Prescription for Use of Drug No Defense to DWI - Texas Penal Code Section 49.10
§ 49.10. No Defense.
In a prosecution under Section 49.03, 49.04, 49.045, 49.05, 49.06, 49.065, 49.07, or 49.08, the fact that the defendant is or has been entitled to use the alcohol, controlled substance, drug, dangerous drug, or other substance is not a defense.