Berserkers

Berserkers (or Berserks) were Norse warriors who are reported in the Old Norse literature to have fought in a nearly uncontrollable, trance-like fury, a characteristic which later gave rise to the English word berserk.

Theories about what caused berserker behaviour include ingestion of materials with psychoactive properties, psychological processes, and medical conditions. Modern scholars believe certain examples of berserker rage to have been induced voluntarily by the consumption of drugs such as the hallucinogenic mushroom Amanita muscaria, commonly known as the fly agaric or fly Amanita, or massive quantities of alcohol.

From: http://en.wikipedia.org/wiki/Berserker

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