Voters in California chose to make the recreational use of marijuana legal in November 2016, and law enforcement agencies in the state expect to encounter more motorists under the influence of the drug as a result. This is a problem because police officers do not have a reliable way of telling whether or not a motorist is impaired by THC. Alcohol testing is effective because levels of alcohol detected in breath and blood samples can be reliably linked with degrees of intoxication in both large and small individuals regardless of how much they drink. However, THC testing is far more scientifically nebulous.
Individuals who consume large amounts of marijuana on a regular basis may show few signs of impairment with blood THC levels that would leave casual users of the drug incapacitated, and traces of the metabolite can be detected in blood samples days or weeks after its intoxicating effects have abated. Scientists have been looking for an accurate and reliable way to test breath samples for THC, but the complex chemical structures of psychoactive compounds have stymied this work.
However, the National Institute of Standards and Technology has reported that a breakthrough has been made in this area. NIST Scientists concentrated on vapor pressures to monitor liquids as they convert to gases in the lungs, and their findings suggest that they were able to measure the vapor pressure of THC for the first time.
Experienced criminal defense attorneys may demand strong scientific evidence and call for rigorous testing before new toxicology testing equipment is issued to police departments. The results of these tests provide crucial evidence against people facing drunk driving charges, and attorneys could argue that admitting evidence with questionable scientific merits is prejudicial to their clients.