I'm sure there is some degree of companies wanting expiry to be like the dates on grocery items that are really "taste best by" dates but in speaking to manufac

I'm sure there is some degree of companies wanting expiry to be like the dates on grocery items that are really "taste best by" dates but in speaking to manufacturing and development people their are some layers of complexity. Compounds do degrade over time in many cases and things like light, temperature and humidity play a role. In pharmacy warehouses they aren't just required to control climate they have to log temperature 24 hours a day in an auditable format. Because of these factors the target is a moving one and while many things would likely be fine, for prescription medicine the tolerance for risk is so low that it pushes things in a very conservative direction. There is a great comment farther down about how complex label changes can be. Getting a revised label, or packaging through FDA is an enormous undertaking. This why sometimes dosing seems very weird. If research says we need a 2mg and a 4mg but later in the process patients need a .5mg it's a big mess. Suffice to say it's a deep rabbit hole.