Denton DWI Defense Lawyer: Driving While on Drugs

taking drugs while driving

DWI Defense Attorney Answers Legal Questions

Defending Drivers in the Lewisville, Denton, and Frisco Areas

Where alcohol is involved, before the State can admit the blood test results to show the driver was drunk, the State’s expert (usually a lab technician) must testify on (1) time of ingestion, (2) the amount of the BAC and (3) the speed that alcohol is absorbed and eliminated by the body. This is the typical procedure for getting blood test results admitted at trial to show driving while intoxicated on alcohol. Alcohol, however, is not the only substance that can get you a DWI.

You can get a DWI while drugs are in your system, no alcohol necessary. In Texas, a person commits the offense of Driving While Intoxicated “if the person is intoxicated while operating a motor vehicle in a public place.” TEX. PENAL CODE § 49.04(a). “Intoxicated” is defined 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.” TEX. PENAL CODE § 49.01(2)(A).

Testing drugs in DWI cases presents its own unique challenges because new drugs are constantly appearing on the streets. When little is known about the drug’s effects on the body’s normal function, how long it takes to show those effects, and how the body eliminates and absorbs the chemical (the come-down), it is difficult to quantify if a person had enough of that drug in their system to be “intoxicated.” Further, it makes a huge difference how long ago the drug was taken to prove the person was actually driving while intoxicated on the drug.

Question: does the State have to prove all the same information as an alcohol case before it can show the jury the blood test results for a drug intoxication case?

Answer: No.

In Ashby v. State, the Texas Court of Criminal Appeals held that testimony regarding the time of ingestion, quantification of the drug in the defendant’s blood stream, and the pharmacokinetics of a new drug is not required before the blood evidence is admitted. A stark contrast to alcohol cases. After being stopped and placed under arrest for suspicion of DWI, Mr. Ashby volunteered to provide a blood sample. The drug in Ashby’s blood results was Trifluoromethylphenylpiperazine (“TFMPP”), a controlled substance under section 481.103(a)(1) of the Texas Health & Safety Code. TFMPP is a new designer drug or ‘party pill’ and has become popular among young adults as an alternative to methamphetamine and MDMA (Ecstasy). However, there is no information currently available describing the acute neurophysiological effects of these psychoactive drugs in humans.

Because scientists don’t really understand how TFMPP affects the human brain, the State had a problem proving the defendant was legally intoxicated at the time he was driving. Normally, since we know a lot about how alcohol affects humans, the State can show that a person had X-number of drinks X hours before getting behind the wheel and X hours before getting their blood drawn. That’s how the blood results of 0.08 BAC is admissible to show the jury. We know how to measure alcohol. But how can a doctor or scientist say how intoxicated a person is on a drug when they don’t know how long it takes to kick-in and what the full effects are after taking it? Simply, they can’t. The State’s expert couldn’t testify about absorption and elimination rates and estimated time of ingestion because no human studies of TFMPP had been completed. But the State put a doctor on the stand, who could say what little he did know about the drug. And the trial court allowed it. After his expert challenge under rule 403 was overruled, Mr. Ashby took a plea.

The Court of Criminal Appeals held failure to quantify the amount of the drug and estimate the time of ingestion might lessen the probative value of the evidence, but it does not render it unreliable or irrelevant. So the State got to present what evidence they had on TFMPP’s effects, even if it was questionable evidence at best. The Court reasoned that although no human studies of TFMPP had been conducted yet, the expert demonstrated he knew everything there was to know about the new drug.


If you have been arrested for or charged with driving under the influence of drugs, call our office to schedule a free consultation with an experienced DWI defense attorney.