The Witcher 2 mutagens

In The Witcher 2, mutagens are powerful mutation-triggered agents. They allow you to raise your abilities even further. Mutagens can be acquired in two ways: you can loot them from defeated enemy corpses or you can create them using alchemy. To undergo mutation, enter meditation and then select the "Character" option and find an ability with a mutagen slot. Mutations cannot be reversed ; as such, it is strongly recommended that you never use lesser or basic mutagens, only greater ones. It is also recommended to have the impregnation talent from the alchemy tree at level 2 because mutagens aren't improved if you take the skill after having mutated an ability (to be verified).

Mutagens usually take one of three forms: lesser, basic and greater. Each of these forms raises Geralt's statistics by different amounts.