The Supreme Court’s review of a common lethal injection protocol is likely to be heard in April. (Jim Watson/AFP/Getty Images)

The Supreme Court announced Friday that it will review the drug protocol increasingly used in executions across the country to determine whether the procedure violates the constitutional ban on cruel and unusual punishment.

It is the court’s first examination of lethal injection since 2008 and follows a decision last week by a majority of the court — over the objection of its four liberal members — to allow the execution of Charles Frederick Warner in Oklahoma.

But it takes only four of the court’s nine members to accept a case, and that is apparently what happened during the justices’ private conference Friday. They will now consider a petition from three other inmates on Oklahoma’s death row this spring and render a decision in June.

One of the inmates is scheduled to be executed next week, and attorneys said they soon will file stay requests for all three.

Oklahoma Attorney General Scott Pruitt said his office will defend the state’s lethal injection procedures when the Supreme Court hears the issue this spring. In a statement, Pruitt promised “to defend the constitutionality of this protocol” so the state’s Department of Corrections can continue carrying out death sentences.

Charles Warner, shown in this 2011 file photo, was executed Jan. 15 for the 1997 killing of an 11-month-old girl. The Supreme Court declined to stay his execution. (Oklahoma Department of Corrections/AP)

Even as the number of executions across the country falls, the death penalty takes up an outsize portion of the Supreme Court’s time. Capital punishment raises complicated and highly divisive questions about how to humanely execute the perpetrators of some of the country’s most gruesome crimes.

If the challengers prevail in the latest case, states that want to use lethal injection would have to find a different protocol.

The court last rejected a challenge to lethal injections in 2008. “Simply because an execution method may result in pain, either by accident or as an inescapable consequence of death, does not establish the sort of ‘objectively intolerable risk of harm’ that qualifies as cruel and unusual,” wrote Chief Justice John G. Roberts Jr.

But the three-drug protocol used in the Kentucky case the court examined seven years ago — and employed in most of the executions at that time — is no longer available.

The use of this protocol raised objections from officials in Europe, where the majority of the drugs were manufactured, and from the companies producing them, leading to a shortage. States across the country have turned to new, largely untested combinations to execute inmates.

Those have resulted in several grisly moments that have brought new attention to the process. Most noteworthy was the April 2014 execution of Clayton Lockett, a convicted murderer who ultimately died 43 minutes after the procedure began.

As accounts of his writhing and grimacing spread, disapproval poured in from death penalty opponents as well as President Obama and the United Nations. Oklahoma Gov. Mary Fallin (R) ordered a review, and Robert Patton, head of the state’s Department of Corrections, asked that executions be postponed until the state could revise its execution protocol.

The new procedure, which went into effect in September, maintains the previous approach for lethal injection: a sedative to render the inmate unconscious, a second drug to paralyze him and a third to stop his heart.

But the protocol includes a much higher dose of the sedative midazolam. When Lockett was executed, 100 milligrams of the sedative were supposed to be injected; the state now says it will use 500 milligrams.

In her dissent last week in Warner’s case, Justice Sonia Sotomayor said she was concerned about Oklahoma’s use of midazolam as the first drug in the process. Although lower courts found the drug would work as intended, she said that was “difficult to accept given recent experience.”

Sotomayor noted testimony indicating that the application of the paralytic drug might render midazolam ineffective but that it would be impossible to know whether the inmate was conscious.

Joined by Justices Ruth Bader Ginsburg, Stephen G. Breyer and Elena Kagan, Sotomayor added: “Petitioners have committed horrific crimes, and should be punished. But the Eighth Amendment guarantees that no one should be subjected to an execution that causes searing, unnecessary pain before death.”

Dale Baich, one of the attorneys representing the Oklahoma death row prisoners, said the “lethal injection landscape” has changed significantly since the court’s 2008 Baze v. Rees decision.

“The drug protocol used in Oklahoma is not capable of producing a humane execution, even if it is administered properly,” he said.

A district court and panel of the U.S. Court of Appeals for the 10th Circuit found otherwise. Last week’s execution of Warner, who was put to death for raping and killing an 11-month-old girl, was carried out without much incident, witnesses said, although as the process began, Warner said, “My body is on fire.”

Before his execution, Warner was one of the parties petitioning the court to review lethal injection.

Also last week, Florida, which has used midazolam in executions since 2013, executed Johnny Kormondy, who was convicted of killing a banker and raping his wife in 1993.

Midazolam was involved in three problematic executions last year, raising concerns among civil liberties groups and attorneys for death row inmates.

In Ohio, where witnesses said the inmate choked and gasped, officials announced this month that they would no longer use a combination of the drugs midazolam and hydromorphone. The state also said it would have to delay an execution scheduled for next month, and possibly others, while it tries to obtain the drugs it hopes to use in the future.

Deborah W. Denno, a Fordham University professor who studies the death penalty and has been critical of lethal injection, said in a telephone interview that the court’s intervention was wise, since there are so many forms of the technique being used.

“Even though they’re all lethal injections, they’re all different kinds of executions,” Denno said. “We’ve never had anything like this in the history of this country, in the history of the death penalty.”

The problems facing places with lethal injection have occurred as the death penalty has become used less often. Last year, 35 inmates were executed in the United States, the smallest number in two decades.

The new case, Glossip v. Gross, will likely be heard in April.