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Scientists question the value of THC breath tests

On Behalf of | Sep 17, 2019 | Drunk Driving (DUI)

Breath-testing equipment used by police departments in Virginia and around the country often provide the key pieces of evidence in drunk driving cases. Prosecutors rely on toxicology test results when motorists are suspected of driving while influenced by alcohol because the link between elevated blood alcohol concentrations and intoxication is well established, but the science of THC impairment is more nebulous. Several companies are working to develop breath-testing devices that police officers could use to find out if motorists have smoked or otherwise consumed marijuana, but this equipment may be of little practical use even if it works.

The problem facing law enforcement is that THC and alcohol affect the body in different ways. A heavy drinker and a person who does not consume alcohol very often would both be unable to drive a car safely with a blood alcohol concentration of .08% or higher, but a habitual marijuana smoker could be relatively unimpaired by THC levels in their bloodstream that would leave somebody who rarely consumes the drug barely able to stand.

Blood test results are of little use in marijuana impairment cases because THC remains in the body’s system for up to a month. Breath-testing devices that use nanotubes to detect THC would reveal recent marijuana use, but this alone would not be enough to provide reliable evidence of impairment, according to scientists.

Criminal defense attorneys with experience in drunk driving cases will likely be paying close attention to the research being conducted in this area. Legal counsel could seek to have DUI charges dismissed when prosecutors are unable to provide compelling scientific evidence of impairment. An attorney could also question the reliability of alcohol testing when the equipment used was not properly maintained.