Efforts to better identify and prosecute impaired drivers are laudable, but the enactment of unscientific and inadvisable ‘per se’ legislation for THC — the primary psychoactive compound in marijuana — and its inert metabolites (byproducts) is not a scientific or advisable approach to addressing traffic safety. Nonetheless, sixteen states now impose either ‘per se’ or zero tolerant ‘per se’ laws for motorists who operate a vehicle with even trace levels of these constituents in their blood or urine, regardless of whether or not they are behaviorally impaired. (Other states require evidence of recent drug use and evidence of behavioral impairment due to said use in order to go forward with a DUI drugs charge.) Additional states, like California, are proposing similar ‘per se’ laws for pot.
Such legal ‘per se’ limits for cannabinoids are arbitrary and problematic. Here is why.
Both THC and carboxy THC (THC-COOH), may be detectable for periods of time extending beyond any reasonable period of impairment, such as days (in the case of THC) or weeks (in the case of carboxy THC). As a result, the US National Highway Traffic Safety Administration affirms, “It is difficult to establish a relationship between a person’s THC blood or plasma concentration and performance impairing effects. … It is inadvisable to try and predict effects based on blood THC concentrations alone, and currently impossible to predict specific effects based on THC-COOH concentrations.”
The United States Department of Transportation Drug Expert Recognition Training materials similarly acknowledge: “Toxicology has some important limitations. One limitation is that, with the exception of alcohol, toxicology cannot produce ‘per se’ proof of drug impairment. That is, the chemist can’t analyze the blood or urine and come up with a number that ‘proves’ the person was or wasn’t impaired.”
– Read the entire article at AlterNet.