Lama Ole’s answer:
Everybody gets sick. Fifteen percent of humans have the chance to use pain relievers, and the rest suffer. One should definitely use the help one can get.
The process of dying, for example, is not influenced by painkillers. What happens while dying has nothing to do with chemistry. However, heavy use of painkillers does shorten life. We should simply think, “I am removing the pain”—then the karma is good. One shouldn’t think “I am shortening life,” because then the karma is bad. It’s easy—mind is boss.