Gov. Jay Nixon on Friday stopped plans for the Oct. 23 execution of a death row inmate, citing controversy around the state’s planned use of propofol for the lethal injection and ordered prison officials to find a different drug. Missouri’s intentions for propofol, a popular anesthetic used at hospitals nationwide, have been criticized nearly from the start.

Here are five things to know about propofol and its role in the Missouri controversy:

Known as “milk of amnesia” for its white appearance, propofol is a general anesthetic that produces a quick and deep sleep for patients just before surgery. It’s among the most widely used anesthetics in U.S. hospitals and clinics. In recent years, it also has earned notoriety outside of medicine; propofol was found in pop star Michael Jackson’s system after his overdose death in 2009.

A DRUG FOR SANCTIONED DEATH

Amid questions in multiple death-penalty states about the constitutionality of various lethal drug combinations, Missouri changed its protocol from a three-drug blend to the single drug of propofol. Administered in high levels, the drug produces unconsciousness and stops a person’s breathing. But it has never been used in Missouri or any other U.S. state for an execution.

EUROPE’S WORRY

Roughly 90 percent of the U.S. supply of propofol comes from a single source: Germany-based Fresenius Kabi. But the anti-death penalty European Union recently threatened to add the drug to its export control list, which would jeopardize U.S. supply. The threat prompted the drug maker to implore Missouri to move away from propofol. But until Friday, Missouri’s governor seemed to be holding fast, saying earlier this week that courts generally had long upheld capital punishment and suggested this wasn’t the first time foreign countries had objected to products made, or actions taken, in his home state.

NIXON RELENTS, BUT …

Nixon’s apparent reversal Friday _ “As governor, my interest is in making sure justice is served and public health is protected” _ was cheered by death penalty opponents and eased worries that a vital component of surgical workflows in the U.S. would go untouched. But Nixon, a former Missouri attorney general who has long supported the death penalty, is not ending plans for Missouri to carry out executions. He’s ordering Department of Corrections officials to explore lethal injection alternatives.

WHAT’S NEXT:

While the state explores the options, the planned Oct. 23 execution of Alan Nicklasson is off and Nixon said the state would “immediately request” a new execution date. It’s unclear what that means for the planned Nov. 20 execution for another convicted killer, Joseph Franklin.