What is an antonym for concoction?

There isn't a single perfect antonym for "concoction" because the word has a bit of a nuanced meaning. It can refer to something:

* Mixed or prepared, often in a complicated way: In this sense, antonyms could be simple, natural, unmixed, or unprepared.

* Made up or invented: In this sense, antonyms could be genuine, real, authentic, or true.

* Something strange or suspicious: Here, antonyms could be ordinary, normal, expected, or straightforward.

The best antonym will depend on the context of how "concoction" is being used.