So if I tell you I want you to poison me to death with a bottle of poison marked with a skull and crossbones which contains poison and has a label on it saying 'poison', and you do so, it isn't poison? But if you feed me cake without my consent it is a poison? Nicotine, consensually smoked in a cigarette, is not a poison?
Are you sure?
I just looked it up and it said "A poison is any substance that causes harm, injury, or death to a living organism when absorbed, ingested, or inhaled in sufficient quantities." Nothing to do with consent.
That said... who cares? The 'medical definition' (if one can agree on what that is, and I image every medical authority on the planet has its own definition) is hardly the point here, is it? It's a giant sidetrack on a thread about mind control, which I'm sure there isn't a medical definition of, being fictional and all.