That depends on the nature of the molecules, if they are unstable and easily oxidized or reduced, they may turn into another compound that may not be poisonous, of course, I won't want to try them out
Is there something called an expired poison? I don't think anyone would actually want to find out the answer to that.. Yes, they might be lethal if nothing else. It might also depend on the type of poison. More detailed and wiser explanation provided by wisdomtool
It kills before it expires and after....it kills again !(poison does not expire but it becomes more lethal maybe)
it is quite easy to find out, open it and take a sip, sit down and see what happened don't forget to post the result!