As a fan of Random d20’s, I stumbled upon this interesting d20 regarding Strange Effects that can happen with Potions. Enjoy!
Unstable Potions – d20 strange and unexpected effects for your D&D potions
Magic is tricky business, and you cannot always trust your magic items to turn out, as you would expect. Small variations in ingredients and the intonation of magic words or perhaps exposure to magical auras and weird mysteries, and suddenly your potion of healing, growth, giant strength, flying or invisibility does work quite the way, you had hoped. Prepare yourself for unstable potions!
Here is a table of 20 effects, you can add to potions in your D&D game, in order to surprise and challenge your players. The rule descriptions are kept somewhat D&D agnostic and though based on the D&D 5th rules, they can easily be converted to your favorite version of D&D be it 3rd edition, AD&D or Labyrinth Lord. The table was originally designed for the Danish RPG The Hinterlands (Hinterlandet), and is here translated into English and adapted for D&D.