The state will join several others that have substituted pentobarbital — a sedative often used to euthanize animals — for sodium thiopental in their execution protocols.
Sodium thiopental is in short supply in the United States after an Illinois company bowed to European Union pressure and stopped making it.
Texas, Oklahoma and Ohio already have made similar changes.
Hood had asked the state Supreme Court to schedule executions for April 20, April 27 and May 4.
The first would be Robert Simon Jr., who was sentenced to die for the 1990 killings of a couple and their 12-year-old son.
The attorney general also has requested execution dates for Rodney Gray, convicted of killing a 79-year-old woman in 1994, and Benny Joe Stevens, sentenced to death for the 1999 slayings of four people.
Mississippi Corrections Commissioner Chris Epps said the state has ordered the new lethal injection drug and has been rehearsing for the expected executions.