FAQ 4

The Governor’s Highway Safety Association issued a state by state report in January 2015.  They report that “19 states have strict per se laws that forbid any presence of a prohibited substance or drug in the driver's body while in control of the vehicle.”  Their web page on this issue also has a lot of other information about this issue and efforts to reduce drugged driving.

http://www.ghsa.org/html/stateinfo/laws/dre_perse_laws.html