Ohio on Nov. 13 became the first state to adopt a procedure for lethal injections that uses one drug, a method never before tried on U.S. inmates.

The state filed papers in U.S. District Court saying it has decided to switch from a three-drug cocktail to a single injection of thiopental sodium into a vein. A separate two-drug muscle injection will be available as a backup.

The decision comes two months after an Ohio death row inmate walked away from an unsuccessful execution and subsequent executions were put on hold.

Several states have faced similar challenges, but Ohio is the first to drop the three-drug approach in favor of one dose.

Richard Dieter, director of the nonprofit Death Penalty Information Center, said the method has never been attempted on humans.

“Unfortunately, this is really going to be an experiment,” he said.

“They’re human subjects and they’re not willingly part of this. This is experimenting with the unknown and that always raises concerns.”

He said the method has been used in euthanizing animals.

The death penalty has been temporarily on hold in Ohio while the state developed its new policies. The update follows a botched execution on Sept. 15 that was halted when executioners couldn’t find a suitable vein on inmate Romell Broom.

Broom, who was convicted of kidnapping, raping and killing a 14-year old girl in 1984, complained in an affidavit following the execution attempt that his executioners painfully hit muscle and bone during as many as 18 attempts to reach a vein.

The state said in a court filing last month it was having a hard time finding medical personnel willing to consult about injection because of professional and ethical rules. The rules – which generally prohibit doctors, nurses and others from involvement in capital punishment – were deterring such personnel from speaking publicly or privately about alternatives to the state’s lethal injection process.

Ohio has put 32 people to death since 1999, when executions resumed in the state.