prison Time:


First Offense

 Class B Misdemeanor

Minimum of 72 hours in jail; maximum of 180 days in jail


 Second Offense

 Class A Misdemeanor

 Minimum of 30 days in jail; maximum of 12 months in jail.


 Third Offense

 Third-Degree Felony

 Minimum of 2 years in prison; maximum of 10 years in prison.



A person with a DWI conviction may be required to complete additional conditions for their sentencing which may include:

  • Mandated community service;
  • Drug and alcohol evaluation;
  • If eligible, participation in a court-ordered program;
  • Installation of an ignition interlock device (IID); and
  • Yearly surcharges by the Texas Department of Public Safety.

DWI Testing in Texas

Law enforcement uses various standardized tests to measure a person’s level of impairment.  Typically, officers will either use field sobriety tests or types of chemical testing to confirm if a person is under the influence or not. Both of these tests have been known to produce false results.

Police officers usually use field sobriety tests first to assess if a person is impaired. These tests are a series of physical exercises that the National Highway Traffic Safety Administration (NHTSA) developed to measure a person’s reflexes and awareness.

The following are the three field sobriety tests that the NHTSA developed for police officers. 

  • Horizontal Gaze Nystagmus (HGN) – This test measures a phenomenon called nystagmus, which is the involuntary twitching of the eye when a person is under the influence of drugs or alcohol. Law enforcement will hold a pen 12 to 15 inches away from the driver’s nose and sway the object from side to side. If the alleged offender has issues tracking the pen, it’s a supposed sign that the driver is intoxicated.
  • One-Leg Stand (OLS) – OLS is exactly as the name implies. A police officer will ask the driver to stand on one foot about six inches off the ground. Normally, the driver will be asked to count for 30 seconds in the thousands. If the alleged offender cannot keep balance, it’s allegedly a sign of impairment.
  • Walk-and-Turn (WAT) – In a walk-and-turn test the police officer will ask the driver to take nine heel-to-toe steps on a straight line. After the driver has reached the end of the line, he or she will turn on one foot and take another nine heel-to-toe steps back. Drivers who are unable to stay on the line or do the steps are allegedly impaired.

A multitude of factors can affect field sobriety testing. Simple outside stimuli such as cars can completely ruin an HGN test. On the other hand, if a person has a physical disability or illness he or she may have a lot of difficulty performing a WAT or OLS test.

The next set of tests that law enforcement may turn to is chemical testing. Police officers will ask drivers to submit bio-samples and send them over to a state or private crime laboratory. Law enforcement analysts will measure if any drugs are present in the given samples. If drugs are found, then they may be able to use that evidence in court.

The following are the three types of chemical testing used by law enforcement.

Chemical testing isn’t a flawless process. Many outside factors can influence testing and lead to misleading results. A blood or urine sample could be mishandled and tainted. At the same time, a breathalyzer could be malfunctioning and be giving skewed results because of poor maintenance.  

Texas has a set of rules regarding chemical testing, which is called the “implied consent laws.” The laws state that Texans are implicitly agreeing to comply with chemical testing if they are using public roads. Refusal to submit to chemical testing can result in an administrative license revocation (ALR). An ALR will lead to a driver’s license suspension for up to 180 days, and the refusal to submit to testing can be used against you in trial.

Since chemical testing is so subjective and problematic, a skilled attorney can contest any evidence gathered from field sobriety tests. Additionally, your attorney may be able to file a request for an administrative license suspension hearing, which will give you an opportunity to regain your license.

Drug Recognition Experts in Houston, Texas

Law enforcement are finding new ways to battle drug-impaired drivers. The International Association of Chiefs of Police (IACP) has created a curriculum to help police officers identify people under the influence of drugs. Officers who successfully complete the program gain the title of Drug Recognition Expert (DRE). 

Drug recognition experts uses a 12-step process to evaluate the normal faculties of a person. These steps include:

  • Breath-alcohol test;
  • Asking the driver questions to assess their state;
  • Preliminary examination that uses eye-tracking exercises and compelling questions;
  • Evaluating the eyes using the Horizontal Gaze Nystagmus (HGN), the Vertical Gaze Nystagmus (VGN), and Lack of Convergence (LOC).
  • Field sobriety tests such as the walk-and-turn, one-leg stand and finger-to-nose;
  • Examining vital signs such as pulse, blood pressure and body temperature;
  • Assessing the pupil size with a pupilmeter and penlight;
  • Checking the driver’s muscle tone;
  • Examining the driver’s arm for any injection sites;
  • Asking the driver about suspicious evidence or the DRE process;
  • Documenting the results of the DRE evaluation; and
  • Obtaining a urine or blood sample for analysis.

Common Prescription Drugs that Can Impair Your Driving

While most people think of illegal drugs when it comes to DWI, in actuality this isn’t always the norm. The Governors Highway Safety Association reported that 42 percent of people driving impaired on drugs weren’t using opioids or marijuana, but instead were using other prescription drugs. 

Even though taking a prescribed drug and driving is legal, it can still result in a DWI. Some commonly prescribed medications can significantly affect a driver’s ability to operate a vehicle. The following are some prescriptions that can impair a person’s driving. 

  • Valium;
  • Ativan;
  • Xanax;
  • Hydrocodone;
  • Sleeping pills;
  • Specific antidepressants;
  • Anti-anxiety drugs; and
  • Products with codeine.  

Additional Resources 

Texas DWI Laws – Visit the official website for Texas Penal Code and find more information about DWIs and other related offenses. Learn the penalties for a DWI, the aggravating factors that can affect a DWI conviction, and admissible defenses in court.

Drugged Driving – Visit Get Smart About Drugs, a resource for parents, educators, and caregivers by the Drug Enforcement Administration (DEA). Here you can find infograms detailing drug-related DUI statistics and data, answers to frequently asked questions, and find other articles related to drug or alcohol use. 

DWI Lawyer for Drug Impaired Driving in Harris County, Texas

Have you been accused of driving impaired while on drugs? If so, you must start your defense now. A DWI conviction can lead to heavy fines, community service, completion of a court-ordered program, annual surcharges, and possible incarceration.

Matthew Horak is a practiced attorney with years of experience in criminal defense. Rest assured, Matthew Horak will do whatever that’s possible to defend your rights. With his resources, skills, and knowledge Matthew Horak can steer you in the right direction. 

Call today at (713) 225-8000 and schedule a free consultation today. Horak Law represents those accused of a DWI throughout the greater Houston metropolitan area and surrounding communities including Greenspoint, Midtown, Meyerland, Brays Oaks, and River Oaks.

This article was last updated on November 27, 2018.

  • Texas Board of Legal Specialization | Criminal Law
  • National College for DUI Defense
  • National Association of Criminal Defense Laywers
  • Harris County Criminal Lawyers Association
  • Matt Horak has earned recognition for community leadership by Lawyer Legion