Now that recreational use of marijuana is soon to be legal in Colorado and Washington, state law enforcement, legislators, and prosecutors have expressed concern about how best to handle marijuana DUI charges. Their concerns are twofold: what is the best way to test for active THC in individuals, and at what threshold of THC should be there be a statutory presumption of impairment.
A big issue with testing accuracy is the distinction between THC and THC metabolites. THC metabolites are inactive and can remain in body fat for around one month, while regular THC is active and dissipates in the blood over time similarly to alcohol. Currently, blood tests can accurately measure active THC for use in DUI investigations, though the issue of distinction remains. For heavy users THC metabolites can stay in the blood-stream for up to two weeks. On the surface this distinction may seem obvious, but in a court of law any amount of vagueness can cast doubt. Clarification lacking in the distinction of THC and THC metabolites in regards to drug testing and how those tests are administered creates an opening for argument. Though Georgia has not legalized recreational marijuana use, marijuana has a very specific definition under Georgia law to combat vagueness in prosecution.
The second issue stems from a statutory presumption of impairment corresponding to a specific blood-THC level. Many states, Georgia included, have a presumption written into their DUI laws that a blood-alcohol level of .08% constitutes impairment regardless of field sobriety tests, demeanor, or manner of driving. Washington adopted a standard of 5 nanograms of THC per milliliter of blood, though opponents are concerned that lack of information regarding marijuana testing and impairment makes any presumption arbitrary. Considering that blood-alcohol legal limits have dropped from .15 grams per 2.1 liters of air to .08 grams per 2.1 liters in the last forty years, generally without meaningful evidence supporting such a drop, concerns regarding setting initial impairment levels are legitimate. Though Georgia's history of conservatism doesn't put it on the short list for states working to legalize marijuana, if or when legalization occurs, the practices of states like Washington and Colorado will inform the implementation for the rest of the country.