Reply #11: The same way they arrest for other drugs.

[Xithras]

Alcohol gets all the press, but people get nailed for DWI while on over the counter and prescription meds all the time.

They will simply administer the standard field sobriety test. If you can pass it, you're not DWI. If you can't, you are DWI. Under California's laws, the police don't actually need to show which drugs you're taking. They merely need to show that your coordination and reaction times are poor enough to present a hazard. If they can do so in front of a camera where a jury can see it, there's no need for specifics.

Believe it or not, people were convicted of DUI/DWI violations LONG before fancy breathalyzers and BAC tests were invented. In situations where the new tests can't be used, the old laws and standards still apply.