The use of roadside sobriety tests (Field Sobriety Tests or FSTs) for the detection of marijuana influence in drivers is not supported by current research and studies. The Massachusetts Supreme Court recognized this in a recent decision concerning an officer’s testimony on an alleged marijuana-influenced driver’s FST performance. The court held that FSTs have limited value in determining whether a driver is under the influence of marijuana. Following this decision, while an officer in Massachusetts may testify as to his or her observations of a driver’s performance on FSTs, the officer cannot testify as to his or her opinion that the driver’s performance on the FSTs indicated impairment due to marijuana intoxication. The court’s decision was limited to officers who are not qualified as experts leaving the holding somewhat vague as to the testimony of an officer trained as a drug recognition expert (DRE). Like California, Massachusetts legalized recreational use of marijuana last year but driving under the influence of marijuana remains illegal.

The decision is particularly interesting in its review of the numerous studies on the efficacy of FSTs as a tool to detect marijuana impairment. Acknowledging the disparate conclusions among studies regarding marijuana’s effect on driver performance, the court observed that a significant number of the studies have reached the conclusion that marijuana consumption can impair a driver’s performance. However, the court’s review of studies that seek to determine whether a driver’s performance on FSTs is a reliable indicator of marijuana impairment yielded mixed results and different studies have produced contradicting results. As the court noted, studies suggest that the typical FSTs are inadequate indicators of marijuana impairment.

While there is no scientific agreement of the efficacy of FSTs to detect marijuana impairment, the court noted that an officer’s observations still have value when considered with other evidence. However, the court found that FSTs—as far as driving under the influence of marijuana is concerned—currently have no scientific foundation and should therefore not be treated as scientific evidence that a driver was under the influence of marijuana.

The Massachusetts decision has no effect on California law or admissible testimony in our courts but it may have broad implications as law enforcement struggles to address driving under the influence of marijuana. As I have previously discussed, with the rapid advent of legal marijuana across the country, law enforcement is rushing to catch up. The Massachusetts court implied that expert testimony is admissible but did not address the subject of officers trained as DREs. As I discussed last week, in Georgia, the use of DREs is being challenged on civil rights grounds. Meanwhile, scientists are scrambling to find reliable roadside tests that will detect marijuana impairment in a driver, but most states, including California, have not even determined what amount of THC is a per se amount above which the driver is impaired.

As the Massachusetts court noted, the effects of marijuana can vary greatly among individuals and there is no known study that has found any particular characteristics routinely present among individuals under the influence of marijuana or that indicated driver impairment due to marijuana usage. Without the science, such as we have with alcohol-impaired driving, arrests and convictions for driving under the influence of marijuana remain a substantially subjective endeavor. The upshot for the driver arrested for driving under the influence of marijuana is that there are more opportunities to defend the charge than there are with a hard-to-challenge BAC test results for the driver arrested for an alcohol DUI.

You may contact Orange County DUI attorney William Weinberg for a free consultation about your DUI matter at (949) 474-8008 or by emailing him at