The US Supreme Court has upheld Oklahoma's use of a drug in its lethal injection process for death-row inmates.

In a 5-4 vote on Monday, the Supreme Court said the use of midazolam as the first drug in Oklahoma's three-drug protocol in lethal injection did not violate the Eighth Amendment's prohibition against cruel and unusual punishments.

The lawsuit stemmed from the filing of a motion for preliminary injunction by three death-row inmates with a district court seeking to stop Oklahoma from carrying out its death penalty procedure. The district court denied the motion, which was upheld by an appeals court.

Justice Samuel Alito wrote the majority decision, stating that the inmates failed to show there was an alternative method of execution available that would be less painful, according to Reuters.

"And because some risk of pain is inherent in any method of execution, we have held that the Constitution does not require the avoidance of all risk of pain," according to the majority decision. "After all, while most humans wish to die a painless death, many do not have that good fortune. Holding that the Eighth Amendment demands the elimination of essentially all risk of pain would effectively outlaw the death penalty altogether."

Justice Stephen Breyer, in his dissenting opinion, said today's use of the death penalty involves "three fundamental constitutional defects": serious unreliability, arbitrariness in application, and unconscionably long delays that undermine the death penalty's penological purpose in addition to the fact that most places in the US have abandoned its use.

He noted that a prisoner who is sentenced to death is two or three times more likely to have his sentence overturned or commuted.

"In a word, executions are 'rare.' And an individual contemplating a crime but evaluating the potential punishment would know that, in any event, he faces a potential sentence of life without parole," he said.

He declared "I believe it highly likely that the death penalty violates the Eighth Amendment."

Justice Antonin Scalia said Breyer's opinions were full of "internal contradictions" and were "gobbledegook."

The Supreme Court reinstated the death penalty in the US in a 1976 decision, finding that its use did not constitute cruel and unusual punishment. In the US, there are 31 states that have the death penalty, according to Reuters.