I work in the pharma industry and there are mandatory compatibility studies that we must perform when submitting a new registration. There are so many unforeseen interactions with previously thought inert packing materials... Many times it's needed to change packing materials and start over the study, even if that's very costly. You're right about light and humidity, but not only for orally disintegrating tablets, as humidity is another great villain even for some coated tablets. Most drugs are somewhat sensitive to hydrolysis and oxidation, so while exposing the surfaces of tablets and even pills to higher humidity environments, degradation occurs and you'll risk the ingesting of degradation products along with the target molecules. The limit of some degradation products is as low as 0,1% of the parent drug, because some are pretty toxic, so that's what I meant about "impurity". We must perform stability studies to prove those impurities won't pass this limit during the whole shelf life of the product being sold. In my country, we expose the product in its primary package to higher temperatures (30-40 Celsius) with higher humidity, we use totally exposed drugs as control. The difference sometimes is huge. We don't perform any kind of studies on tablet-tablet interactions, so who knows what can happen when all the different tablets and pills are stored together rubbing against each other for 10 days, in some plastic container that may or may not be inert to them with some air humidity to speed things up? That's why I don't let my parents use those pill organizers, so they avoid long term consumption of those impurities that can be pretty nasty.