Do you know if Eric had a history of an explosive temper before Littleton?
No, I don’t believe so. At least, not that we know of. His temper became a thing after his family moved the umpteenth time and to a place he hated out of all the places they’d moved to. Given Eric’s age range by the time they moved to Colorado, it’s likely a combination of unexpressed emotions/rage and hormones surging to a head. All his medication did was put a band-aid over it.