According to a ruling made on Tuesday by the Massachusetts Supreme Judicial Court, field sobriety tests used in drunk-driving cases cannot be used as evidence for drugged-driving cases involving cannabis.

The court said officers are only allowed to testify as non-expert witnesses and make observations on how an individual performed during a sobriety tests. They are also not allowed to tell juries the defendant’s results of tests or offer opinions on whether a driver was too high to drive. 

The justices said there is no reliable scientific test for cannabis impairment comparable to tests for blood alcohol content. In drunk-driving cases, results of field sobriety tests can be paired with blood alcohol readings as evidence of impairment.

“While not all researchers agree, a significant amount of research has shown that consumption of marijuana can impair the ability to drive,” the court said in a unanimous decision. “There is ongoing disagreement among scientists, however, as to whether [field sobriety tests] are indicative of marijuana impairment.”

The state legislature recently created a special commission to study driving under cannabis impairment.