According to California state statutes on impaired driving, you can
be convicted of California DUI even if you haven't had a single drink.
Driving under the influence of drugs is just as illegal as drinking and
driving. It doesn't matter if the drugs are legal or illegal. In fact,
Section 23630 of the Vehicle Code states that even if a person is
entitled to use a particular drug, it's still a crime to drive under
the influence of a drug. If the police officer believes you are DUI
from being under the influence of a drug other than alcohol, you will
be required to provide either a blood test or a urine test.