A drug DUI arrest can feel confusing—especially if you weren’t “high,” you took medication as prescribed, or you used cannabis hours earlier and believed you were safe to drive. In California, drug DUI charges are often built on subjective observations and testing evidence that doesn’t work like alcohol testing. That means drug DUI cases can be defensible when the stop is questionable, the officer’s conclusions are unsupported, or the testing can’t reliably prove impairment at the time of driving.
This page covers Vehicle Code 23152(f)—driving under the influence of drugs. If your case also involves alcohol, see our combined-drugs-and-alcohol page. If your arrest involved an accident, injury, refusal, or underage allegations, those also require different strategies and higher-stakes planning.
If You Were Arrested for Drug DUI in Southern California
If you were arrested for drug DUI in Southern California, the right defense usually starts by answering three core questions. First, was the traffic stop legal in the first place—meaning did the officer have a valid, lawful reason to pull you over? Second, did the police have a lawful basis to escalate the encounter into a DUI investigation and ultimately make an arrest? Third, even if the stop and arrest were lawful, can the evidence the state relies on actually prove impairment beyond a reasonable doubt, or does it fall short when you examine the facts, the timeline, and the testing methods?
This page and website provide general information in plain English, not legal advice. Laws and local court/DMV practices vary and can change, so don’t rely on this content for your case—talk to a qualified attorney promptly to review your specific facts, especially if you face charges, a DMV action, or a deadline. In many cases, you’re fighting two battles at once: the DMV process and the criminal court case.
What Is a Drug DUI in California?
A drug DUI in California is typically charged under Vehicle Code 23152(f). In plain terms, the allegation is that you drove a vehicle while under the influence of a drug to a degree that affected your ability to drive safely.
In a drug DUI case, “drugs” can mean many different substances. It may involve marijuana or THC, prescription medications such as sleep aids, anti-anxiety medications, pain medications, or stimulants, and even over-the-counter medications if they cause impairment. It can also involve illegal controlled substances, or a combination of substances that the officer believes impacted your driving.
Importantly, a drug DUI is not limited to illegal drugs. People can be arrested for drug DUI after taking medication exactly as prescribed if the officer claims it impaired driving.
Common Causes of Drug DUI Arrests
Drug DUI arrests often start with one of these triggers:
1) A traffic stop after “driving pattern” allegations: Weaving within a lane, slow driving, wide turns, delayed responses—these can be caused by many non-drug factors (fatigue, distraction, anxiety, medical issues).
2) An accident or near-miss: After a crash, officers may look for impairment explanations quickly. Stress and injury can mimic impairment symptoms.
3) A “drug cue” inside the vehicle: Smell of cannabis, paraphernalia, or admissions like “I smoked earlier.” These cues often shape the officer’s interpretation of everything that happens next.
4) A DUI checkpoint: Some checkpoints expand into drug DUI investigations when an officer believes a driver appears impaired.
Evidence in Drug DUI Cases
Drug DUI cases typically involve a mix of observations, testing, and documentation rather than a single “number” that decides the case. The evidence often includes bodycam and dashcam footage, along with the officer’s narrative about things like speech, eyes, coordination, mood, or behavior. Many cases also include field sobriety tests (FSTs), and if a Drug Recognition Expert was involved, DRE evaluation notes may become a major part of what the prosecution relies on.
Testing evidence is common as well. Blood test results are frequently used, and urine test results sometimes appear depending on the agency and the circumstances. Prosecutors may also rely on statements or admissions—such as “I took a pill,” “I smoked earlier,” or “I’m on medication”—and they may try to frame certain medical or personal factors as “impairment” evidence, even when those issues could have unrelated explanations, like fatigue, injuries, or neurological conditions.
A strong defense usually starts by demanding and analyzing the full evidence packet, including the video and the lab documentation—not just the arrest report summary.
The DRE Evaluation: What It Is and How It’s Challenged
In many drug DUI cases, officers use a Drug Recognition Expert (DRE) to conduct a structured evaluation designed to support an impairment claim. The process can include eye-related exams such as tracking and pupil size under different lighting, along with pulse and blood pressure checks. It may also involve divided-attention tasks similar to field sobriety tests, plus observations about muscle tone, balance, and overall behavior. Based on those steps, the DRE may give an opinion about whether impairment is present and, if so, which drug category or categories may be involved.
Why DRE Evidence Is Vulnerable
Even when a DRE follows the protocol, the evaluation can still be challenged because many of the “signs” officers point to are not unique to drug impairment. Symptoms like slow responses, poor coordination, or unusual eye appearance can overlap with fatigue, anxiety, injuries, medical conditions, or normal human variation—especially in a high-stress encounter. The testing environment itself can also skew results because it’s unfamiliar, pressured, and often conducted late at night or after a long roadside detention.
DRE conclusions can also be vulnerable because they depend heavily on interpretation. Officers may read ambiguous behavior in the most incriminating way, and the written narrative may not match what the video actually shows. In some cases, the evaluation lacks a solid foundation, is applied inconsistently, or is missing key documentation that would allow the defense to verify what was done and how the conclusions were reached.
A drug DUI lawyer looks closely at whether the DRE conclusions are supported by concrete facts—or whether they amount to an opinion built on assumptions.
What the Prosecutor Must Prove Under VC 23152(f)
While the exact jury instructions and case posture can vary, prosecutors generally try to prove three core points in a VC 23152(f) case. First, they must show you drove a vehicle. Second, they must show that, at the time of driving, you were under the influence of a drug. Third, they must show the drug actually affected your ability to drive with the caution of a sober person using ordinary care.
That third point is where many defenses live. In a lot of drug DUI cases, the evidence may show only that a substance was present in the body, or that an officer suspected impairment—but suspicion is not proof. A strong defense focuses on whether the state can truly connect the alleged drug use to actual impairment at the time of driving, beyond a reasonable doubt.
How Drug DUI Differs From Alcohol DUI
Most people assume the DUI is “one case.” In reality, you may be dealing with:
Alcohol DUI Usually Revolves Around a Number
n alcohol DUI cases, prosecutors often focus on a specific BAC number—typically 0.08%—and then use breath or blood test results to support the charge. They may argue that the chemical test alone “proves” the case, and they often tie that number to officer observations, field sobriety tests, and the overall narrative in the police report. In practice, the BAC result can become the centerpiece of the case, even though alcohol testing is not infallible and the details still matter—how the stop happened, what the officer actually observed, whether procedures were followed, and whether the testing process and timeline make the result reliable and legally usable.
Drug DUI Is Usually About “Impairment,” Not a Clean Threshold
In most drug DUI cases—especially those involving THC—there is no universally accepted “per se” impairment number in California that works like BAC. As a result, prosecutors often rely more heavily on officer observations, claimed driving patterns, and field sobriety tests, and sometimes a DRE (Drug Recognition Expert) evaluation. They may also point to blood or urine tests, but those results often show only the presence of a substance and do not automatically prove impairment at the time of driving. Because the evidence in drug DUI cases can be more subjective, a drug DUI defense attorney often focuses on reasonable doubt—pressing whether the evidence actually shows impairment, or whether it amounts to suspicion without proof.
Blood Tests, Urine Tests, and Drug Testing Problems
Urine tests
Urine tests can be even more problematic when the issue is proving impairment, because urine testing often reflects prior use rather than what was happening in the body at the time of driving. In other words, a urine result may show that a substance was used at some point in the past, but it may not reliably indicate when the substance was taken, how recently it was used, or whether it was affecting the driver during the actual driving.
Because of that limitation, a strong defense may argue that urine results are better framed as historical exposure—not proof of impairment while driving. The focus then shifts back to what the officer actually observed, what the video shows, and whether the prosecution can connect any testing result to real-world impairment beyond a reasonable doubt.
Marijuana (THC) DUI: What Drivers Get Wrong
THC DUI is a major source of confusion, especially because people often assume there’s a clear rule like alcohol’s 0.08% BAC limit. Many drivers believe things like, “I waited a few hours, so I’m fine,” “I’m a regular user, so it doesn’t affect me,” or “If I’m not ‘high,’ I can’t be DUI.” Those assumptions can be misleading because THC-related DUI cases don’t typically turn on a clean, universally accepted threshold in the way alcohol cases often do.
In reality, THC DUI cases are highly fact-specific and often hinge on how the officer interpreted your behavior, how you performed on field sobriety tests, whether a DRE (Drug Recognition Expert) was used and what conclusions they claimed, and what the lab results actually show. That last point matters because lab testing may detect THC metabolites that indicate prior use, without clearly establishing impairment at the time of driving.
Defenses That Work in Drug DUI Cases
Drug DUI defense is usually about finding and attacking the weak links in the state’s case. Because many drug DUI prosecutions rely heavily on subjective observations rather than a clean “per se” number, a strong defense focuses on whether the stop, the arrest, and the claimed impairment evidence actually hold up under scrutiny.
Challenging the stop
A DUI investigation often begins with the traffic stop, and the officer must have a valid legal reason to pull you over. If the stop was based on a hunch, assumption, or an articulated reason that doesn’t match the facts, your lawyer may challenge the evidence gathered afterward as the product of an unlawful stop.
Challenging probable cause to arrest
Even if the stop itself was legal, police still need a lawful basis to arrest you for DUI. In drug DUI cases, the arrest is sometimes built on vague observations and conclusions that are difficult to verify, such as “confusion,” “odd behavior,” or “slow responses.” A defense may focus on whether those claims actually add up to probable cause or whether the arrest was based more on assumptions than objective facts.
Attacking subjective impairment claims with video
Bodycam and dashcam footage can be some of the most powerful evidence in a drug DUI case, especially when it contradicts what was written in the police report. Video may show normal speech, clear responses, steady movement, or calm behavior that conflicts with claims like “slurred speech,” “couldn’t follow instructions,” or “was unsteady.” When the video doesn’t match the narrative, it can create meaningful reasonable doubt.
Field sobriety test weaknesses
Field sobriety tests are not drug-specific, and performance can be affected by many non-drug factors such as stress, fatigue, injuries, balance issues, footwear, lighting, surface conditions, and unclear instructions. A defense often challenges whether the tests were properly administered and whether the conclusions drawn from them are reliable.
Related page: /practice/dui-dwi/field-sobriety-tests/
DRE protocol challenges
If a Drug Recognition Expert (DRE) was involved, the defense can closely examine the foundation of the DRE opinion. That includes training and experience, whether the evaluation followed protocol, whether observations were consistently documented, and whether the conclusions logically follow from what was actually observed—particularly when the video tells a different story.
Lab testing and chain-of-custody issues
Drug testing is not immune from error, and lab evidence can be challenged on handling, documentation, preservation, and methodology. Chain-of-custody gaps, storage issues, incomplete records, or questionable procedures can all undermine reliability. Even when a substance is detected, the defense may argue that the result does not prove impairment at the time of driving.
Related page: /practice/dui-dwi/blood-test-errors/
Alternative explanations for “impairment”
Many conditions can mimic what officers attribute to drug impairment, including fatigue, anxiety, concussion, illness, or other medical or neurological issues. A strong defense highlights these alternative explanations and presses whether the state can truly rule them out with real evidence, not assumptions.
The goal is to show the prosecution cannot prove impairment beyond a reasonable doubt.
Common Defense Angles in THC DUI Cases
A strong THC DUI defense often starts by attacking the foundation of the stop and the impairment narrative. That can include arguing there was no bad driving and the stop was weak or pretextual, or showing the video doesn’t match the officer’s claimed “impairment” indicators. It may also involve challenging field sobriety tests based on flawed conditions or unclear instructions, and pushing back on lab results that show presence but don’t prove impairment at the time of driving. In many cases, the defense also presents alternate explanations—such as fatigue, anxiety, or medical conditions—that can look like “impairment” but have nothing to do with THC.
If cannabis is central to your case, you want a defense strategy built on evidence and timelines—not assumptions.
Prescription Medication DUI: Common Scenarios
Prescription-related drug DUI arrests often happen in situations where the driver took medication legally, but an officer claims the medication affected driving. Common scenarios include taking a sleep medication the night before and still feeling residual effects, taking an anti-anxiety medication and feeling calm but being described as “slow,” using pain medication and appearing drowsy, or combining medications—each lawfully prescribed—only to experience unexpected side effects. In these cases, the arrest often hinges less on a clear measurement and more on how the officer interpreted what they saw in the moment.
Why Prescription Drug DUI Cases Can Be Defensible
Prescription drug DUI cases can be defensible because proper use does not automatically equal impairment, and side effects vary widely from person to person. What an officer labels as “impairment” may be a misinterpretation of normal behavior, fatigue, a medical condition, or a medication effect that does not actually make a person unsafe to drive. Testing also has limits: blood and urine results may show the presence of a medication, but they don’t measure impairment the way BAC is used in alcohol cases, and they often don’t establish what—if anything—the substance was doing at the time of driving.
Your defense may involve presenting a lawful explanation, challenging the stop and arrest, and pressing the core issue: whether the state can actually prove impairment at the time of driving beyond a reasonable doubt.
DMV and License Consequences in Drug DUI Cases
Depending on the circumstances, a drug DUI arrest can trigger DMV consequences, including a license suspension action that runs on a separate track from the criminal court case. The DMV process can move quickly, and the deadlines to protect your driving privileges may be short, which is why it’s important to identify early what paperwork you were served and what deadlines apply to your situation.
Related pages: /practice/dui-dwi/dmv-hearing/ • /practice/dui-dwi/dui-license-suspension/
A DUI defense lawyer may help by evaluating whether a DMV hearing request applies to your facts and whether requesting a hearing can delay or prevent an automatic suspension. They can also prepare a strategy to challenge the DMV case using the available evidence and timelines, and coordinate the DMV defense with the court defense so the approach in one forum doesn’t undermine the other.
Penalties for Drug DUI (Overview)
Penalties for a drug DUI depend on your prior record, the specific facts of the stop and arrest, and whether any enhancements apply—such as an accident, an injury allegation, or minors in the car. Even a first-time drug DUI can carry serious consequences, including probation terms, fines and penalty assessments, required classes, and driver’s license consequences that may begin quickly through the DMV process.
Because drug DUI cases vary so widely from county to county and from courtroom to courtroom, a meaningful assessment usually requires more than a quick summary. For a tailored analysis, a DUI lawyer will typically review the police report, any bodycam or dashcam footage, and the testing evidence, then evaluate how the local court and prosecutor’s office tend to handle similar cases.
Related page: /practice/dui-dwi/dui-penalties/
What to Do After a Drug DUI Arrest
If your arrest is recent, taking the right steps early can make a real difference—especially for DMV deadlines and preserving evidence before it disappears. One of the most important moves is to speak with a drug DUI attorney quickly, because early planning helps protect your license options and ensures the right records and video requests are made as soon as possible.
It also helps to write down your medication and timeline while it’s still fresh. That includes what you took, when you took it, when you drove, when the stop occurred, and when any testing happened, because drug DUI cases often turn on timing and context. If prescriptions are involved, preserve proof early by saving photos of prescription labels, pharmacy records, and dosing instructions, since proper use and dosage details can matter.
At the same time, avoid explaining the case to police or others. Even casual statements can be misinterpreted or repeated out of context, so it’s better to let your attorney guide what should and shouldn’t be said. Finally, gather relevant medical context early if a medical condition could explain symptoms the officer attributed to “impairment,” because documentation created closer in time to the arrest can be more persuasive than trying to reconstruct it later.
Drug DUI Frequently Asked Questions
Can I get a drug DUI if the drug is legal or prescribed?
Yes. The charge focuses on alleged impairment, not whether the drug is legal.
Does a positive THC test mean I was impaired?
Not necessarily. THC testing raises complex timing and interpretation issues, which is why these cases often require careful defense review.
Will a blood test automatically convict me?
No. Lab evidence can be challenged, and presence does not always equal impairment at the time of driving.
What if I told the officer I used marijuana earlier?
Admissions can be used against you, but they don’t automatically prove impairment at the time of driving. The defense focuses on what the evidence truly proves.