Denver, CO- Two states have legalized marijuana for recreational and in 20 states medical marijuana is legal. In all of these states there has been a push to develop standards of determining marijuana intoxication which is currently done using a blood test, but that could change in the future.
Researchers are working on a breath test, which could be used by law enforcement officers in the field, to determine whether a driver is under the influence of marijuana. In the study, which appears in the peer-reviewed journal Clinical Chemistry, researchers were able to detect THC—the active molecule in marijuana which causes the “high”– on the breath of participants shortly after they smoked marijuana.
According to the study, researchers collected breath samples from chronic marijuana users (people who smoked four times or more a week), after they smoked a joint with a 6.8 percent THC concentration.
They found that THC, which is thought to affect a person’s ability to drive, was detectable in the majority of breath samples. Researchers did not detect any THC-COOH, a marijuana metabolite that is found in the body after marijuana is consumed in any of the breath samples. Only one breath sample contained cannabinol, which has mildly intoxicating effects but is far less potent than THC.
Of the chronic users, all breath samples tested positive for THC just an hour after smoking. Subsequent breath tests showed the concentration of THC dropped over a period of time. Only one chronic user showed THC levels four hours after smoking.
For occasional pot users, 90 percent of users tested positive for THC one hour after smoking and again tested positive one and a half hours after smoking. One of the occasional smokers had no THC on their breath.
“Breath may offer an alternative matrix for testing for recent driving under the influence of cannabis, but is limited to a short detection window,” the researchers conclude in their paper.
Researchers said the detection window was between 30 minutes and two hours after smoking.
The intoxicating effects of THC are believed to last two to four hours after smoking. Peak THC levels can be detected within five to ten minutes of smoking.
Blood tests are the typically used to detect whether a person has THC in their system and states have developed a standard of 5 Nanograms of THC per milliliter of blood to charge a person with driving under the influence, which carries penalties similar to drinking and driving.
This is a controversial standard and lobbying groups believe that the 5 Nanogram standard is too high and that many people could be wrongfully charged with intoxicated driving. Habitual marijuana users can have 5 Nana grams in their bloodstream hours or days after the intoxicating effects of THC have worn off.
In one study, 25 participants tested positive for THC seven days after they abstained from smoking, so more research needs to be done to develop a more realistic standard for marijuana intoxication.
Once marijuana breath tests have been thoroughly tested and are developed for use in the field, people can avoid unnecessary marijuana DUIs.