Marijuana, a frequently encountered substance in driving under the influence (DUI) arrests, has raised unique challenges with its legalization for medicinal and recreational use in California.  While some may underestimate the seriousness of driving under its influence, the state maintains a strict stance against impaired driving due to marijuana use, implementing stringent measures to keep such drivers off the roads and impose penalties accordingly.  

The psychoactive component of marijuana, responsible for its euphoric effects, is THC (Delta-9-tetrahydrocannabinol).  Regular marijuana users often have THC in their systems, even without an active high.  This presence of THC will show up in a blood test taken after a person has been arrested for DUI.  However, it does not prove that the user was "high" at the exact time of driving.  

Studies show that THC can remain detectable in your system for up to 30 days, even though the initial high lasts only a few hours. The California Office of Traffic Safety (OTS) warns that driving immediately after marijuana use can increase crash risks by 25 to 35%, as its impairing effects set in rapidly.  However, these effects can be delayed when marijuana is ingested rather than smoked.

Even if you use marijuana for medical reasons under a doctor's care, the effects of THC still apply, making it illegal to drive if your ability to safely operate a motor vehicle is impaired.  THC is a potent psychoactive compound, and its influence can lead to:

• Euphoria
• Heightened sensory experiences
• Memory problems
• Impaired judgment
• Slower reaction times
• Issues with balance, coordination, and motor skills

Clearly, these effects impair your ability to drive safely. Thus, even if you have a medical marijuana prescription, it does not exempt you from legal consequences when it comes to impaired driving.

Law enforcement cannot stop you without a valid reason.  An officer must observe behaviors indicating impaired or intoxicated driving to initiate an arrest and testing.

Behaviors that might arouse suspicion include:

• Swerving or weaving between lanes
• Collisions with other vehicles
• Disregarding traffic signals (stop signs and lights)
• Excessive speeding or driving too slowly
• Once pulled over, other signs of impairment may become evident. For instance, the presence of marijuana odor in your vehicle, drowsiness, slow or slurred speech, and red or watery eyes can contribute to an arrest.

Following an arrest for suspicion of DUI, and the officers suspect you are under the influence of drugs, per California's implied consent law you will be required to submit to a blood or urine test.  The sample will be tested for THC.  However, this test cannot determine when you last consumed marijuana.  Unlike alcohol, which has a legal limit threshold (0.08% BAC) in California, there is no equivalent for THC levels. THC levels alone do not conclusively establish impairment.