Probably no.
We currently have no concrete evidence to how the berserkers worked themselves up into such a frenzy, with mushrooms being just one of many theories. The myth that they used mushrooms comes from several places, one of its biggest factors being that other warriors from different cultures did use mushrooms (the Aztecs are one culture that did so I believe) before or during battle.
One of the good things about lemmy is I can change the title, and "what ruled" is a pretty cool title so POOF, now its the title!
edit: Ok nvm it wont let me change the title