Can I be tested by a police officer for DUI if I only smoked marijuana before I drove?

​Yes, under California Vehicle Code section 23152(e), driving under the influence of drugs, legal or illegal, is a criminal offense.  If you are the driver of a vehicle and contacted by an officer who suspects you are under the influence of marijuana either due to your admission of smoking marijuana or by observing physical symptoms of drug use, then you can be arrested for DUI.