The death chamber as seen from the viewing room at the state penitentiary in Huntsville, Texas. Thomson Reuters Arkansas' plan to execute seven men by lethal injection over the course of 10 days in April hit a road block Friday when a federal judge moved to block all of the executions by issuing a restraining order against the state's use of the drug vecuronium bromide.

Arkansas was pushing to carry out the executions before one of the drugs used as part of the fatal cocktail expired.

Perhaps unexpectedly, the leading opponents of the executions were the very companies that produced the drugs.

Four companies have spoken out so far about the executions in Arkansas: Pfizer, Fresenius, West-Ward Pharmaceuticals, and the drug wholesaler McKesson.

There are three drugs typically used in the lethal-injection cocktail:

Midazolam , which is used as an anesthetic. In medicine, it's used to make people drowsy before surgery and as a way to produce memory loss so patients don't remember painful parts of the procedure. Midazolam is the drug set to expire in Arkansas, and its use has been controversial because of its role in recent botched executions in which patients remained conscious.

, which is used as an anesthetic. In medicine, it's used to make people drowsy before surgery and as a way to produce memory loss so patients don't remember painful parts of the procedure. Midazolam is the drug set to expire in Arkansas, and its use has been controversial because of its role in recent botched executions in which patients remained conscious. Vecuronium bromide, which causes paralysis. In medicine, it's used in general anesthesia to relax the skeletal muscles during surgery.

which causes paralysis. In medicine, it's used in general anesthesia to relax the skeletal muscles during surgery. Potassium chloride, which is used to stop the heart. In medicine it's used to treat low blood potassium.

Over the past few years, drug companies have started blocking their drugs from being used in executions. These drugs also have other medical uses, which can make it tricky to keep them from making it into state prisons that still carry out the death penalty and to keep them from being used for that purpose.

In May, Pfizer, became the last pharmaceutical company to block the use of its drugs in lethal injections. Its decision meant there were no longer any Food and Drug Administration-approved manufacturers that would supply the drugs used in lethal injections for the death penalty.

"Pfizer strongly objects to the use of its products as lethal injections for capital punishment," the company said in its lethal-injection policy.

The move has made it harder for states to get the drugs for the purpose of lethal injection. Pfizer on Thursday said the drugs in Arkansas were sold to the state's Department of Correction without the company knowing:

"Pfizer did not directly supply the product to the Arkansas Department of Correction (DOC). Without Pfizer's knowledge, McKesson, a distributor, sold the product to the DOC. This was in direct violation of our policy. Pfizer has twice requested that Arkansas return any Hospira or Pfizer manufactured Restricted Product in their possession. In addition, we considered other means by which to secure the return of the product, up to and including legal action."

McKesson, the drug wholesaler that sold the vecuronium bromide to Arkansas DOC, refunded the money to the state and issued a restraining order against the DOC from using the drug in lethal injections. That restraining order was withdrawn after the executions were paused.

"We will continue our efforts to facilitate the return of our product and ensure that it is used in line with our supplier agreement," McKesson said in a statement.

Two other drug companies whose drugs may have been used in the executions, Freesenius (the suppliers of the potassium chloride) and West-Ward Pharmaceuticals (thought to be the suppliers of the midozolam), issued a brief as part of a lawsuit aimed at halting the lethal injections.