Det er sansyneligvis bare en myte. Siterer Wikipedia:
"That Nordic Vikings may have used fly-agaric to produce their berserker rages was first suggested by the Swedish professor Samual Ödman in 1784. Ödman based his theory on reports about the use of fly-agaric among Siberian shamans. The notion has become widespread since the 19th century, but no contemporary sources mention this use or anything similar in their description of berserkers. Today, it is generally considered an urban legend or at best speculation that cannot be proven."

Fly-agaric som det refereres til er rød fluesopp.