The Pennsylvania Superior Court has recently held that in (most) cases of suspected DUI-marijuana, prosecutors must introduce expert testimony that a person was, indeed, under the influence of marijuana at the time he was driving. That is, a police officer’s conclusions — without more — may not be enough.

The recent case involved involved a driver who was suspected of driving under the influence of marijuana. The police officer testified that she pulled over the defendant because of a non-working taillight. After she started speaking with the driver, she started to suspect that he may be under the influence of marijuana.

The police officer testified at trial that she performed sobriety tests on the defendant and that, in her opinion, his “eyelid and body tremors” were indicative of marijuana use. Based on this conclusion, she arrested him for DUI — marijuana.

At the conclusion of the trial, a jury found the defendant guilty.

The defendant appealed the conviction, raising arguments including the question of whether the officer’s opinion testimony that body tremors and eyelid tremors are indicative of marijuana impairment was improper.

The Superior Court agreed with the defendant and overturned the conviction, holding that the prosecution needed an expert witness (and not simply a police officer) to offer such an opinion at trial.

The Superior Court has held that in driving under the influence of marijuana cases, there is usually “a need for expert testimony”. In fact, the prosecution must produce an expert witness in such cases unless the circumstances are so obvious that there is a “clear connection between marijuana use and impairment.”

The Superior Court has provided an example of when an expert witness would NOT be required. In the case Commonwealth v. DiPanfilo, 993 A.2d 1262 (Pa. Super. 2010), the court noted that “if a police officer stopped a driver who was driving erratically, and the driver then rolled down his window and greeted the officer through a cloud of marijuana smoke, showing the typical signs of heavy marijuana use, it would be difficult to imagine that expert testimony would be necessary to establish the link between erratic driving and the driver’s marijuana use.”

However unless marijuana use is obvious to a lay person — such as the presence of a “cloud of marijuana smoke” — prosecutors can not simply produce the testimony of a police officer to conclude that a person is under the influence of marijuana.

Rather, prosecutors will need an expert witness.