To prevent you from using medicine that’s less effective. Doctors want your to have a certain concentration in your blood to be within the therapeutic window. If the concentration is too low you won’t have the desired effect on you.
It’s mostly out of caution, just as the date is shorter than it could be to be extra safe.
Yes, some drugs break down into other compounds that can be toxic after their expiration date.
then why to the others have it?
To prevent you from using medicine that’s less effective. Doctors want your to have a certain concentration in your blood to be within the therapeutic window. If the concentration is too low you won’t have the desired effect on you.
It’s mostly out of caution, just as the date is shorter than it could be to be extra safe.