I believe it’s already been mentioned, several of the execution drugs do have a therapeutic purpose.
Sodium thiopental is a barbiturate used pretty regularly therapeutically. In fact it is, per wiki:
Pancuronium bromide is a muscle relaxant frequently used in surgery.
Potassium chloride is just a salt, and not controlled or limited by manufacture at all. It’s easily obtainable by you or me and is even a table-salt substitute. A huge dose of it stops the heart, but it can’t be used by itself because I believe the effect would basically be akin to giving someone (and making them endure) a heart attack and that’s unlikely to pass the “cruel and unusual” sniff test.
The logic of the three drug cocktail starts with potassium chloride being pretty effective at stopping the heart, so that insures with a high likelihood the person is going to die. Pancuronium bromide when given in execution doses basically shuts down all your muscles including your diaphragm and thus would cause you to asphyxiate (so yet another lethal dose of a drug being administered.) The sodium thiopental is a powerful anesthestic, so the negative/unpleasant experience of being dosed with the other two injections is not experienced by the condemned as sodium thiopental (or pentobarbital) is administered first.
Both pancuronium bromide and potassium chloride would be unpleasant to experience conscious. The pancuronium bromide you’d basically die of suffocation, potassium chloride apparently when injected at a high dose is extremely painful at the IV point and then all the way up the through the vein as it travels, and then eventually it will cause your heart to stop.
So all the materials used in a lethal injection do have therapeutic use. I don’t know if a regular CVS would carry either sodium thiopental or pancuronium bromide as they appear to primarily be used in a surgical setting (I’m guessing they’d be regularly available at a hospital, though.)
One of the longstanding concerns with the three drug cocktail is two of the three drugs would cause a lot of suffering if the person wasn’t properly anesthetized by the first drug. This is why some States have moved towards a one-drug approach using only sodium thiopental or pentobarbital as it basically is “failure proof.” The condemned is just given a massive does of the barbiturate, they lose consciousness and die. No worrying about the other two drugs working.
But it’s also the first drug in the cocktail, the barbiturate, that has been supply limited. A Danish company is the only manufacturer of pentobarbital and an American company with a factory in Italy was the only supplier of sodium thiopental and both sources have taken measures to prevent their product being used in lethal injections. So the States that went to the one drug method don’t have any option for those drugs other than a compounding pharmacy.
They’ve also considered using propofol (of Michael Jackson fame) to replace the barbiturates, but apparently the company in Europe that manufactures it threatened supply restrictions if it was used in an execution so Missouri abandoned its plans to use the drug. [As a side note I find it strange with all the U.S. pharmaceutical companies we don’t appear to have any domestic production of three different anesthetic agents that at least appear to be used somewhat frequently in clinical settings.] I would guess propofol probably is stocked in a regular pharmacy? If Michael Jackson’s GP was able to get it regularly for him, anyway.
In places like the Netherlands that have physician assisted suicide a high barbiturate dose to start followed by using pancuronium bromide to stop breathing is considered part of the standard protocol.