system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is it so hard to kill people painlessly?

So the recent push in Arkansas to execute several death row inmates before their drugs expired has me wondering. Why do we need such specially produced drugs to execute people?

It seems trivial that the human body is fragile enough that stopping it from working is a minor issue itself. People die without even trying all the time. In fact, we have to work hard to keep that from happening. So the problem is apparently doing that painlessly. But people can also be numbed, aneththetisezed, "put under" in a million ways, and if you disregard future health effects, a million more.

I guess I'm just in doubt that with all the drugs and their various properties that exist for so many reasons, it's only this specially produced combination that can reliably do the jobs involved. Why can't we use the many other drugs which at large dosages will numb past pain and end a life?
gpt
It isn't hard at all to kill a person painlessly. A bullet through the brain stem will do the trick almost every time. Decapitation is also painless. The issue here is that it is seen as barbaric and cruel not only to the prisoner, but to the persons pulling the trigger on the device that kills them.

There are many different kinds of ways to kill a person painlessly, and here in the USA we use a variety of different methods depending on which state you're in. Some states use a single drug (usually a lethal dose of an anesthetic like pentobarbital or a paralytic agent like pancuronium bromide), some states use a three drug system starting with a dose of midazolam (a sleep agent), then hydromorphone (a painkiller), then a lethal dose of potassium chloride.

There are two issues with these methods; the first is that the drugs are expensive and are prone to shortage (not enough companies are allowed to make them), and the second is that *they don't always work as intended*. There have been several botched executions using these kinds of drugs on prisoners.

Recently, many states are switching to a new method which is inducing nitrogen hypoxia (like you get during dental and medical procedures, just with a more prolonged dose) with nitrous oxide. Tennesee still allows the electric chair, Utah still allows a firing squad, and New Hampshire still allows hanging. 

tl;dr Killing people painlessly isn't a problem, it's just that we use drugs to do it, and drugs don't work the same on every living person.