The state of Florida is stockpiling a toxic substance which may or many not be used in state-sponsored executions, and no one is sure why.

Most states that still have capital punishment have been using the “lethal injection” method, but one of the drugs used in these executions – a sedative known as midazolam – has been in short supply recently.

In Florida, this has resulted in a delay in executions. To date, there are 400 death row prisoners sitting in Florida prisons, where there have been no executions in almost a year. According to the Tampa Bay Times, the Sunshine State has 250 vials of midazolam on hand, which would cover about a dozen executions, but those vials are close to their expiration date. In response to this situation, the State of Florida is stockpiling a different drug to replace it – a rapidly-acting anesthetic called etomidate.

The problem is that while etomidate is used successfully by the medical profession for conscious sedation, it has never been employed in the “drug cocktails” used for state-sanctioned executions. In light of several botched executions involving midazolam, this decision by the state is raising many questions.

Medically, midazolam is used as an emergency treatment for seizures, as a sedative for general anesthesia, and to treat certain psychological and sleep disorders. Its purpose in executions is to put the condemned prisoner under, after which vecuronium bromide and potassium chloride are injected to stop respiration and the heart.

A controversy arose in 2014 after an inmate named Clayton Lockett appeared to regain consciousness after being administered midazolam. A lawsuit was then filed by a trio of death row inmates in which lawyers for the plaintiffs argued that the use of midazolam was insufficient to fully render a prisoner unconscious, and therefore constituted cruel and unusual punishment. A similar lawsuit was filed in Arizona after a convicted murderer named Rudolf Wood took two hours to die during an execution.

Despite the legal controversies surrounding midazolam, Florida is now preparing to move forward with executions using etomidate – which has never before been employed for that purpose.  etomidate suppresses the production of corticosteroids, hormones made in the adrenal cortex and regulate stress and immune response, among other things. It is also used in the operating room in order to induce general anesthesia as well as in conscious sedation procedures.

Aside from the fact that etomidate has never been used in an execution, its introduction into the process is certain to raise more legal challenges – particularly because Florida intends to introduce other new, untested drugs into its execution “cocktails.”

Maria DeLiberato, who is representing a death row inmate in his lawsuit challenging the state’s lethal-injection protocol, says that Florida’s use of a new and untried combination of drugs “essentially amounts to human experimentation.”

So far, the Florida Department of Corrections has no comment.