One of the things that determines whether a drug is available over the counter versus behind the counter or by prescription isn't just the potential for harm in case of overdose, but the potential for abuse and the potential for affecting public health. For example, if everyone could just grab amoxicillin whenever they want, we'd probably end up with a bunch of strains of medication resistant bacteria because a lot of people would take it every time they got symptoms that felt like being sick and wouldn't take enough for a long enough time to kill off all the bacteria exposed to the drug. Epinephrine has potential to be abused as a stimulant.