NASHVILLE (AP) — The state Supreme Court is scheduled to hear oral arguments on Thursday morning over whether Tennessee's lethal injection protocol constitutes cruel and unusual punishment.

Thirty-three death row inmates sued after the state moved from a three-drug lethal injection method to a one-drug method using pentobarbital. Their attorneys argue that the compounded form of the drug is likely to cause a condemned inmate to suffer extreme pain and can cause a lingering death.

Tennessee's protocol calls for the use of pentobarbital mixed to order by a pharmacist. That's because the only commercial producer of the drug has placed restrictions on its distribution to prevent it from being used in executions.

Tennessee has not executed an inmate in nearly six years because of legal challenges and problems in obtaining lethal injection drugs.