LAWRENCE — Joshua Miller’s long struggle with opiate addiction ended on July 13, 2015, on the bathroom floor of a sober house in Lynn.

That’s where his brother, Keith McEvoy, found the 37-year-old carpenter unconscious, his face blue and puffy. Crouched in a shower stall, McEvoy watched frantically as paramedics tried to revive his older brother, who had overdosed on fentanyl he had bought from his dealer, Carlos Hunter.

“The worst day of my life,’’ McEvoy said in a statement his mother read aloud in Lawrence Superior Court on Thursday, a week after Hunter, 33, was convicted of involuntary manslaughter in Miller’s death.

Miller’s mother watched in a Lawrence courtroom as Hunter was sentenced to eight to 12 years for his crime, a punishment legal specialists said was unusually tough but could become more common as lawmakers push for tougher penalties of opioid dealers.

In August, Governor Charlie Baker filed legislation that would create a new manslaughter charge for drug dealers whose product causes a death. Dealers would face a mandatory sentence of five years.

“I think we’ll see more indictments of drug pushers for involuntary manslaughter after they’ve caused the death of addicted individuals,’’ said Martin Healy, chief legal counsel for the Massachusetts Bar Association. “There is a new focus by policy makers to hold dealers responsible for the human carnage that they leave in their wake.’’

But critics questioned the get-tough approach. Leo Beletsky, associate professor of law and health sciences at Northeastern University, said studies suggest that prosecutions of dealers are unlikely to curtail the supply of heroin and fentanyl, and wind up siphoning public funds away from treatment options.

“What is accomplished other than vengeance, other than saying, ‘We have this awful problem on our hands and someone had to pay’? ’’ Beletsky said. “There is no question in my mind that this is a huge waste of resources.’’

Essex Assistant District Attorney Kelleen Forlizzi said investigators spent hundreds of hours combing through Hunter’s phone, where they found text messages in which he bragged about the potency of the drugs he sold.

Lawrence Superior Court Judge Mary Ames described Hunter as a “glib and successful’’ dealer who preyed on people addicted to heroin. His lawyer, John Apruzzese, sought a three- to five-year sentence, saying Hunter was not aware he had sold fentanyl, which resembles heroin, to Joshua Miller and had not intended to kill him.

Miller, a father of two young boys, had asked Hunter for heroin, Apruzzese said.

Hunter also struggled with drug addiction, Apruzzese said. But Ames said the evidence at trial undercut that defense.

“I reject the notion that the defendant was acting because of his own addiction,’’ Ames said. “This was the ultimate salesman . . . selling absolute poison on a daily basis as others might ply any other honorable trade.’’

Hunter is already serving a 2½-year sentence after pleading guilty to dealing fentanyl to an undercover officer in July 2015, two weeks after Miller’s death. Apruzzese asked Ames to give Hunter credit for the time he has served on that sentence, noting that the two cases were part of the same investigation. Judges often give concurrent sentences on separate charges when they are part of the same case. Ames refused Apruzzese’s request.

Involuntary manslaughter carries a maximum sentence of 20 years, and prosecutors had sought 12 to 15 years. Legal observers described the sentence as steep. Similar convictions have prompted sentences ranging from 18 months to six years, they noted.

In handing down the sentence, Ames cited Hunter’s long criminal record, which began in 1999 and included violating a restraining order, assault, and heroin distribution in 2007, a conviction the judge said she found particularly troubling.

“Really, the record doesn’t slow down after that,’’ Ames said. “It just gets worse.’’

After the hearing, Miller’s mother, Diana McEvoy, said she hoped the conviction and long sentence would give dealers pause.

“To me, no sentence is good enough. That was my child. That was my son,’’ she said. “I just pray . . . that hopefully one more family won’t lose a child, a father, a brother to this.’’

Maria Cramer can be reached at mcramer@globe.com. Follow her on Twitter @globemcramer.