California’s DUI laws can be complex and confusing. In this section, our attorneys break down the rules and explain the process.
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While researchers are currently trying to create a workable breathalyzer-type device to test for THC, or the psychoactive compound in marijuana, modern breathalyzers cannot detect THC or weed.
Rather, police officers currently rely on field sobriety tests and tests that examine saliva and blood to help determine if you are under the influence of marijuana. Law enforcement may also rely on a drug recognition expert (DRE).
Note that while many states have legalized the recreational and medicinal use of marijuana, it is still a criminal offense to drive while high on cannabis.
Most states say that you are guilty of driving under the influence of drugs (DUID) if:
If guilty of DUID, you could face some of the following penalties:
Current breathalyzer tests cannot detect THC (or tetrahydrocannabinol) or cannabis use. The same holds true for ignition interlock devices (IIDs).
Though researchers are trying to create a roadside testing device that police can confidently use to measure levels of THC in your breath sample.
For example, researchers at the University of Pittsburgh have successfully created a marijuana breathalyzer prototype that can detect THC levels in a breath test. The researchers, led by Alexander Star, PhD, created the new breathalyzer by using carbon nanotubes, or tiny tubes of carbon that are 100,000 times smaller than a human hair.1
Please note, though, that even if a breathalyzer could detect THC, there is currently no acceptable cut-off limit for THC impairment. For example, most states say that you are guilty of drunk driving (or DUI) if alcohol breathalyzers show a blood alcohol content (BAC) of .08%. Though to the disappointment of many lawmakers, states have not settled on a similar quantifiable number for marijuana use THC impairment.
Police officers first try to detect marijuana impairment via observations and field sobriety tests.
A few signs that you are under the influence of marijuana, or controlled substances include:
Most states then say that if officers have probable cause to believe you are under the influence from smoking marijuana (or using edibles), they can ask you to submit to a:
Note, though, you can refuse these tests. The most common refusal is a blood test refusal.
Most states say that a blood test refusal is illegal and can lead to an automatic driver’s license suspension for up to one year.2
Though while a refusal is illegal, most states say that there are certain situations where police can require you to submit to a blood test (for example, when police have a warrant for the test).
Authorities can use a drug recognition expert (DRE) to help determine if you are driving while high.
A DRE is a law enforcement officer with special training. The special training helps the officer identify when you are under the influence of a controlled substance.
Note that not all counties have DREs. So, if you are suspected of DUID, you may or may not be subject to a DRE evaluation.
Many states have legalized the recreational use of marijuana and have recognized the value of legalizing medicinal marijuana use.
Despite this legalization, though, it is still a criminal offense to drive while impaired by marijuana.
Law enforcement can legally stop you for driving under the influence of weed when they have probable cause that you are driving while high.
Acts that might give rise to probable cause include you:
If police stop you for driving high without probable cause, then a judge might dismiss your DUI case or reduce the charges.
Most states say that a prosecutor must successfully prove the following elements to show that you are guilty of driving under the influence of drugs:
Prosecutors can try and show that you were “under the influence” of marijuana by using any of the following evidence:
For more discussion, see our page on How long does marijuana show up in a DUI blood test?
A former Los Angeles prosecutor, attorney Neil Shouse graduated with honors from UC Berkeley and Harvard Law School (and completed additional graduate studies at MIT). He has been featured on CNN, Good Morning America, Dr Phil, The Today Show and Court TV. Mr Shouse has been recognized by the National Trial Lawyers as one of the Top 100 Criminal and Top 100 Civil Attorneys.