Marijuana (THC) and alcohol metabolize differently in the human body, and so the methods by which law enforcement establish “intoxication” for purposes of building a criminal case against a person accused of a marijuana DUI must be scientifically substantiated.  There are unique issues that present themselves in the case of proving whether a person is “under the influence” of marijuana.

Driving under the influence of drugs has been prosecuted for a long time now.  Vehicle Code Section 23152(f) specifically forbids the act of driving under the influence of drugs.  But with the legalization of recreational use of marijuana, there will likely be an increase in prosecutions for driving under the influence of marijuana.  With an increase marijuana DUI cases will come the need for law enforcement and the courts to establish guidelines and protocol for enforcement.

Blood alcohol content is readily measurable by both breath and blood tests and can be used as evidence of a person’s level of “intoxication” at the time of driving in a DUI case.  In other words, a certain blood alcohol concentration will weigh heavily in the assessment of impairment due to intoxication.  In fact, California law sets a “per se” legal limit on what amount of alcohol can be in a persons’ blood before they are violating the law.  That level is a blood alcohol concentration of 0.08%.

Unlike alcohol-DUI blood concentrations, there is no per se legal limit as of yet for THC (one of the chemical compounds found in marijuana that’s what primarily gets a person “high”)  To further complicate things for law enforcement and the courts is the fact that unlike blood alcohol concentrations which rise and fall rapidly and are good indicators of how “drunk” a person may be, levels of THC in a person’s blood or urine are not necessarily good indicators of how stoned a person is/was.  THC can be detected in blood for several days after a habitual user stops smoking.  And THC in urine can persist for a month or longer.  A person may smoke in the morning and be fine to drive hours later, yet will have a high concentration of marijuana in their system.  So unlike alcohol, the average dissipation rate of marijuana in one’s system and the amount of the chemical in one’s system is not great evidence of intoxication.  A habitual smoker who quits for a week and takes a urine test might have the same concentration of THC as a person who has never smoked before but who smoked a joint minutes before being tested.

Fortunately, or unfortunately, some officers are being trained as “drug recognition experts” to detect marijuana intoxication.  These so-called experts go through a brief training course and learn things such as pupil dilation, heart rate, and other signs and symptoms of drug use.  However, these officers cannot rule out the many, many other factors that cause the exact same “signs and symptoms” of intoxication.  For example, elevated heart rate may occur when a person is under stress or nervous.  Does getting pulled over by a cop and being suspected of committing a crime ever get a person stressed or nervous?  Bloodshot eyes are a sign of marijuana use as well.  Ever heard of a red-eye flight?  It’s caused by being awake for an extended period of time or from eye strain.  Speech slurred, slow speech, lethargy, etc. – have you ever been tired?  Unfortunately, these “experts” will assess suspects and base their opinions on factors that can be explained away by normal every day life.  Some of the common myths surrounding marijuana use are still perpetuated by law enforcement.  For example, the myth that marijuana use turns a person’s tongue green still persists.

The person who is a habitual smoker or user of marijuana is in a tough situation if pulled over and investigated for a marijuana DUI who is sober.  An officer may immediately suspect the person of a marijuana DUI if the person has marijuana in the car.  The sober person’s blood-THC concentration may be high despite not being under the influence at the moment the person was driving.  Remember, it’s legal to be high on weed now, you just can’t be high at the time of driving.  Lastly, having THC in your system does not mean you are under the influence, since it can persist in a person’s system well after the effects wear off.  Having any % of alcohol in your blood on the other hand, can be evidence of driving under the influence of alcohol.

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