Having a valid medical marijuana recommendation does not give a person the legal right to drive while impaired by cannabis. However, lawful marijuana use and driving under the influence are two different issues, and the prosecution must still prove that the driver was actually under the influence at the time of driving.
Does Medical Marijuana Make It Legal to Drive After Using Cannabis?
No.
California law prohibits driving while under the influence of any drug, including marijuana. That rule applies whether the cannabis was used recreationally or for a medical purpose.
A physician’s recommendation for medical cannabis therefore does not provide an automatic defense to a marijuana DUI charge.
But that does not mean that lawful marijuana use automatically establishes DUI.
The Prosecution Still Has to Prove Impairment
The important question in a marijuana DUI case is not simply whether the driver had used cannabis.
The prosecution must prove beyond a reasonable doubt that the driver was under the influence while driving.
Unlike alcohol DUI cases, California does not establish marijuana impairment based on a specific numerical THC concentration comparable to the 0.08% BAC standard for alcohol.
A positive blood test showing THC therefore does not, by itself, answer the question of whether the driver was impaired.
Why Medical Marijuana Use Can Complicate a DUI Investigation
A person who lawfully uses cannabis for medical purposes may have THC or cannabis-related compounds detected in a blood sample.
That evidence can become part of a DUI investigation, but interpreting it is more complicated than interpreting a blood alcohol concentration.
In addition to chemical-test results, prosecutors may rely on evidence such as:
- The driver’s driving pattern
- Officer observations
- Statements about recent cannabis use
- Field sobriety test performance
- Drug recognition evaluation findings
- The timing of marijuana use
- The circumstances surrounding the traffic stop or accident
Each piece of evidence should be evaluated in the context of the entire case.
Does a Positive THC Test Prove You Were Impaired?
No.
THC does not have the same predictable relationship between blood concentration and impairment that exists between alcohol concentration and alcohol-related impairment.
There is no California law stating that a particular THC concentration automatically makes a driver legally impaired.
This distinction can be especially important when someone regularly uses cannabis for a medical purpose.
The presence of THC may establish prior cannabis use, but the prosecution still has to connect the evidence to impairment at the time the person was driving.
Can You Still Defend a Marijuana DUI if You Use Medical Cannabis?
Yes.
A medical marijuana recommendation itself is not a defense to impaired driving, but a person accused of marijuana DUI still has the same right to challenge the prosecution’s evidence as any other defendant.
Depending on the circumstances, a defense may examine:
- Whether the traffic stop was lawful
- Whether the driver’s behavior actually indicated impairment
- Alternative explanations for physical symptoms observed by police
- The reliability and administration of field sobriety tests
- The timing of marijuana use compared with the time of driving
- The collection and handling of a blood sample
- The interpretation of THC test results
- The conclusions reached by a drug recognition evaluator
The appropriate defense depends on the evidence in the individual case.
Medical Marijuana Use Is Different From Marijuana DUI
The central distinction is straightforward: California may permit a person to lawfully use cannabis for medical purposes, but it does not permit anyone to drive while impaired by cannabis.
At the same time, evidence that a person lawfully used marijuana does not relieve the prosecution of its burden to prove DUI.
That is why the timing of use, observations of the driver, chemical testing, driving behavior, and other evidence can become particularly important in these cases.
Learn More About Marijuana DUI in California
For a more detailed explanation of THC testing, field sobriety tests, drug recognition evaluations and how marijuana impairment may be proven, read our guide to marijuana DUI laws and THC evidence in California.
If you are facing a marijuana DUI charge in Fresno or Central California, visit our Fresno marijuana DUI defense page.
Talk to a Fresno Marijuana DUI Attorney
If you have been arrested for marijuana DUI, the fact that you legally use cannabis for medical purposes does not automatically resolve the case in either direction. The prosecution’s evidence of actual impairment still matters.
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.