At the beginning of the story, my MC, a seventeen year old male, attempts suicide. He is bipolar, but up until the suicide attempt, he had been misdiagnosed as suffering from depression. My question is, what prescription drugs could he overdose on that could conceivably kill him? While he has been considering suicide for a long time, the attempt itself is spontaneous and, as such, he has no real plan as to how to do it. He's figured that overdosing was the way to go, but now he's alone at home, and desperate, and ready to pretty much try the first likely drug he can find.
I was considering Valium, or some other benzodiazepine such as a sleeping pill, as it would make sense for his mother to have a prescription (she suffers from anxiety) and therefore easy for a bottle to be lying around the house. However, I've read that benzodiazepines are only potentially fatal if taken with another depressant, such as alcohol, and I highly doubt my MC would know this. I need the attempt to be a valiant effort, one that more than likely could have killed him if not for intervention.
So, is a benzodiazepine overdose a possibility, and, if so, how much of it would constitute a potentially fatal overdose? Should the benzodiazepine be combined with another drug for maximum affect, and, bearing in mind that this is stuff he would have to find around the house, and that he doesn't really know the finer details of drug overdose, what drug could that be? A non-benzodiazepine sleeping pill? His anti-depressants? Or should I find another drug altogether, and if so, what are your suggestions?