Driving under the influence of marijuana is a DUI in California, just like driving under the influence of alcohol. It doesn't matter if you're over 21 or if you have a doctor's recommendation to use medical marijuana. Think of weed like alcohol -- just because you're allowed to possess it doesn't mean that you're allowed to operate a vehicle while you're under the influence.
The big difference between marijuana and alcohol is that there's no legal limit for THC and no reliable way to determine a driver's degree of impairment with weed. Blood, urine and saliva tests cannot accurately tell us whether or not a subject is dangerously intoxicated by marijuana. This means that marijuana DUIs are pretty arbitrary. They often turn on the police officer's opinion based on his observations before and after the traffic stop. The factors that I usually see listed in police reports include:
- Bad driving
- Smell of marijuana coming from the interior of the vehicle
- Driver observed smoking in a moving vehicle
- Red, glassy eyes
- Any signs that the driver is disoriented or has difficulty following instructions, etc.