While something referred to as DUI and DWI exists in every state, each state has their own particular legal definition of these terms.
In Texas, “intoxication” includes alcohol, illegal drugs, and even legal drugs. Thus, anyone operating a motor vehicle while under the influence of an intoxicating substance can be charged with a DWI. If you were or appeared to be impaired by the use of drugs or alcohol while driving, an arrest and DWI allegation is likely. However, a blood alcohol level of .08 or greater is required for conviction in the case of an alcohol-related DWI.
In Texas, a DUI is a Class-C misdemeanor charge that is applicable to drivers under the age of 21. A DUI can be charged when any amount of alcohol (even below .08) is detected.