Meth used to be available over the counter in pharmacies in the US.

No drug I'm aware of causes immediate death in normal usage, except perhaps those used for lethal injection. Would you like to elaborate on that? Tylenol, on the other hand, causes an unpreventable (no antidote) slow drawn out death over about a week, where your body will be slowly decaying and you have time to say goodbye to all your loved ones, if you take a few times the normal dose by mistake