Joseph P. Hougnon, Attorney at Law

Marijuana DUID’s and Per Se THC Limits Part 4

Reefer Madness – Science vs. Hysteria

Science vs. Per Se THC Laws in Marijuana-related DUID’s

Now that it’s legal to consume marijuana for personal use in California, the same concerns the scientific community has expressed regarding medical marijuana patients applies to those who consume marijuana for personal use. Those who consume marijuana regularly tend to develop a tolerance to the impairing effects of the drug.

As I wrote in previous chapters of this blog, most states, including California, do not have “per se” limits for Driving Under the Influence of Drugs (DUID) cases, as they do for alcohol-related DUI’s. If you have drugs in your system and you’re arrested for suspicion of DUID in California, the District Attorney will have the burden to prove beyond a reasonable doubt your ability to drive was impaired, as they do in alcohol-related DUI’s, where the driver’s BAC is below .08% or more [CVC section 23152(a)].

If California were to pass a per se law for marijuana-related DUI’s, however, the presumption of innocence would no longer apply to those whose THC levels are at or above the threshold set by the legislature, as those who are driving with a BAC at or above the legal limit of .08% are presumed guilty by law in alcohol-related cases. Indeed, some states have taken this approach to Marijuana-Related DUID’s, enacting “per se” laws for drivers with relatively low levels of THC.

Several states have passed per se THC limits for marijuana-related DUID’s. The question is whether California will decide to pass similar laws, and whether science will play a key role in their decisions?

Colorado & Washington have passed per se limits for marijuana-related DUID’s. Drivers with THC levels in their blood equal 5 nl/Ml or more are presumed guilty of DUID’s.

As studies have shown, the one-size-fits-all per se approach to marijuana-related DUID’s flies in the face of actual science and will lead to the arrest of some drivers who are not impaired at all, as well as those who may not have consumed marijuana several days, or even weeks.

Andrea Roth, an Assistant Professor of Law at the University of California-Berkeley, wrote an article that has gained a lot of attention, “The Uneasy Case for Marijuana as Chemical Impairment Under a Science, Based Jurisprudence of Dangerousness.” Ms. Roth argues these numerical per se limits for marijuana are scientifically unfounded.

“There is no demonstrated linear or predictable relationship between THC blood limits and an increased relative crash risk,” she said. “The smoking gun of causation is case-control studies and single-car fatal crashes.”

Roth analyzed four studies that provided data on THC and single-car fatal crashes and nine case-control studies that surveyed randomly stopped drivers about THC use. Roth concluded that none of the studies suggested a relationship between THC levels and an increased crash risk. She added, We shouldn’t be relying on completely, scientifically illegitimate per se laws to convict people.”

In February 2015, the NHTSA released a study that explored crash risk associated with drugs and alcohol. In the executive summary, the NHTSA touted the study as the “largest and most carefully controlled of its kind.”

The report ultimately concluded that when alcohol consumption and demographics were controlled, there was no “increase in population-based crash risk associated with THC use.”

According to Roth, “No one really disagrees with this as a matter of science. There is no linear, predictable relationship between blood THC levels and an increased relative crash risk.”

States like Delaware and Wisconsin, on the other hand, go even further and have zero-tolerance policies, which means any detectable amount of marijuana can result in a traffic safety conviction.

Critics argue that per se limits and zero-tolerance policies are invalid without scientific evidence to support them. As an alternative, they recommend that states use effect-based standards that already exist, meaning that law enforcement has to prove that a driver was impaired by marijuana based on the totality of evidence, including their driving behavior, not just levels of THC found in blood or urine samples.

“In every state already, it is a criminal violation to drive under the influence of a substance that can impair judgment,” NORML’s Armentano said. “There is no need to amend those laws in a manner that is entirely arbitrary and unscientific,” he said. “If we’re concerned about individuals driving impaired, then the last thing we ought to do is amend the traffic safety laws so that a guilty conviction is divorced from any evidence of impairment.”

Most scientists researching the issue acknowledge the difficulty of pegging THC impairment to a number (in a way similar to drunk driving laws), and epidemiological evidence on the risk of accidents associated with marijuana is much less conclusive than data regarding alcohol, according to The Marijuana Policy Project in Washington, D.C. (MPP, “Driving Under the Influence Laws and Medical Marijuana Patients: Zero Room for “Zero Tolerance”).

According to MPP, “pushes to enact a per se THC limit or a zero tolerance DUID law are a particular concern for medical marijuana patients who tend to use marijuana more frequently than the general population of marijuana users. These laws may make some patients have to give up legally driving — even when they are completely unimpaired — if they want to use the medicine that works best for them. In addition to being unfair to patients, research indicates per se DUID laws do not make the roads safer.”


A “per-se” approach to marijuana-related DUID’s is not supported by science. California is likely to take up this issue soon now that Proposition 64 has become law. The question now is whether California will follow the lead of states like Colorado and Washington and pass per se DUID laws for marijuana-related DUID’s?

Let’s hope politicians and law enforcement, as well as the public at large, become educated on this issue before legislature considers enacting per se limits for marijuana-related DUID’s.

Let’s push our legislators to consider the actual science and ask them to stand against fear, ignorance and hysteria, which has been at the forefront of the public discourse on this issue for so many years. This time around we should listen to the scientists. But, if our politicians choose to ignore science and facts, its almost certain it will result in potential injustices, as well as higher law enforcement and court costs, as many innocent people are likely to be arrested and convicted for marijuana-related DUID’s even though they are driving sober.


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About the Author

Since 1996, Joe Hougnon, Esq. has provided the best legal services for DUI, Criminal charges & personal injury cases in northern California.