Police officers in California and around the country may soon be issued with portable devices that are able to detect the compound that gives marijuana its psychoactive properties in a breath sample, but legal experts and scientists are not convinced that the results of these tests will be of any real value. One of the THC breath-testing devices currently being tested uses nanotubes thousands of times smaller than a human hair to detect THC. Its developers say that it will only return a positive result when marijuana has been consumed recently, but even that may not be enough to support an impaired driving charge.
This is because scientists are not able to link specific THC levels with degrees of impairment. Any driver with a blood alcohol level higher than the .08% driving limit is considered legally intoxicated, but no such measurement exists for THC. Casual marijuana users could be dangerously impaired with levels of THC in their bloodstreams that a habitual smoker would barely even notice, which means that the results of a THC breath test alone would not be enough to establish impairment beyond reasonable doubt.
The federal government still considers marijuana a Schedule I drug, which has hampered research in this area. However, scientists hope that studies being conducted in Canada and states where marijuana has been legalized could soon lead to a breakthrough. Until then, identifying marijuana impairment will remain a challenging task for law enforcement.
Toxicology test results are generally the key pieces of evidence in impaired driving cases, and experienced criminal defense attorneys might seek to have DUI charges dismissed when they could be unreliable. Blood alcohol concentrations may be more conclusive than THC levels, but even these results could be challenged if the equipment used was not regularly recalibrated or strict testing procedures were not followed.