You take cold medicine for a bad cough. You take a medication your doctor prescribed. You use marijuana, which is legal in California. Or you use an illegal drug. Every one of those can expose you to a DUI, because California’s drugged-driving law does not care whether the substance is legal, prescribed, or bought at a pharmacy. It cares about one thing: whether the drug impaired your ability to drive.
This article explains how drug DUIs work, what they cost, and why the science is where these cases are won and lost.
DUI And Drugs: The Short Answer
California Vehicle Code section 23152(f) makes it illegal to drive under the influence of any drug that impairs your ability to drive safely. “Drug” is defined broadly and reaches far beyond illegal narcotics. It includes marijuana, prescription medications, and over-the- counter drugs, and it is not a defense that you were legally entitled to use the substance. A separate provision, section 23152(g), covers driving under the combined influence of alcohol and a drug, which can produce a DUI even when the alcohol alone was below the limit.
The defining feature of a drug DUI is what it lacks: a per se blood limit. Unlike drug DUI, alcohol law includes separate per se offense for driving with a blood-alcohol concentration of 0.08 percent or more by weight. Drug DUI has no equivalent numerical threshold; the prosecution must prove that the drug actually impaired driving at the time.
What Must The Prosecution Prove In A Drug DUI?
To prove a drug DUI under California Vehicle Code section 2315(f), the prosecution must prove that the person drove and was under the influence of a drug a the time of driving, meaning impaired to an illegal degree. A positive drug test alone, however, does not establish that element.
Any Drug, Legal Or Not: What The Law Actually Covers
The single most common misunderstanding about drug DUIs is that they are about illegal drugs. They are not. The law reaches any substance that impairs driving, and the categories that catch people by surprise are the legal ones.
| Category | Examples | The Trap |
|---|---|---|
| Illegal Drugs | Cocaine, methamphetamine, heroin, MDMA, LSD | Straightforward coverage; presence plus impairment |
| Marijuana | Recreational or medical cannabis | Legal to use, illegal to drive impaired; a dispensary receipt is no defense |
| Prescription Medication | Opioids, benzodiazepines, sleep aids, ADHD medication | A valid prescription is not a defense if the drug impaired driving |
| Over-The-Counter Medication | Antihistamines, cold and cough medicines, sleep aids | Ordinary drugstore products can support a charge |
| Combinations | Alcohol plus any drug (§ 23152(g)) | Can convict even where alcohol alone was under 0.08 |
Being legally entitled to use a drug, whether it is a prescription, a cold medicine, or legal cannabis, is not a defense to driving while impaired by it. The legality of the substance and the legality of the driving are two separate questions.
Marijuana: Legal To Use, Illegal To Drive Impaired, & Scientifically Hard To Prove
Marijuana deserves its own treatment, because it is the most common drug DUI and the one where the science most favors a knowledgeable defense.
Proposition 64 legalized recreational cannabis, but it did not touch the DUI laws. Driving under the influence of marijuana remains illegal under section 23152(f). The problem for the prosecution is that proving marijuana impairment is genuinely difficult, for reasons rooted in how the body processes THC.
There Is No Per Se THC limit, And California Rejected One On Purpose Lawmakers considered setting a blood-THC threshold like the 0.08 alcohol limit and declined, because the science does not support it. The correlation between blood THC concentration and actual impairment is generally unreliable.
THC Does Not Behave Like Alcohol In The Blood Alcohol concentration rises and falls in a reasonably predictable curve that tracks impairment. THC does not. Blood THC can spike shortly after use and then drop quickly even as subjective effects continue, so the number measured at a blood draw hours after driving may bear little relationship to impairment at the wheel.
Chronic Users Carry THC While Sober THC is fat-soluble and can remain detectable in the blood for days or even weeks after use. A daily or regular cannabis user can have an elevated blood THC level while completely sober and unimpaired, which means a “high” test result can reflect a habit rather than present intoxication.
Put those together and the marijuana DUI blood test proves far less than it appears to. A number that does not track impairment, measured after driving, in a body that may carry THC for days, is not proof of impairment at the time of driving. That gap is exactly where the case below was won.
A Past Marijuana DUI Case At Vijay Law
In a past marijuana DUI case at Vijay Law looked bad on paper for our client. The officer reported that the car smelled of marijuana. Our client had a high THC test result. His eyes were red and bloodshot, and he performed poorly on the field sobriety tests. A jury could have easily convicted on those facts alone.
The case proceeded to trial because the science of marijuana DUIs makes it very difficult to prove. We put on expert testimony explaining the timing problem, that the moment of ingestion, the moment of peak effect, and the moment of driving are three different times, and that a THC number from a later blood draw does not establish impairment at the earlier moment of driving. THC does not track impairment the way alcohol does, and a high number does not answer the question the jury had to answer.
Our expert also testified that experienced, regular marijuana users do not necessarily differ in measurable ways from non-users on some of the simulated roadside tests, because tolerance changes how the drug affects performance. The poor field sobriety performance, with no baseline performance, was far weaker evidence than it seemed.
The jury acquitted. Despite the smell, the high test result, the red eyes, and the poor field sobriety tests, they could not find beyond a reasonable doubt that our client was under the influence of marijuana at the time he was driving. The evidence proved he had used cannabis but it did not prove he was impaired at the wheel, and those are not the same thing.
Why Field Sobriety Tests And DREs Are Weaker Than They Look
Two pillars of the prosecution’s drug DUI case are more vulnerable than most people assume.
Field sobriety tests were built for alcohol. The standardized field sobriety tests were designed and validated to detect alcohol impairment, not drug impairment. Their application to drugs, and especially to marijuana, rests on far weaker scientific footing, which means poor performance is weaker evidence in a drug case than in an alcohol case.
The Drug Recognition Expert is a trained officer, not a scientist. When drugs are suspected, the prosecution often relies on a Drug Recognition Expert, an officer trained in a twelve-step evaluation protocol to identify drug impairment. That evaluation can be challenged. The DRE is a police officer, not a physician or toxicologist, the protocol’s reliability is contested, and where no DRE was involved at all, an officer’s lay testimony about drug impairment may be subject to a motion to limit or exclude it. These are technical challenges, and they are often decisive.
The Consequences: Criminal, DMV, Job, And Immigration
A drug DUI carries the same architecture of consequences as an alcohol DUI, with a few important differences.
Criminal penalties. A first drug DUI is generally a misdemeanor with penalties comparable to a first alcohol DUI, jail exposure, fines, a DUI program, and probation, and it escalates with priors on the same ten-year scale, which we cover in our article on repeat DUIs. Drug DUIs and alcohol DUIs count as priors for each other.
The DMV difference. The DMV’s administrative per se suspension is based on blood alcohol. In a pure drug DUI with no alcohol involved, there may be no administrative suspension at the arrest stage, and a suspension notice issued at arrest can be set aside once testing shows no alcohol. But a conviction under section 23152(f) still triggers its own license suspension. However, a refusal or failure to complete a required chemical test can trigger a separate DMV suspension or revocation even where drugs are alleged. We explain the administrative process in our article on DMV hearings.
Employment. A drug DUI is a misdemeanor conviction with the same employment and professional-licensing exposure as an alcohol DUI, and for licensed professionals a drug- related offense can raise the same substance-related concerns. We cover this in our article on DUI and employment.
Immigration. For non-citizens, a drug DUI can be more dangerous than an alcohol DUI, because anything touching controlled substances can be treated harshly in immigration law, and a drug-related offense can raise grounds that a simple alcohol DUI does not. We address this in our article on DUI and immigration. A non-citizen facing any drug DUI should involve immigration counsel early.
What To Do With A Drug DUI Charge
The steps mirror an alcohol DUI, with an added emphasis on the science. Preserve the DMV hearing within ten days if there is any alcohol allegation, and get advice on the administrative posture if the case is drug-only. Say nothing to investigators, and be aware that a DRE evaluation is an interrogation as much as an examination. Keep in mind that while you need not participate in a DRE, you can’t refuse to submit to a chemical blood test following a lawful arrest. Do retain a lawyer who understands the toxicology, because a drug DUI, more than almost any other, turns on the science of impairment rather than a number, and the defense depends on the ability to challenge that science with expert support. We explain the full range of DUI defenses in our article on how DUI cases are won.
Frequently Asked Questions About Drug DUIs
Can I Get A DUI From Prescription Or Over-The-Counter Medication?
Yes. California’s drug DUI law covers any drug that impairs driving, including prescriptions and over-the-counter medicines like antihistamines and cold medicine. A valid prescription or a legal purchase is not a defense if the drug impaired your ability to drive.
Is There A Legal Limit For Marijuana Like There Is For Alcohol?
No. California has no per se THC limit and deliberately declined to set one, because blood THC levels do not reliably indicate impairment. The prosecution must prove you were actually impaired at the time of driving, not just that THC was present.
Can I Be Convicted If I Have A Medical Marijuana Card?
Yes. Legal use, medical or recreational, is not a defense to driving while impaired by marijuana. The legality of using the drug and the legality of driving under its influence are separate questions.
Why Are Marijuana DUIs Hard To Prove?
Because THC does not behave like alcohol. Blood THC can be high shortly after use and drop quickly, chronic users carry THC while sober, and the number measured after driving may not reflect impairment at the wheel. This scientific gap is the core of the defense.
Does A Drug DUI Suspend My License Through The DMV?
If there is no alcohol involved, there may be no administrative per se suspension at arrest, because that action is alcohol-based. But a conviction for a drug DUI still triggers a license suspension. The route to the suspension is different, but the license is still at stake.
Do I Need A Lawyer Who Understands The Science?
For a drug DUI, especially marijuana, yes. These cases turn on toxicology, pharmacology, and the reliability of field sobriety tests and DRE evaluations far more than on a single number, and challenging that evidence requires real command of the science.
This article provides general information and is not legal advice. Every case turns on its own facts. If you are facing a drug DUI, consult experienced counsel, and act within ten days to protect your license if any alcohol is alleged.