system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does euthanasia require only a small pill, but executions require several large vials of chemicals?
gpt
The lethal injection method is actually controversial. There have been studies done that show the process may actually be quite painful if the doses aren't right. One of the drugs paralyzes the body, but sometimes you're still essentially awake for the rest of the process, and can feel everything that's happening. Some people don't care about this obviously because they think the person deserves to suffer. 

It would be a hell of a lot easier and probably less expensive to just overdose somebody on morphine. So to answer your question, there isn't some specific "euthanasia pill" for humans, but you could easily kill somebody with just one type of drug in a painless manner, whereas the lethal injection process is just unnecessarily complicated.