DUI Marijuana California Guidelines

January 1, 2018 marked the day that the possession of up to one ounce of recreational marijuana became legal in California for people over 21. California was the sixth state to introduce the sale of recreational marijuana.

California law does not prohibit a certain amount of a given drug in a person’s system. The law simply prohibits a person from “driving under the influence” of a drug: it must affect a driver so that their mental or physical abilities are so impaired that he or she is no longer able to drive a vehicle with the caution of a sober person, using ordinary care, under similar circumstances — the same definition as for driving under the influence of alcohol. This is a notoriously vague and subjective standard of proof.

A driver can be using marijuana or prescription drugs legally, but just as with the legal use of alcohol, they can be charged with driving under the influence if they are impaired. See ‘‘How Legal Drug Use Can Lead to a DUI or DWI’’.

Does Marijuana Cause Impairment?

Does marijuana cause impairment of driving ability? There is considerable evidence that it does not. A review conducted in 2002 of seven separate studies of over 7,000 drivers involved in car accidents concluded that “crash culpability studies have failed to demonstrate that drivers with cannabinoids in the blood are significantly more likely than drug-free drivers to be culpable in road crashes.”

Two separate studies conducted by the U.S. Department of Transportation have come to similar conclusions. In one, researchers concluded that “although alcohol was found consistently and significantly to cause impairment, marijuana had only an occasional effect.” In the other study, researchers found that THC is not a profoundly impairing drug…It apparently affects controlled information processing in a variety of laboratory tests, but not to the extent which is beyond the individual’s ability to control when he is motivated and permitted to so in driving.” See Does Marijuana Affect Driving Ability?for more.

Chemical Testing

If you are pulled over by an officer, California law carries implied consent of an individual to submit to a blood or urine test. There is no exception for law-abiding medical cannabis patients. Drivers can choose between submitting to a blood test or a urine test. (A breath test does not show the presence of marijuana.) However, refusal of a chemical test will result in a fine, mandatory imprisonment in the case of a DUI conviction, and a license suspension for one year. In addition, refusal to take a chemical test is admissible as evidence of guilt in a court of law.

Another test that law enforcement officers can employ is a saliva swab. At some DUI checkpoints, officers administer this test. It takes about 8 minutes to produce results. The swab can detect trace amounts of THC. However, it cannot determine when cannabis was consumed, nor if the amount detected is enough for the user to be considered “impaired.”


When it comes to possession of cannabis in a vehicle, there is an open container law for marijuana similar to the law for alcohol. It is unlawful to drive with any marijuana that is not in a container or that is in a container that has been open or has a broken seal. Opened containers containing cannabis must be locked away in the trunk. Violation of this law is an infraction punishable by a fine of no more than $100.

If you are driving in possession of more than the legal amount of marijuana, (i.e. more than 28.5 grams of marijuana or more than 4 grams of concentrated cannabis), you are no longer in possession of marijuana “as authorized by law.” You can face a fine for driving in possession of marijuana and a misdemeanor charge.

People under the age of 21 are only permitted to drive with marijuana in the vehicle in accordance with medical marijuana laws. Consequently, if you are under 21, you could get charged with illegal possession of marijuana if you are not a medical user—even if the container is sealed and unopened.

Remember, although chemical testing for marijuana use is often inaccurate, be safe and avoid mixing marijuana use and driving. While recreational usage is legal, any impairment due to cannabis while driving can be a felony. Be careful not to keep open containers of marijuana in the cabin of your vehicle.

Administrative License Suspensions

With alcohol-related DUI, the DMV can impose an “administrative suspension” on their license if someone refuses the chemical test or has a BAC above 0.08%. In DUI Marijuana situations, there is not a specific amount of drugs that can cause an “administrative suspension.” The DMV can, however, impose a suspension if a person was lawfully arrested for a DUID and refused chemical testing, and also if a person is convicted of any DUI charge in criminal court.


  • You weren’t driving.
  • You didn’t use marijuana.
  • You used marijuana, but you were no longer high when you drove.
  • Your mental and physical abilities weren’t significantly impaired.