Marijuana may be legal for adults to use in California, but it is still illegal to drive while under the influence of cannabis. Unlike alcohol DUI cases, however, California does not use a specific THC concentration as a legal limit for marijuana DUI.
A marijuana DUI case therefore often depends on much more than whether THC was detected in a driver’s blood. Prosecutors may rely on driving behavior, officer observations, field sobriety testing, statements, chemical-test evidence, and other circumstances in an effort to prove that cannabis actually impaired the person’s ability to drive safely.
Is It Illegal to Drive After Using Marijuana in California?
California Vehicle Code section 23152(f) makes it unlawful for a person who is under the influence of any drug to drive a vehicle.
That includes marijuana.
California law also prohibits driving while under the combined influence of alcohol and a drug.
The important distinction is that using marijuana and driving under the influence of marijuana are not necessarily the same thing. The prosecution must prove impairment, not merely that a person used cannabis at some point before driving.
Is There a Legal THC Limit for Driving in California?
No.
California does not currently have a numerical THC limit comparable to the 0.08% blood alcohol concentration standard that applies to most adult drivers in alcohol DUI cases.
For alcohol, California law establishes a per se offense when a driver’s BAC reaches the statutory level.
Marijuana DUI is different. There is no California law stating that a particular number of nanograms of THC in a driver’s blood automatically establishes that the person was under the influence.
That makes the interpretation of THC evidence an important issue in many marijuana DUI cases.
Does THC in Your Blood Prove Marijuana DUI?
Not by itself.
A blood test may establish that THC or cannabis-related compounds were present in a person’s system, but the presence or concentration of THC does not necessarily establish the person’s level of driving impairment at a particular time.
THC behaves differently in the body than alcohol.
Research has found that blood THC concentration does not correlate with impairment in the same predictable manner that blood alcohol concentration does. THC levels can change rapidly after cannabis use, and the relationship between a measured THC concentration and actual driving ability can vary considerably from person to person.
For this reason, a prosecutor generally cannot rely on a THC number in the same way that prosecutors rely on a BAC of 0.08% or higher in an alcohol DUI prosecution.
How Do Prosecutors Try to Prove Marijuana DUI?
Because there is no per se THC limit, marijuana DUI cases frequently involve several different types of evidence.
Prosecutors may rely on:
- The reason for the traffic stop
- The driver’s speed or driving pattern
- An accident or other driving event
- The driver’s physical appearance and behavior
- Statements about marijuana use
- Field sobriety test performance
- Observations by the arresting officer
- Observations by a Drug Recognition Expert or Drug Recognition Evaluator
- Blood-test results
- Marijuana or cannabis products allegedly found in the vehicle
- Other evidence concerning the driver’s condition at the time of driving
The defense can examine each part of this evidence rather than assuming that a positive THC result proves impairment.
What Is a Drug Recognition Evaluation?
Law enforcement agencies may use specially trained officers in suspected drug DUI investigations.
These officers are often referred to as Drug Recognition Experts or Drug Recognition Evaluators.
A drug recognition evaluation can involve observations and tests intended to identify whether a person appears impaired and, if so, the category of drug suspected.
The officer’s conclusions are still evidence that can be examined and challenged. The underlying observations, procedures, training, consistency of the findings, and other possible explanations for the driver’s condition may all be relevant.
Are Field Sobriety Tests Reliable for Marijuana DUI?
Field sobriety tests may be used during a marijuana DUI investigation, but their significance can be disputed.
Traditional field sobriety tests were developed largely in connection with alcohol-impaired driving investigations.
Performance can also be affected by factors unrelated to drug impairment, including:
- Medical conditions
- Injuries
- Fatigue
- Anxiety or nervousness
- Uneven road surfaces
- Footwear
- Weather and lighting conditions
- How the officer explained or administered the test
The fact that an officer believes someone performed poorly on a field sobriety test does not automatically establish marijuana impairment.
How Is Marijuana DUI Different From Alcohol DUI?
One of the largest differences involves chemical testing.
In a typical alcohol DUI case, breath or blood testing can provide a BAC measurement, and California law establishes specific BAC thresholds.
Marijuana does not work the same way.
There is currently no universally accepted THC concentration that corresponds to a predictable degree of driving impairment in the way BAC does for alcohol.
A marijuana DUI case therefore tends to depend more heavily on the overall circumstances surrounding the driving and arrest.
Can Someone Be Charged With DUI After Legal Marijuana Use?
Yes.
California’s legalization of recreational marijuana did not legalize driving while impaired by marijuana.
Likewise, a person who legally uses cannabis for medical purposes can still be arrested and prosecuted if law enforcement alleges that the person’s ability to drive was impaired.
Legal possession or legal use of marijuana is therefore different from the question of whether a person was under the influence while driving.
What About Marijuana Combined With Alcohol?
California law separately prohibits driving while under the combined influence of alcohol and drugs.
A case involving both alcohol and marijuana may include:
- A breath or blood alcohol measurement
- Blood testing for THC
- Officer observations
- Field sobriety tests
- Statements regarding alcohol or marijuana consumption
- Driving behavior
The presence of both substances does not eliminate the prosecution’s burden to prove the charged offense.
The defense should evaluate the evidence concerning each substance and whether the evidence actually establishes impairment at the time the person was driving.
Can You Refuse a Chemical Test in a Marijuana DUI Investigation?
California’s chemical-testing rules can be complicated, particularly because the rules that apply before an arrest are not necessarily the same as the rules that apply after a lawful DUI arrest.
An alleged refusal to submit to or complete a required chemical test can create additional legal and driver’s-license consequences.
Whether a refusal occurred, whether the officer gave the required advisements, what type of test was requested, and whether the legal requirements for testing were satisfied can all become issues in a DUI case.
Because the consequences depend on the circumstances, drivers should not assume that the same chemical-testing rules apply in every marijuana DUI investigation.
Does a Drug-Only DUI Trigger the Same Immediate DMV Suspension as an Alcohol DUI?
Not necessarily.
California’s Administrative Per Se process is primarily associated with alcohol-related arrests involving a qualifying BAC result or a chemical-test refusal.
The California DMV distinguishes drug-only DUI cases from alcohol-related Administrative Per Se cases. In a drug-only DUI case without a qualifying alcohol-related APS basis, driver’s-license consequences generally arise following a DUI conviction rather than from the same immediate BAC-based administrative suspension that can occur in an alcohol DUI arrest.
A particular case can become more complicated when alcohol and drugs are both alleged or when there is an alleged chemical-test refusal.
Common Issues in a Marijuana DUI Defense
Defending a marijuana DUI charge can involve examining whether the evidence actually demonstrates impairment at the time of driving.
Depending on the case, issues may include:
- Whether the traffic stop was lawful
- Whether the officer’s observations actually indicate impairment
- The significance of the driver’s field sobriety test performance
- Whether statements about marijuana use were properly obtained
- The timing between driving, arrest, and blood collection
- The collection and handling of the blood sample
- The laboratory testing procedures
- The meaning of the reported THC concentration
- Alternative explanations for the driver’s appearance or behavior
- The credibility and conclusions of a drug recognition evaluation
The appropriate defense depends on the evidence in the individual case.
Why the Timing of Marijuana Use Matters
Questions about when marijuana was consumed can become important in a cannabis DUI investigation.
THC concentrations can change substantially over time, and the concentration measured when blood is drawn later does not provide a simple measurement of how impaired someone was while driving.
The method of consumption may also matter. Smoking or vaping cannabis and consuming an edible can produce different patterns of absorption and effects.
For these reasons, determining impairment from a single laboratory result can be considerably more complicated than interpreting an alcohol BAC measurement.
Can Marijuana DUI Charges Be Reduced or Dismissed?
An arrest for marijuana DUI does not automatically result in a conviction.
The prosecution still has the burden of proving the charged offense beyond a reasonable doubt.
Depending on the circumstances, weaknesses in the prosecution’s evidence may involve the reason for the traffic stop, observations of impairment, testing procedures, the interpretation of THC evidence, or whether the evidence actually connects marijuana use to impaired driving.
Some cases may be resolved through reduction or dismissal of charges, while others may proceed to trial.
Learn More About California DUI Defense
Marijuana DUI is one type of drug-related DUI prosecution in California.
For more information specifically about defending cannabis and drug DUI allegations, visit our Fresno marijuana DUI defense page.
You can also learn more about California DUI laws, BAC limits, and penalties and our broader Fresno DUI defense services.
Talk to a Fresno Marijuana DUI Attorney
If you have been arrested for driving under the influence of marijuana in Fresno or elsewhere in Central California, the evidence should be evaluated carefully rather than assuming that a positive THC test establishes guilt.
Gregory W. Fox has more than 20 years of experience defending people accused of DUI and other California criminal offenses.
Call the Law Office of Gregory W. Fox at (559) 222-5800 to request a confidential consultation.
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