Cannabis is legal for adults in California. Driving after using it is not. That gap catches a lot of people off guard. You can buy an eighth legally at a dispensary in Kearny Mesa, use it in your own home, and still get arrested for DUI on the drive home if an officer decides you were impaired.

Marijuana DUI cases work very differently from alcohol cases, and in some ways they are shakier for the prosecution. There is no simple number, no clean 0.08 line, that proves you were too high to drive. That creates real problems for the state and real opportunities for the defense. Here is how these cases actually work in California, and what to watch out for.

This article is general information, not legal advice. Every case is different, and the facts of your stop matter more than any general rule.

The Law: You Can Be Charged Even Though Cannabis Is Legal

California's DUI statute, Vehicle Code section 23152, is not limited to alcohol. Subsection (a) makes it unlawful to drive under the influence of any drug, and it treats cannabis as a drug for this purpose. So the fact that marijuana is legal to buy and use has no bearing on whether you can be charged with driving under its influence. Legal to possess does not mean legal to drive on.

The charge here is what people often call a "drug DUI" or a marijuana DUI. To convict, the prosecution has to prove that the cannabis actually impaired your ability to drive as a cautious person would under similar circumstances. That is the whole ballgame, and it is a much harder thing to prove than a breath number. Our marijuana DUI practice page goes deeper on the specifics.

There Is No Legal THC Limit in California

With alcohol, the science is settled enough that the state set a bright line at 0.08 percent for most adult drivers. Blow over that number and you can be charged under a "per se" theory, meaning the number itself is the violation.

Marijuana has no equivalent. California has not set a legal THC blood limit, and for good reason. THC does not move through the body the way alcohol does. It can linger in the blood of a regular user for days or even weeks after the high has worn off, long after any impairment is gone. A frequent user might show a THC level while stone cold sober, and an occasional user might be genuinely impaired at a lower level. The number on a blood test does not reliably tell you whether someone was actually too high to drive at the moment they were behind the wheel.

Because there is no per se limit, the prosecution cannot simply point to a lab result and rest. They have to prove actual impairment, and that is a fight worth having. Our drug DUI page explains how these no-limit cases play out.

How Police Try to Prove a Marijuana DUI

Without a magic number, the state leans on other kinds of evidence. In a typical San Diego cannabis DUI, expect to see some combination of these:

  • The officer's observations. Bloodshot or watery eyes, the smell of marijuana, slow or slurred speech, an admission that you used earlier, green residue on the tongue, the way you drove before the stop.
  • Field sobriety tests. The walk and turn, the one leg stand, and the eye tests. These were designed decades ago primarily to detect alcohol impairment, and their value for cannabis is heavily debated.
  • A Drug Recognition Expert (DRE). Some departments call in an officer with special training who runs a longer, twelve-step evaluation and offers an opinion that you were under the influence of a specific drug category. A DRE opinion sounds authoritative, but it is still an opinion, and it can be challenged.
  • A blood test. Breath tests do not detect THC, so cannabis cases usually involve a blood draw. The lab reports a THC level, but as noted, that level does not translate cleanly into impairment.

Notice what is missing from all of this: any single objective measure that ties a specific level to specific impairment at the specific time you were driving. The case is built on inference stacked on inference, and each link in that chain can be tested.

Why These Cases Are Harder for the Prosecution

The central weakness in a marijuana DUI is timing. The state has to prove you were impaired while you were driving, not an hour earlier and not that afternoon. THC blood levels usually peak quickly and then drop, and the blood draw often happens well after the stop. A rising or falling THC level, combined with the long tail of THC in regular users, makes it genuinely difficult to say what your level was, and what it meant, at the wheel.

Field sobriety tests add more doubt. Plenty of sober people perform poorly on them because of nerves, fatigue, injuries, footwear, or the simple stress of flashing lights on the shoulder of Interstate 8. Attributing a wobble on the one leg stand to cannabis, as opposed to a bad ankle and a scary night, is a leap.

Even a DRE evaluation, which prosecutors like to present as scientific, rests on subjective judgment calls. Cross-examination can expose the gaps between the checklist and reality.

Common Defenses in a Cannabis DUI

Every case is different, but the defenses that come up again and again include these:

  • No actual impairment. You may have used cannabis at some point, but the state cannot prove it affected your driving at the moment that counts.
  • THC level does not equal impairment. The blood number, standing alone, proves prior use, not impairment. For a regular user, it may prove almost nothing about that night.
  • The stop was unlawful. If the officer had no valid reason to pull you over, the evidence that followed may be suppressed. This is often the strongest angle of attack.
  • Bad field sobriety testing. Poor instructions, poor conditions, or a medical or physical explanation for the performance.
  • Blood testing problems. Chain of custody issues, contamination, improper storage, or lab error. A blood split analysis by an independent expert sometimes tells a different story.
  • Innocent explanations for the observations. Allergies and long days cause red eyes. The smell of cannabis in a car does not prove the driver was high while driving.

Penalties, and Why You Should Not Just Plead

A first marijuana DUI in California is generally charged as a misdemeanor, and the exposure looks a lot like a first alcohol DUI: fines and fees, DUI school, probation that commonly runs three to five years, and possible license consequences. In more serious cases, especially where someone was hurt, the stakes climb quickly.

Because the science is contested and the proof is thin, a marijuana DUI is often a case worth fighting rather than folding on. Pleading guilty because you assume there is no defense is a mistake I see too often. Before you decide anything, get a real evaluation of the evidence. Our related post on field sobriety tests shows just how much of this so-called proof can be picked apart.

How Crudo Law Approaches Marijuana DUI Cases

Joe Crudo treats these cases as what they are: impairment cases that the state has to prove, not automatic convictions. He digs into the blood evidence, questions whether the THC level says anything meaningful about that night, and scrutinizes the field sobriety tests and any DRE evaluation line by line. When needed, he brings in independent toxicology analysis to counter the state's expert.

Just as important, he looks at the stop itself. If the traffic stop was not lawful, or if the officer jumped to a drug conclusion without real support, that is a foundation problem for the entire case. Joe handles his cases personally, so the person reading the toxicology report and building the defense is the same person standing next to you in court. You can read more about that approach on the about page.

A Medical Card or a Legal Purchase Is Not a Defense

This is worth saying plainly, because it trips people up. Having a medical marijuana recommendation, or buying your cannabis legally from a licensed dispensary, does not protect you from a DUI charge. The law does not care whether your use was legal. It cares whether you were impaired while driving. A prescription bottle and a dispensary receipt prove the purchase was lawful, not that you were safe behind the wheel.

The same goes for the "I have a high tolerance" argument. Telling an officer, or later a jury, that you use cannabis regularly and it does not affect your driving usually does more harm than good. It confirms use and invites the assumption of impairment. What actually helps is the opposite approach: making the state prove, with real evidence tied to the moment you were driving, that cannabis impaired you. That is where these cases tend to fall apart, and it is why the defense focuses on the timing and the quality of the proof rather than on your medical paperwork.

Cannabis is legal, but a marijuana DUI charge is real, and it can follow you. The good news is that these cases are often far weaker than they first appear, precisely because there is no clean line and no easy number. That uncertainty works in your favor when you have someone who knows how to press on it.

If you have been arrested for a marijuana or cannabis DUI in San Diego, call Crudo Law at (858) 622-7280 or reach out through our contact page for a free and confidential consultation. Let's look at the actual evidence together and figure out where you really stand.