The US Supreme Court on Monday upheld the use of a controversial sedative in executions by lethal injection, saying it does not violate the Constitution.

In a 5-4 ruling, the court's five conservative-leaning justices said that the plaintiffs, death row inmates in Oklahoma, had not shown that use of midazolam constituted a "substantial risk of severe pain," and hence the drug does not violate the Constitution's eighth amendment ban on cruel and unusual punishment.