What Should the Blood Limits for THC Be?

Now that cannabis is legal in eight states for recreational use, and numerous other states for medical use, the issue of how to handle driving under the influence of cannabis (DUIC) is currently being hotly and heavily debated.  Many states, both where cannabis is legal and where it is illegal, currently set an arbitrary non-zero number for their blood-THC limit, while others set the limit at zero (i.e. zero-tolerance), while still others do not set any specific per se limit despite driving while impaired being illegal.  And as of 2017, there remains zero evidence that any of these laws actually save any lives on the highways or otherwise.

Recently, the state of Oregon, where cannabis is legal, has effectively stopped enforcing their legal per se limit for THC, citing a lack of scientific evidence to justify such a policy.  To wit, the Oregon Liquor Control Commission’s report on the matter also supports the idea that cannabis is far less impairing than alcohol:

“The rate of drivers tested by Drug Recognition Experts who are positive for THC intoxication rose between 2013 and 2014, but did not increase following legalization [in 2015]. Fatal accidents data is highly variable year-to-year, making trend analysis difficult. But in Oregon in 2015 there were only three more traffic fatalities involving a driver testing positive for THC compared to 2004. Moreover, the rate of THC-related fatal accidents is also considerably lower than such accidents involving alcohol intoxication. Finally, while overall traffic fatalities and alcohol-related fatalities spiked in 2015, THC-related fatalities did not."

Even the AAA now concedes that, while being high on weed can cause driving impairment, it is significantly less impairing than alcohol and is in fact comparable to driving with a “noisy child in the back of the car,” and only half as dangerous as talking on a hands-free cellphone (which is legal in all states).  That said, we should also note that different drivers may be affected differently, and novice users and/or novice drivers may be a lot more impaired than more experienced users and/or drivers.  And combining cannabis with alcohol is known to be significantly more dangerous in terms of driving impairment than either one alone as well.  But there is currently no scientific evidence strong enough to justify a zero-tolerance or per se limit for THC, as its pharmacokinetics are far too complex to correlate blood THC levels with actual driving impairment.  For example, frequent users (including medical users) can test positive several days after the last time they used it, even if they are not impaired in the least, and thus get unjustly snared in the same dragnet as those who are actually impaired from toking up an hour or two ago.

Twenty-One Debunked does not recommend that anyone drive under the influence of cannabis.  But our laws must reflect reality nonetheless.  Thus, we make the following recommendations:

• Follow Colorado's lead and set a prima facie limit for THC instead of a per se limit.  That distinction is crucial, as that would not mean automatic guilt, but a rebuttable presumption of guilt for going over the limit, which can still be challenged in court to prove non-impairment.
• Set the limit at no lower than Colorado's 5 ng/mL, as that level, though imperfect, provides the clearest separation between impaired and non-impaired driving according to the best research.  Zero tolerance = zero intelligence.
• Do not test for inactive metabolites, except perhaps to confirm recency of use.
• Increase the use of field sobriety tests and drug-recognition experts, and use saliva tests to check for recent cannabis use before drawing any blood.
• Work on developing better methods of determining actual impairment, but do NOT use that as an excuse or delaying tactic for keeping cannabis illegal.
• Consider allowing a "medical necessity" defense for medical users.
• Make the penalties for DUIC alone significantly lower than for alcohol and other drugs, but in combination with other substances, or if anyone is injured or killed, throw the book at 'em!
• For illicit drugs other than cannabis, a per se limit would in fact be appropriate.
• Get much tougher on bad and reckless drivers in general, as well as distracted driving.
• And in keeping with the overall mission of Twenty-One Debunked, set the age limit for cannabis at 18 and do not treat drivers aged 18-20 any differently than drivers over 21 with respect to cannabis.

In other words, facts > feelings, even in the "post-truth" era.

We should also note that the rather modest increase in traffic deaths in 2015 and 2016 nationwide, and in 2014 in some states as well, does NOT seem to be caused by recent cannabis legalization in several states.  Increases occurred in both legalized and non-legalized states, as did some decreases, and there was no clear pattern in that regard.  A much more plausible explanation is the massive drop in gas prices from late 2014 to 2016, which is known to increase traffic fatalities (all else being equal), along with the improving economy as well as "reversion to the mean" following an all-time record low per VMT in 2013-2014.  Ergo, QED.