Werewolf mutagen is an alchemy ingredient and is used to craft werewolf decoction. They act like lesser red mutagens when placed in the diamond-shaped slots in the character panel.

Like all special mutagens they can only be dropped by their corresponding creature. It is easy to obtain as it is guaranteed to drop from almost any werewolf (the few ulfhedinn have a high chance), multiple of which are encountered during main or otherwise significant quests such as The Whispering Hillock. Another early source of it, depending on choices, is the Wild at Heart quest.

Notes

• In an undocumented change for Patch 1.08, all mutagen icons were changed. However, there was still a bug for those on Steam and Origin that didn't reflect this and was later fixed in Patch 1.22. Despite this, some may still see the original icons instead, even with a fully patched game.
• It is possible to obtain a limitless amount of this mutagen by continuously killing Morkvarg during In Wolf's Clothing.
• A dead werewolf body with a mutagen can be found on a small island on Skellige.