A recent question https://pets.stackexchange.com/questions/20998/cat-suddenly-became-paralyzed?noredirect=1#comment28553_20998 has a cat with sudden onset paralysis, after starting a new drug.  The companies drug literature does not list this as a side effect, but the OP found that several pet owners had seen paralysis after administering the drug. 

> although I did find pet-owners who had the same experience on related forums.

User comments suggest that as the side effect is not listed by the manufacture it could not possibly be related [1](https://pets.stackexchange.com/questions/20998/cat-suddenly-became-paralyzed#comment28551_20998) & [2](https://pets.stackexchange.com/questions/20998/cat-suddenly-became-paralyzed#comment28553_20998) 

> You've done the research and there really isn't any reason to think there's a link between the felimazole and your cat's new symptoms. 
>
> I'm referring to the listed side-effects from studies.

What are the actual legal requirements for pet medications?  Does the vet or the manufacture need to report this possible side effect?