With marijuana legalization in Colorado and Washington, and the possibility of other states following suit, DUI laws for pot are becoming a huge point of contention.
This map, from Denmon & Denmon Trial Lawyers, shows the three ways states can charge drivers with DUI. The white states on the map have no driving laws specific to marijuana at all.
To land a conviction in yellow states, prosecutors must directly relate the impairment to the ingestion of marijuana, regardless of actual levels in the blood. The green states' laws, however, list a legal limit for drug metabolites. In red states, any marijuana presence could put a driver in cuffs.
Some people think it's crazy to set limits for marijuana DUI. For states that do require specific levels for conviction, testing becomes necessary. Many of these methods vary in their accuracy though, according to NORML, a pro-marijuana legalization nonprofit.
Urinalysis
Contrary to popular belief, urinalysis can't detect the presence of any illicit drugs, including marijuana. It can only identify the presence of non-psychoactive drug metabolites (compounds from chemical changes in the body caused by drugs, not drugs themselves). Cannabis metabolites can be detected in the blood up to a month after use, so it's impossible to know exactly when the person took the drug, according to NORML. States mostly consider urinalysis unreliable for DUI testing.
Blood Test
Blood tests detect the actual drug, not the inactive metabolites. Generally, THC is only detectable in the blood for a few hours. Chronic smokers may show low, residual levels for up to 24 hours, though.
Because of this narrow detection window, blood tests are typically considered reliable for DUI conviction.
Hair Test
Considered unreliable, hair strands testing also detects the presence of metabolites that have moved from the blood stream to the hair follicle. This test, however, is more sensitive to minorities and people with darker hair as well as the elderly (with grey hair), according to NORML.
High humidity can also rapidly break down marijuana metabolite levels in the hair of heavier smokers, increasing the chances of a false-negative.
Breathalyzer
Breathalyzers for drug detection are a relatively recent invention. One of the first hit the scene in spring 2013. Created by a Swedish company, the device correctly identify drug use in 87% of cases, according to U.S. News & World Report. Critics say, however, that these devices can only detect drug use, not levels or state of impairment.
"To date, no such data exists correlating THC/breath detection levels with behavioral impairment," NORML's Paul Armentano wrote for High Times.