Use of Sobriety Tests Hazy in Marijuana Cases

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By Patrick L. Gregory

Police can’t give an opinion at trial about whether a driver was impaired by marijuana based on field sobriety tests, the Massachusetts Supreme Judicial Court ruled Sept. 19 ( Commonwealth v. Gerhardt , 2017 BL 329063, Mass., No. SJC-11967, 9/19/17 ).

But field sobriety tests, or FSTs, are admissible “to establish a driver’s balance, coordination, mental acuity” and other skills needed for driving, the court said. Jurors may then rely on their “common sense about the effects of marijuana” as they weigh the evidence.

Research on whether FSTs can accurately determine marijuana impairment “has produced highly disparate results,” the court said. “The scientific community has not reached a consensus as to whether a defendant’s performance on any combination of FSTs, or any individual FST, is correlated with marijuana use or impairment,” it said.

“Because the effects of marijuana may vary greatly from one individual to another, and those effects are as yet not commonly known, neither a police officer nor a lay witness who has not been qualified as an expert may offer an opinion as to whether a driver was under the influence of marijuana,” it said.

The court noted that “marijuana is no longer a crime in Massachusetts for adults who are at least twenty-one years old,” but that driving under the influence of the drug is still a criminal offense.

The case shows how laws relating to marijuana use are evolving in the wake of successful legalization efforts.

To contact the reporter on this story: Patrick L. Gregory in Washington at

To contact the editor responsible for this story: Jessie Kokrda Kamens at

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