I take an allergy pill every morning. An antihistamine called Fexofenadine (an Allegra knockoff). And I have the hardest time remembering whether or not I took it. So, I often take another when I can't remember, because I'd rather overdose than get a day-long headache that prevents me from doing any work.
I'm not exactly sure what the consequences of OD'ing on antihistamines are, but I can't imagine two is going to kill me.
But, what if you're an old senile person on heart medication. How often do these guys kill themselves through prescribed medicine?