Cannabis and Driving

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December 29, 2017 - With adult-use cannabis stores opening in California on January 1, Cal NORML reminds our members, tourists coming in to California, and others of the following:

Using marijuana can impair your ability to drive safely. Signs of marijuana impairment include:

• Loss of concentration and attentiveness.
• Impaired reaction time and emergency decision-making ability.
• Reduced peripheral vision.
• Difficulty maintaining a constant speed, following distance, and lane position.
• Loss of balance.
• Getting lost even in familiar places.

Cannabis use is substantially less dangerous than drunken driving, using a cell phone, and other risky driving behaviors, but can be serious for heavy doses, such as from dabs or edibles. Everyone should be aware of their level of impairment before they drive, most especially those who are unaccustomed to being “high” on marijuana.

The use of cannabis edibles can be particularly problematic to drivers. Edibles typically don’t take effect for 1-2 hours or more after ingestion, and it can be difficult to know the proper dosage. A 10mg THC dose is considered a full dose for edibles, but inexperienced users are advised to start lower, between 2.5 – 5 mg. (Experienced chronic users can tolerate much higher doses.) All should take edibles only in an environment that is safe to themselves and others.

Combining marijuana with alcohol can be especially dangerous, most studies show. It’s wise not to mix the two, especially before driving.

Cal NORML recommends cannabis consumers download an impairment-measuring app on their phones, such as My Canary or DRUID. Using one of these apps, you can establish a baseline level of performance on tests that correlate to driving functions, and test yourself after consuming cannabis and before getting on the roadway. (Don’t, of course, use one of these smartphone apps while you’re driving!) Absent one of these, try standing on one foot to check your balance.

Using cannabis while in a car, or driving under the influence of cannabis, remain illegal in California. Although California has no per se limit on the amount of THC in a driver's body, officers may administer a field sobriety test and arrestees may also be required to submit to a blood or urine test or else forfeit their licenses. Read more.

Also see:

  • NORML Fact Sheet on Psychomotor Performance and Marijuana
  • "Drug Test Results and Accident Risks" from Cal NORML Guide to Interpreting Drug Test Results
  • Overview of Oral Fluid Testing 2/25/17
  • Marijuana and Driving

    Founded in 1972, California NORML is a non-profit, membership organization dedicated to reforming California's marijuana laws. We are the only state organization devoted specifically to marijuana reform for consumers. We publish a newsletter, lobby lawmakers, sponsor events, offer legal, educational, and consumer health advice, and sponsor scientific research.