Supplies of the controversial sedative midazolam have dried up and further supplies of the drug were blocked by lobbying of European pharmaceutical suppliers by death penalty activists. The shortage of the drug was uncovered in a legal challenge to Arizona's method of killing death row convicts when Joseph Wood was injected with midazolam in 2014 and he was still alive after two hours. Eyewitnesses at his execution saw him struggling to breathe.

Woods was given 15 injections of midazolam and a painkiller. His lawyer condemned the execution as botched. According to Michael Kiefer, a reporter for the Arizona Republic and witness to Woods' execution, the death row prisoner made gasping sounds and took more than 640 breaths before he finally died.

A lawsuit was filed on behalf of seven death-row inmates who allege that Arizona's use of midazolam and two other drugs violate the US Constitution's ban on cruel and unusual punishment. Arizona has more than 100 inmates on death row at a state prison in Florence. Executions in Arizona are halted until the lawsuit is resolved.

Dale Baich, one of the attorneys representing death row prisoners said in an AP report: "It's our belief that the unlimited discretion that the director has during the execution process violates the Eighth Amendment," which forbids cruel and unusual punishment. In April 2014, Oklahoma, Clayton Lockett a death row inmate was left in terrible agony for nearly an hour, before dying of a heart attack, after an injection of midazolam failed to render him unconscious.

According to state lawyers at Phoenix's US District Court: "What is more, the department's source of midazolam has vanished under pressure from death penalty opponents." The Department of Corrections stated that they also lacked the execution drugs pentobarbital and sodium thiopental.

Drug company Pfizer said in May that it had banned the sale of execution drugs, including midazolam, which is a relative of Valium. The move has now blocked off the last major source for the US of drugs for a lethal dose combination.