Driving Under the Influence of Marijuana

Often referred to as “DUI marijuana”, “marijuana DUI”, “driving stoned” or “drugged driving”, driving under the influence of marijuana — like driving under the influence of alcohol — is a criminal offense in California. Even if the marijuana used is "medical marijuana”, or if recreational marijuana is eventually legalized in California, driving while impaired by from its use remains a crime.

The applicable statute, California Vehicle Code section 23152, became effective as of January 1, 2014, and reads in relevant part as follows:

V.C. sec. 23152(e) — It is unlawful for a person who is under the influence of any drug to drive a vehicle.

The term “drug” includes cannabis, or marijuana (sometimes called “grass” or “weed”). The statute goes on to include driving under the influence of a combination of alcohol and marijuana:

V.C. sec. 23152(f) — It is unlawful for a person who is under the combined influence of any alcoholic beverage and drug to drive a vehicle.

If a first offense, the penalties for marijuana DUI are the same as for driving under the influence of alcohol, and generally consist of:

  • Up to 6 months imprisonment in county jail
  • Fine (including fees and assessments) from $1800 - $2000
  • Driver’s license suspension for 6 months (restricted license possible after 30 days)
  • DUI school for 3, 6 or 9 months
  • "Summary" (informal) probation for 3 or 5 years

If probation is not granted, a jail sentence of between 96 hours and 6 months will be imposed.

Elements of the Offense

The offense of DUI marijuana requires proof beyond a reasonable doubt of two elements:

  • Driving a motor vehicle
  • While under the influence of marijuana

Driving is usually proven through the testimony of the officer who observed the driving. However, in cases where the officer was not present, such as where there has been an accident or the car is parked, the driving element may be established through the testimony of passengers, witnesses, statements of the defendant, or — in some cases — through circumstantial evidence. This circumstantial evidence of driving under the influence of marijuana can consist of testimony that, for example, the defendant was seen behind the wheel of the parked car, the engine was warm, the keys were in the defendant’s pocket, etc. Circumstantial evidence is, of course, usually more susceptible to reasonable doubt in court than is direct evidence.

The second element in a marijuana DUI case — the defendant was under the influence of marijuana while he was driving — requires proof of impairment, This is legally defined as being impaired to such an extent that he lacked the “ability to drive with the caution characteristic of a sober person of ordinary prudence under the same or similar circumstances.” This is, of course, a notoriously vague and subjective standard of proof.

Does Marijuana Cause Impairment?

Does marijuana in fact cause impairment of driving ability? There is substantial evidence that it does not. A review conducted in 2002 of seven separate studies of over 7,000 drivers involved in auto accidents concluded that, “Crash culpability studies have failed to demonstrate that drivers with cannabinoids in the blood are significantly more likely than drug-free drivers to be culpable in road crashes”.

Two separate studies conducted by the U.S. Department of Transportation have reached similar conclusions. In one, researchers concluded that "although alcohol was found consistently and significantly to cause impairment, marijuana had only an occasional effect". In the other study, researchers found that “THC is not a profoundly impairing drug…It apparently affects controlled information processing in a variety of laboratory tests, but not to the extent which is beyond the individual’s ability to control when he is motivated and permitted to so so in driving.” See “Does Marijuana Affect Driving Ability?"

Proving Impairment

The usual means of poving the required degree of impairment in a DUI marijuana case is through (1) such observations by the investigating officer as erratic driving, physical appearance, mental acuity, field sobriety tests, the presence of marijuana or paraphernalia in the car, and incriminating statements, and (2) analysis of the driver’s blood for THC (Tetrahedroncannabinol).

An increasingly common practice in DUI marijuana investigations is to call in a "drug recognition expert”, also called a “drug recognition evaluator” (DRE) — at the scene of the investigation or later at the police station or medical facility. This is an officer who has gone through a training program, originally created by the Los Angeles Police Department in the 1970s and later adopted by state and federal law enforecment agencies nationwide. The program involves the use of a standardized DRE drug impairment protocol of observations and tests for the recognition of drug influence and impairment, including impariment caused by marijuana. The protocols have, however, been the subject of criticism, and the training, skills and abilities of individual DREs vary widely. In the end, the test is necessarily somewhat subjective and dependent upon the training, experience and accuracy of the officer.

The Blood Test

A driver who is arrested for driving under the influence is required by law to submit to breath or blood testing; refusal to do so can be punished by an increased jail term and a longer license suspension. Since marijuana cannot be detected on a breathalyzer, drivers suspected of DUI marijuana are required to submit to having a sample of blood drawn. The blood is then later tested by a laboratory for the presence of THC.

There are, however, periodic attempts to develop and use roadside tests for marijuana, just as hand-held breath alcohol tests were developed in recent years. The most recent of these DUI marijuana roadside tests have involved the investigating officer taking a swab of saliva from the driver’s mouth, and then using a device at the scene of the investigation to analyze the saliva for THC. And there are recurrent attempts to enact legislation in Sacramento to authorize this procedure. To date, these attempts have been unsuccessful. See, for example, “Roadside Oral Swab Tests Coming?"

The problem with testing the blood for marijuana or saliva, however, is simple: analysis can only determine the presence of THC in the blood — it cannot determine either (1) when it was consumed, or (2) whether the amount would have caused any impairment. Inactive elements of marijuana can stay in a person’s blood for days, even weeks — long past when it could have any effects on the driver. And it has never been conclusively clearly established how much marijuana can cause driving impairment — if it causes any impairment at all.

In other words, it is difficult to establish any connection between the THC in the blood sample and the degree of driving impairment (if any).


There are basically three defenses to a charge of driving under the influence of marijuana in California:

  1. The defendant was not driving.
  2. The defendant did not use marijuana.
  3. The defendant used marijuana but was not impaired at the time of driving.
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