De Vries' extract

"The talented sorceress Tissaia de Vries is credited with discovering this powerful potion, which won her considerable renown. The potion improves the imbiber's vision and allows opponents to be detected even through walls."

De Vries' Extract potion makes concealed creatures visible.

Preparation	Base	Duration	Toxicity
De Vries' Extract is made by mixing: one Rebis, one Aether, one Hydragenum, and two Quebrith	top quality base	1 hour	Medium

Source

• Formula for De Vries' Extract
• Receiving this potion from the druids in Act V, during "The Green March" will unlock the formula if you did not have it already.

Trivia

• In Berengar's notes on the Beast, it's suggested that with the help of a potion (probably De Vries' Extract), one might be able to see the Beast. This, however, isn't really true. The potion does allow Geralt to "see" the beast seconds sooner than he would otherwise in the "non-final" encounters he has randomly with the hound at night. Also, the beast does initially have a blue circle under him, so it seems like dialogue would be possible, but then it disappears as always. In the final encounter, the beast appears before the cut scene even ends, so the potion would be useless.
• Geralt can find De Vries' Extract as an unknown potion on one of the Mangled Corpses near the Clay Pits in Act II.