(Denver Post) A proposal at the state Capitol to set a limit for how stoned is too stoned to drive died this evening in the Senate.
In a crucial vote, lawmakers rejected a hard cap on the amount of THC — the psychoactive chemical in marijuana — drivers could have in their systems above which they would be presumed too high to drive. Instead, a divided Senate sided with medical-marijuana advocates, who urged more study of the proposal.
Echoing the concerns of a number of lawmakers, Aurora Democratic Sen. Morgan Carroll said she believes the research is inconclusive about how much THC definitively causes impairment, meaning a 5-nanogram limit might snare sober drivers while allowing stoned ones to go free.
“If you’re going to have a shortcut to presuming somebody is impaired, let’s make sure the science is established,” Carroll said.
This is wonderful news, because the science is really inconclusive about regular cannabis use and driving impairment. My colleague Paul Armentano just alerted me to a new study that differentiates between infrequent users and regular users:
It concludes: “A threshold of 2-3ng/ml THC as an indicator of recent drug use (i.e, smoking within the previous 6 hours) as recommended by Huestis et al appears to be valid only for occasional users. Heavy cusers might exhibit measurable cannabinoid concentrations in blood, even if the last cannabis use was more than 24 hours ago. … Therefore, cannabinoid concentrations in heavy users’ blood from a later elimination phase might not be distinguished from an acute use of an occasional user.”
This reaffirms, in greater detail than the 2009 paper by Karshner et al, the residual phenomenon and how this could confound proper interpretation in DUI per se states.
Or as we saw in the case of the WestWord’s pot critic, William Breathes, who tested at 13ng/ml after sixteen hours of non-use of cannabis. Regular users do develop a tolerance and do not eliminate THC at the same rates. Let’s judge driving impairment by demonstration and not by body chemistry.