In California, it is illegal to operate a motor vehicle under the influence of any substance, lawfully possessed or not, if the substance used causes physical or mental impairment that makes a person unable to drive safely. Most commonly, California DUI statutes are applied to those driving under the influence of alcohol but not exclusively.

Driving Under the Influence (DUI) (California Vehicle Code §23152(a)

In California, it is illegal to operate a motor vehicle under the influence of any substance, lawfully possessed or not, if the substance used causes physical or mental impairment that makes a person unable to drive safely. Most commonly, California DUI statutes are applied to those driving under the influence of alcohol but not exclusively. The law covers all controlled substances, including marijuana, as well as, contrary to some common misconceptions, perfectly lawful substances such as a long list of prescription drugs available on the market today. Medical marijuana users must be aware that they are not exempt from DUI laws by reason of their medical status.

In California, first time DUI offense prosecuted under §23152(a) is a misdemeanor punishable by maximum of 6 months in county jail, a fine between $390 and $1,000, mandatory alcohol program, suspended or restricted license and 3 year probation. If the prosecution involves a person under 21, conviction will result in 1 year license suspension. If the impaired driving results in bodily injury or death, even the first time offense can be prosecuted as a felony punishable by imprisonment in state prison.

Defending Marijuana Related DUI. A skilled lawyer often has an easier task defending marijuana related DUI cases than cases where alcohol is involved. In drunk driving prosecution, the defendant is presumptively guilty when the blood alcohol level is 0.08 percent or more. By contrast, there is no set legal threshold - no "guilty" standard for the THC level detected in the defendant's system - for when a person is presumptively impaired when using marijuana. This lack of a bright line standard makes it more difficult for the prosecution to prove their case. In addition, an effective, diligent and knowledgeable attorney can often defend these cases successfully by relying on experts and various studies showing lack of scientific agreement on when marijuana causes impairment. Scientific and expert literature on the subject contains data that there is no impairment if the ingestion took place more than 2 to 3 hours before driving. Among the best defense tools is the government's own National Highway Traffic Safety Administration of the U.S. Department of Transportation which in 2003 published a cannabis safety study concluding that any effects from using marijuana dissipate quickly after one hour! Also potentially available, although not always advisable, is the so-called heavy user defense based on the idea that heavy use builds tolerance to impairment.

A good criminal defense lawyer will often exploit the lack of sophistication, and sometimes simple incompetence, of prosecution's testing laboratories. Test results often will reveal nothing more than the presence marijuana metabolites without having differentiated between various kinds. Metabolites are byproducts created after metabolization. They might or might not be psychoactive and they are not the same as the active drug. The tests might not be able to distinguish between, for example, the highly potent 11-OH-THC metabolite and the non-psychoactive THC-COOH (carboxy THC) which is marijuana's primary metabolite and which does not cause impairment. Presence of nonactive metabolites does not indicate either impairment or recency or frequency of use.

Note, however, that presence of marijuana would not make your case easier if you also consumed alcohol, even at less than 0.08 percent blood alcohol level necessary for a conviction for alcohol related drunk driving. It has been shown, and the prosecution will most certainly argue, that using both alcohol and marijuana significantly increases potential for impairment. The simple rule is that alcohol and weed do not mix. Do not do it as you are bound to make your lawyer's job significantly more complicated.

Refusing Questions and Tests. If pulled over by the police, you have the right to refuse any questions with the exception of having to identify yourself. You may also refuse to take various field sobriety tests (walking in straight line, balancing, etc). If you refuse, make sure that you are not being confrontational towards the officer or more uncooperative than you need to be. Remain respectful. A simple statement that you have been advised to stay within your rights in these types of situations will suffice. Perhaps the most important thing to know is that you DO NOT have the right to refuse what is legally referred to as a chemical test. Refusal to take a chemical test, either breath, blood or urine, will result in the suspension of your driver's license for 1 year or more and can be used against you in the court of law as evidence of your consciousness of guilt.

Choosing the Chemical Test. Most commonly, if you are arrested, the officer will offer you to choose between a breath or blood test. If given an option, you should choose a breath test which does not measure THC levels in the blood. However, if the officer suspects you have been using drugs, or for some other reason you are requested to take either a blood or urine test, you must comply and your choice should depend on when you have used marijuana. Choose the blood test if you have not used marijuana recently because with THC will be detectable only for up to 12 hours after use. If you are a daily user or used recently, the urine test is preferable. While the urine test will show the presence of marijuana metabolites for up to 35 days, this test is much less reliable in terms of proving actual impairment at the time of driving.

Is Driving While Using Pot Safer Than Under Influence of Alcohol? Arguably, yes, because marijuana's impact on psychomotor skills is subtle and evidence of marijuana's culpability in on-road driving accidents and injuries is far less clear than in situations involving alcohol intoxication. While some studies have indicated that illicit drug use is associated with an increased risk of accident, a relationship has not been established regarding the use of psychoactive substances and crash severity. By contrast, alcohol is known to increase drivers' risk-taking behavior and is a primary contributor in on-road accidents. The risk associated with drivers who operate a vehicle above or near the legal limit for alcohol intoxication is approximately three times greater than the fatality risk associated with drivers who are under the influence of marijuana.

Although acute cannabis intoxication following smoking has been shown to mildly impair psychomotor skills, this impairment is seldom severe or long lasting. Studies have shown that marijuana's acute effects on psychomotor performance include minor impairments in tracking (eye movement control and decreased peripheral vision) and slower reaction time, as well as variation in lateral positioning, headway (drivers under the influence of cannabis tend to tailgate less), and slower speed following cannabis inhalation. In general, these variations in driving behavior are noticeably less consistent or pronounced than the impairments exhibited by subjects under the influence of alcohol. Also, unlike subjects impaired by alcohol, individuals under the influence of cannabis tend to be aware of their impairment and try to compensate for it accordingly, either by driving more cautiously or by expressing an unwillingness to drive at all. As a result, cannabis-induced variations in performance do not appear to play a significant role in on-road traffic accidents when THC levels in a driver's blood are low and/or cannabis is not consumed in combination with alcohol.

That said, drivers under the influence of illicit drugs do experience an enhanced fatality risk compared to sober drivers, and while cannabis is said by most experts to be safer with motorists than alcohol and many prescription drugs, responsible cannabis consumers should never operate motor vehicles in an impaired condition. Cruising on cannabis is not the best idea.