My alchemy system tried at first to imitate the Dragon's Breath's one which is awesome: you pick ingredients, you mix them in different ways (grinded, cut, mixed, cooled, hot...) and deliver the spell. 

My  original idea was to replicate this making a list of ingredients with their potential effects and uses, side effects, etc. Here is a preliminary ingredient chart (in Span

Quite soon become obvious that this was a lost battle: managing nearly a dozen of different ingredients (the names being anagrams of original ingredients from Dragon's Braleath) means that you have to buy them separately, track them and, from a design point of view, balance them at least a bit (it's great that some mixture is very powerful on purpose and even funnier if players can design their own but the risks of unexpected game-breakers is high) and even then, the learning curve can ve very step. I fixed this somehow first allowing all ingredients work for everything, just some were better in certain areas than others. Still, the number of different side effects and combinations were just overwhelming. I then simplified the ingredient list to just five but even the potential for combinations was still too high. 

Eventually, I removed the concept of different ingredients and made them generic which works better. 

I might still recycle the concept for another game, though.