well the first thing you need to check in a pain killer is "is your product solving the most crucial problem" like something which can not be ignored, can not be avoided or cannot be dealt with later, if those three things are covered,then your product upto some degree is a pain killer.

second you need to check weither the product you are offering is the best solution to address the problem in the most possible sense, and with a good ROI, or is the product just fixing one problem while leaving the rest, your are not expected to build a swiss army knife of sort but even then, a product which is not usefull in the sense of usability is just a vitamin.

to summarize in short, any product which is handling a crisis situation and providing a good ROI, without being much of a hassle is a pain killer.

~there are other aspect as well but i believe these two are the most important one's among all.