"We ... agree that petitioners have not carried their burden of showing that the risk of pain from maladministration of a concededly humane lethal injection protocol, and the failure to adopt untried and untested alternatives, constitute cruel and unusual punishment," Chief Justice John Roberts said in an opinion that garnered only three votes. Four other justices, however, agreed with the outcome.
Roberts' opinion did leave open subsequent challenges to lethal injection practices if a state refused to adopt an alternative method that significantly reduced the risk of severe pain.
Justices Ruth Bader Ginsburg and David Souter dissented.
Executions have been on hold since September, when the court agreed to hear the Kentucky case. There was no immediate indication when they would resume, but prosecutors in several states said they would seek new execution dates if the court ruled favorably in the Kentucky case.
Forty-two people were executed last year among more than 3,300 people on death row across the country. Another roughly two dozen executions did not go forward because of the Supreme Court's review, death penalty opponents said.
The argument against the three-drug protocol is that if the initial anesthetic does not take hold, the other two drugs can cause excruciating pain. One of those drugs, a paralytic, would render the prisoner unable to express his discomfort.
The case before the court came from Kentucky, where two death row inmates did not ask to be spared execution or death by injection. Instead, they wanted the court to order a switch to a single drug, a barbiturate, that causes no pain and can be given in a large enough dose to cause death.
At the very least, they said, the state should be required to impose tighter controls on the three-drug process to ensure that the anesthetic is given properly.
Roberts said the one-drug method, frequently used in animal euthanasia, "has problems of its own, and has never been tried by a single state."
Kentucky has had only one execution by lethal injection and it did not present any obvious problems, both sides in the case agreed.
But executions elsewhere, in Florida and Ohio, took much longer than usual, with strong indications that the prisoners suffered severe pain in the process. Workers had trouble inserting the IV lines that are used to deliver the drugs.
Roberts said "a condemned prisoner cannot successfully challenge a state's method of execution merely by showing a slightly or marginally safer alternative."
Ginsburg, in her dissent, said her colleagues should have asked Kentucky courts to consider whether the state includes adequate safeguards to ensure a prisoner is unconscious and thus unlikely to suffer severe pain.
Justice John Paul Stevens, while agreeing with the outcome, said the court's decision would not end the debate over lethal injection. "I am now convinced that this case will generate debate not only about the constitutionality of the three-drug protocol, and specifically about the justification for the use of the paralytic agent, pancuronium bromide, but also about the justification for the death penalty itself," Stevens said.
Stevens suggested that states could spare themselves legal costs and delays in executions by eliminating the use of the paralytic.
Ty Alper, a death penalty opponent and associate director of the Death Penalty Clinic at the University of California-Berkeley School of Law, said he expects challenges to lethal injections will continue in several states.
