Determining the presence of THC in a person’s body is only the first step. That THC presence has to somehow be linked to impairment. How long does THC stay in the body? What level produces impairment. Are all people affected the same? Are there scientific evidence based answers? We don’t have the answers because it’s been illegal to possess it to perform those tests.
MassPrivateI: Marijuana breathalyzer in the works, why everyone should be scared.