Berserkers in their characteristic animal furs and howling with frenzied rage. New research suggests that it was not red fly agaric, but the poisonous flower boletus that put the warriors in this deeply stunned and extremely aggressive state. Artist: Stefan Kopinski

The Secret Behind the Vikings’ Berserk Rampage Revealed

Icelandic sagas tell of fearsome Viking warriors who fought in a state of wild rage, immune to both pain and weapons.

Published: October 1, 2026, 9:25 am

    The myth of the toadstool has long dominated history, but new research instead points to a pale yellow flower as the source of the berserkers’ callous madness.

    The Berserkers are described in the old sagas as elite warriors who charged into battle in a ritualistic rage – the so-called berserk. Before the fight they howled like wild animals, bit their shields and threw off their armor. Once in battle they seemed completely unaffected by pain from both sword edges and fire.

    For centuries, it was believed that the rage was caused by red fly agaric, but historians and medical experts are now skeptical. Fly agaric makes people drowsy and disoriented. On a chaotic battlefield, it would have been a death sentence.

    New research by Canadian-Slovenian ethnobotanist Karsten Fatur instead shines the spotlight on the plant, which contains the potent alkaloids hyoscyamine and scopolamine, which affect the central nervous system in a way that is strikingly consistent with the behavior of berry maggots.

    Black henbane (Hyoscyamus niger) has characteristic pale yellow flowers with dark purple veins. This poisonous and delirious plant, which is now quite rare in Sweden and mainly occurs in the southern and central parts of the country, is pointed out in modern research as the biological explanation behind the once feared berserk. Photos: Petr Harant

    The toxic properties of the herb induce a so-called delirious state, with lifelike hallucinations and a loss of time perception. The user suffers from an acute delirium with violent fits of rage where all inhibitions are released. At the same time, the substances act as a powerful anesthetic. This explains the berserkers’ callousness; they could continue fighting despite fatal wounds because the poison blocked pain signals.

    The connection becomes particularly clear in the sagas’ own testimonies. They tell us that the berserk rampage began with chills and severe tremors, and that the warriors were afterwards struck by a paralyzing exhaustion that left them powerless for days – which are the exact physiological symptoms of a crash.

    The theory is supported by strong archaeological findings. In a Viking Age völva (a fortune teller) grave in Fyrkat, Denmark, a leather pouch filled with black henbane seeds was found. This proves that the Vikings knew about and used the plant’s mind-altering powers.

    Everything points to the berserk attack being a chemically induced psychosis. The black henbane gave the Vikings a biological weapon that dampened all pain and up the aggression to the max – and transformed ordinary warriors into the most ruthless elite soldiers of the time.

    Christer Ericsson

    christer.ericsson@nyatider.nu

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