I'll chime in. Most chemical processes happen faster with a higher temperature. Some drugs decay into harmful substances (e.g. Aspirin). Other factors, such a

I'll chime in. Most chemical processes happen faster with a higher temperature. Some drugs decay into harmful substances (e.g. Aspirin). Other factors, such as humidity or UV, may play a part as well. Rather than testing every permutation of storage conditions over time, manufacturers put a safety margin. Individual consumers aren't in a position to remember exactly how they treated any given container of pills. Even if the manufacturer knew how a given sequence of storage practices affected their drug, nobody would be the wiser.