The same statute that makes drunk driving a crime in Texas also covers drugged driving. As it applies to drugs, this law defines "driving while intoxicated" (DWI) as operating a motor vehicle while "not having the normal use of mental or physical faculties" due to ingesting drugs.
Texas's drugged driving law applies to a broad range of intoxicating substances. The law applies to "a controlled substance, a drug, a dangerous drug, a combination of two or more of those substances, or any other substance into the body."
This definition, of course, includes common drugs like marijuana, cocaine, methamphetamine, and opiates. Basically, a motorist can get a drug DWI for operating a vehicle while impaired by any substance. And it's no defense that the drug or controlled substance was prescribed by a doctor.
A driver who's arrested for drugged driving in Texas will generally be facing the same penalties that apply to an alcohol-related DWI. So, the possible fines, jail time, and other consequences of a drug-DWI conviction depend on whether it's a first, second, or third offense. A DWI conviction is considered a prior offense for purposes of calculating punishment regardless of whether it involves alcohol, drugs, or a combination of the two.
Texas's "implied consent" law requires all drivers lawfully arrested for driving while intoxicated by drugs or alcohol to submit to blood testing when requested to do so by an officer. Refusal to take a test will result in license suspension and can be used against the driver at a DWI trial.