The Cape and Islands district attorney has dropped a manslaughter charge in a fatal opioid-related overdose, citing a recent state Supreme Judicial Court decision.

The October ruling by the SJC in the case of Commonwealth v. Carillo has set a new stringent standard of proof for manslaughter convictions in narcotics cases.

In October 2018, Jason R. Willoughby, 34, of Vineyard Haven was indicted by a Dukes County grand jury on counts of manslaughter, distribution of a class B drug (fentanyl) and conspiracy to violate a drug law after a Vineyard Haven woman was found dead in her home of an apparent overdose. The death occurred in February 2018. The case has attracted widespread attention on the Island.

Prosecutors allege that Mr. Willoughby sold a half gram of the potent drug fentanyl to the victim’s boyfriend that led to her fatal overdose.

But on Thursday they abandoned the manslaughter charge, saying they had re-evaluated the case in light of Commonwealth v. Carillo.

“The commonwealth states that after review of Commonwealth v. Carillo and the totality of the particular circumstances, the facts do not support that the defendant knew, or should have known, that his reckless conduct created a high degree of likelihood of sustantial harm such as an overdose or death,” the district attorney said.

The filing was signed by assistant district attorney Jessica Croker, who is prosecuting the case.

The two other drug-related charges remain, with a trial set for next month in Barnstable Superior Court.

The felony manslaughter charge in the Willoughby case reflected a paradigm shift in the state’s strategy for combating the opioid crisis. As deaths from opioids, particularly fentanyl, have spiked in recent years, Massachusetts and other states began to use the manslaughter charge as a tool in the law enforcement arsenal.

But the decision from the state SJC in the Carillo case outlines a stringent standard of proof for manslaughter convictions in drug-related overdoses. In that case, a drug dealer was convicted of involuntary manslaughter after selling heroin to a UMass-Amherst student that led to an overdose and death. The case was appealed and made its way to the state’s highest court.

In the ruling, the Hon. Ralph Gants, chief justice of the SJC, said simply selling an overdose victim heroin did not meet the standard of “wanton and reckless” conduct necessary to result in a manslaughter conviction.

“We conclude that the mere possibility that the transfer of heroin will result in an overdose does not suffice to meet the standard of wanton or reckless conduct under our law,” the court said. “The commonwealth must introduce evidence showing that, considering the totality of the particular circumstances, the defendant knew or should have known that his or her conduct created a high degree of likelihood of substantial harm, such as an overdose or death.”

As a result, the defendant in the case was found not guilty and the manslaughter conviction was vacated.

The ruling outlined three different means by which state prosecutors could prove the defendant had known the sale would meet the likelihood of substantial harm threshold. They include evidence that the defendant knew the victim was particularly susceptible to overdoses, evidence that the defendant knew about the overdose and failed to seek help, or evidence that the defendant knew the drug was particularly potent or laced with fentanyl.

In the Willoughby case, the district attorney said it was determined that the circumstances were not strong enough to prosecute the manslaughter charge.

Robb Moriarty, an Edgartown attorney who is defending Mr. Willoughby, concurred.

“It’s the appropriate action to take in light of . . . Commonwealth v. Carrillo,” Mr. Moriarty said of the decision to drop the manslaughter charge. “As for the remaining counts, we intend to hold the commonwealth to its burden.”

A motion hearing is set for Jan. 17 in Barnstable, with a trial date scheduled for Feb. 10. The case was moved to Barnstable in November after the defense argued successfully that it would be difficult to find an impartial jury in Dukes County.