The notion that Vikings used A. muscaria to produce their berserker rages was first suggested by the Swedish professor Samuel Ödmann in 1784 . Ödmann based his theories on reports about the use of fly agaric among Siberian shamans . The notion have become widespread since the 19th century , but no contemporary sources mention this use or anything similar in their description of berserkers . Muscimol is generally a mild relaxant , but it can create a range of different reactions within a group of people . It is possible that it could make a person angry , or cause them to be " very jolly or sad , jump about , dance , sing or give way to great fright " .