Despite the legal use of cannabis in many states, law enforcement officers still do not have the equivalent of a breathalyzer or blood test for cannabis.

Although a blood test exists which can detect some cannabis components, there is no standardized amount in breath or blood which give police a fair measure of impairment. A number of scientists are nationally working to create a chemical test and standard which will replace behavioral indicators officers base their judgement on now.

For Tara Lovestead, a chemical engineer at the National Institute of Standards and Technology, the biggest roadblock for research is the federal legality of cannabis. The cannabis plant is still illegal on the federal level, which makes acquiring a government sample much harder.

It is also difficult to chemically determine from blood or breath tests in which someone is high than to determine from a test which is under the influence of alcohol. Ethanol dissolves in water and easily digests in five hours, but the psychoactive ingredient in cannabis, tetrahydrocannabinol (THC), stores itself in body fat, which could stay in your system from 10 to 21 days.  

A number of companies are in the process of developing breath detection devices. Tara Lovestead is providing the data which will relate the concentration of THC detected in the breath to what is inside of the blood. In the future, Lovestead said looking at an accurate cannabis test will be similar to viewing many more chemicals than just THC.  

“Such a test would greatly reduce the possibility that someone might test positive from inhaling secondhand smoke,” she said.